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Ultrasonic metal welding machines are suitable for various complex applications (e.g., battery tabs) through unique mechanical design, special pressure application methods and high-precision welding. This work reports the weldability, forming quality and fractographic analysis of copper multilayered welded joints which were studied by SEM-EDS characterization, micro-hardness testing and tensile testing based on ultrasonic double roller welding (UDRW). Three groups of process parameters (A, B and C) were established to investigate the performance, production quality and welded joint surface interconnections. The tensile testing results of sample under parameter 3 in group A [S-P3(A)] indicate the maximum tensile strength of 69.859 N in T-peel test while the average tensile strength has increased by 58.525 N due to rise in welding time from 2 sec to 5 sec. The results analysis indicates that welding quality features in S-P3(A) joints under 4 bar, 100 mm/s, 45 % have been exploited. The over-welded zone was transformed into good-welded zone. The micro-cracks, fatigue stations and peeling texture in multilayers were reduced. It was found that when the welding energy was 10000 J then the tearing edges and interlayers cracks were minimized while keeping the other parameters constant. Moreover, when the amplitude increased up to 50 %, then numerous micro-cracks and micro-fissure stations were created, which leads to the occurrence of fracture in multi-layer welded joint. The EDS study investigated that the complex features are formed at the interface junction of sample 3 S3(A) in multilayer welds. The complex multilayer microstructures can induce and produce unique hardness properties for battery manufacturing. It leads to high quality and durable welds. Eventually, it is experimentally demonstrated that robust 40 layer welded joints can be obtained by the UDRW process. The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request. • Low amplitude used to minimize the damage of a workpiece, reduce metal debris and heat. • The study reports 40 layers of 0.2mm Cu thin foils welded joints using ultrasonic seam welding technology. • Tensile testing of S-P3(A) indicate maximum strength with 69.859N due to incremental upturn in time from 2sec to 5sec. • Welding quality features in S-P3(A) joints under 4bar, 100mm/s, 45%: (a) inside cross-sectional view were investigated. • Weldability, forming quality and fractographic analysis of Cu welded joints were studied by SEM-EDS characterization. [ABSTRACT FROM AUTHOR]

The effect of plastic deformation on the hydrogen embrittlement behavior of high-strength martensitic steels was investigated using a U-bend test. The hydrogen embrittlement susceptibility appeared to be enhanced with increasing plastic strain. Based on fractographic and stress-strain analyses, the maximum principal stress dominated the hydrogen embrittlement fracture. Although an apparent enhancement with increasing plastic deformation was observed, the origin of this enhancement was increased residual stress arising from the evolution of graded plastic strain during U-bending. We conclude that residual stress, rather than plastic strain induced by plastic deformation strongly affects hydrogen embrittlement susceptibility in deformed high-strength steel components. • Hydrogen embrittlement susceptibility of U-bend specimens was independent of plastic strain. • Maximum principal stress was the primary criterion for the hydrogen embrittlement susceptibility. • The apparent decrease in hydrogen embrittlement resistance with reduced bending radii was due to increased residual stress. [ABSTRACT FROM AUTHOR]

To assess the influence of calcination process on the properties of minimally processed recycled 3Y-TZP, and to compare it with its commercial counterpart. Non-milled 3Y-TZP waste was collected, fragmented and ball-milled to a granulometric < 5 µm. Half of the recycled powder was calcined at 900 °C. Recycled 3Y-TZP disks were uniaxially pressed and sintered to create two recycled groups: 1) Calcined and 2) Non-calcined to be compared with a commercial CAD/CAM milled 3Y-TZP. The microstructure of experimental groups was assessed through density (n = 6), scanning electron microscopy (n = 3) and energy-dispersive X-ray spectroscopy (n = 3); and the crystalline content was evaluated through X-ray diffraction (XRD) (n = 3). Optical and mechanical properties were investigated through reflectance tests (n = 10), and Vickers hardness, fracture toughness (n = 5), and biaxial flexural strength tests (n = 16), respectively. Fractographic analysis was performed to identify fracture origin and crack propagation. Statistical analyses were performed through ANOVA followed by Tukey´s test, and by Weibull statistics. Particle size distribution of recycled powder revealed an average diameter of ∼1.60 µm. The relative density of all experimental groups was > 98.15 % and XRD analysis exhibited a predominance of tetragonal-phase in both recycled groups, which were similar to the crystallographic pattern of the control group. Cross-section micrographs presented flaws on the non-calcined group, and a more homogeneous microstructure for the calcined and commercial groups. Commercial samples showed lower contrast-ratio and higher translucency-parameter than the recycled groups, where non-calcined presented higher translucency-parameter and lower contrast-ratio than its calcined counterpart. The commercial group presented higher fracture toughness and characteristic strength than the recycled groups. Moreover, the calcined group exhibited higher hardness, characteristic strength, and probability of survival at higher loads than the non-calcined group. Fractographic analysis depicted the presence of microstructural flaws in the non-calcined group, which may have acted as stress-raisers and led to failures at lower flexural strengths values. The calcination process improved the microstructure, optical, and mechanical properties of the recycled 3Y-TZP. • Effect of calcination on minimally processed recycled zirconia powder was assessed. • Calcination enhanced the microstructure, optical, and mechanical features of the recycled 3Y-TZP. • Calcination did not promote alterations to the crystalline structure of the recycled 3Y-TZP. • Calcined powder resulted in a more homogeneous microstructure. • Recycled 3Y-TZP demonstrated a potential for applications in reconstructive dentistry. [ABSTRACT FROM AUTHOR]

Tribological characteristics of fine-grained dual-phase high-entropy carbide/boride ceramics were investigated using the ball-on-flat dry sliding method in air, applying linear reciprocation motion with SiC counterpart. Detailed fractographical analyses were used for the characterization of the deformation and damage mechanisms. The investigated system with composition (Ti 0.14 Zr 0.2 Nb 0.2 Hf 0.2 Ta 0.26)C + (Ti 0.38 Zr 0.18 Nb 0.22 Hf 0.115 Ta 0.105)B 2 showed density with value 8.72 g/cm3 and very high hardness of HV1 29.4 ± 2.0 GPa. The friction coefficient at the test with 5 N was 0.56 and during the test with 10 N and 25 N loads were 0.48 and 0.5, respectively. The effective wear rates at the loads of 5 N and 25 N were very similar with values of 7.93 × 10−7 mm3/Nm and 6.63 × 10−7 mm3/Nm. At load 50 N the effective wear rate is significantly higher with a value of 9.11 × 10−6 mm3/Nm. Detailed fractography revealed that the dominant wear mechanisms at loads of 5 N and 25 N were an oxidation-driven tribochemical reaction and tribo-layer formation in boride grains and mechanical wear in carbide grains and at the load of 50 N fracture of boride and carbide grains and formation of chemically complex tribolayers. [ABSTRACT FROM AUTHOR]

The fracture behaviour of grains and grain boundaries plays an important role in the design of novel ceramics with improved macromechanical deformability. This was investigated first time in a dual-phase high-entropy carbide/boride ceramic, using microcantilever bending, linear beam theory and micro/nanofractography. Microcantilevers were focused ion beam milled from the carefully polished sample surface with random locations containing both carbide and boride grains and grain boundaries in the beam volume. Scanning electron microscopy-based fractography analysis revealed that the bending strength of grain/phase boundaries varies in the range of 0.9–6.7 GPa, depending on the orientation and location of the boundaries in the beam. The fracture of carbide grains was found to be initiated mainly on submicron size volume defects with strength values of 4.5–9.5 GPa, while the fracture origin in most boride grains was identified as surface defects introduced by specimen preparation, which resulted in higher fracture strengths of 9.0–12.3 GPa. [ABSTRACT FROM AUTHOR]

This study aimed to perform a thorough failure analysis of two fractured narrow dental implants after medium-term in vivo use. The top parts of two fractured Narrow Dental Implant (NDI) fixtures were retrieved from two different locations at two different times from the same patient. The NDI-specimen-1 was 12-months in service while the NDI-specimen-2 was 17-months in service. In both cases, the top parts of the fractured NDI fixtures that were attached to prosthetic components were retrieved and subjected to thorough, non-destructive and destructive testing. Light Microscopy (LM) and Scanning Electron Microscopy (SEM) revealed that both the retrieved fractured NDIs failed because of fatigue, characterized by beach and ratchet marks. Macroscopic examination revealed that fatigue cracks initiated at the internal thread surfaces of the implants and propagated around them until final fracture. Both samples fractured near the end of the retaining screw and followed the root of the internal thread. Optical and SEM analyses revealed a uniform distribution of irregularly shaped grains (diameter = 2 to 5 μm). X -ray Energy Dispersive Spectroscopy (EDS) analysis showed that the NDI-specimen-1 was made using Ti-14%Zr with a Vickers Hardens (HV) of 288 ± 5. Since the fracture occurred by a fatigue; thus, an increase in fatigue resistance will be beneficial for the longevity of NDI. [ABSTRACT FROM AUTHOR]

This study aimed to compare the four-point flexural strength of CAM-milled and sintered (as-sintered, AS) specimens with those of high-polished (HP) specimens using chairside polishing systems to simulate clinical surface conditions. Seven full-contour zirconia CAM/CAM blanks with various yttria contents (3, 4, 5 mol%) including three high-translucent groups (5Y) were selected to prepare flexural specimens. The bend bar specimens (2.0 × 4.0 × 25.0 mm3) were fabricated by using STL file and dental CAM machine with the respective zirconia blanks (98 mm ϕ and 10–14 mm in height). Twelve bar specimens were machined from one zirconia puck and a total of 24 specimens were prepared from each group. The pre-sintered bar specimens were sintered by using a dental zirconia furnace at 1530–1550 °C for 2 h according to the instructions. All sintered specimens were divided into two groups: as-sintered (AS) group and high-polished (HP) groups (n = 12). HP groups were subjected to polishing one surface of specimens using a three-step polishing system and finally finished with diamond polishing. After cleaning and drying, the flexural strength of all specimens was determined by a fully articulating four-point flexure fixture consisting of a 1/4-point test configuration with an inner/outer span of 10/20 mm. Statistical differences between AS and HP groups were conducted with Weibull analysis. The fractured surfaces of zirconia specimens were observed using a field emission SEM and EDS to detect failure origins. The mean AS flexural strength values were significantly lower than those of HP counterparts. However, Weibull moduli expressing the reliability of HP groups were generally decreased although not significantly in comparison to their AS. The fracture of the AS specimens mostly originated from extrinsic CAM-milling defects, while the HP specimens were fractured from intrinsic subsurface or volume defects including pores, large grain clusters, inclusions, and corner-located critical flaws. Two high-translucent (5Y) zirconia groups were not affected in their strength and reliability after polishing, whereas one 5Y zirconia significantly increased its strength but significantly lowered its reliability. The extrinsic and intrinsic strength-limiting defects should be considered in evaluating the flexural strength and reliability of dental CAD/CAM zirconia ceramics for full-contour restorations. For the materials tested in this study, more optimized processing of blanks and milling protocols of pre-sintered zirconia blanks should be developed including post-sintering surface finishing to reduce the flaw population regulating strength and reliability which will affect the survivability of dental zirconia prostheses. [Display omitted] [ABSTRACT FROM AUTHOR]

The present investigation used atmospheric plasma spray (APS) as a method for the production of thermal barrier coatings composed of Yttria-stabilized zirconia (YSZ). A CO 2 laser was used to remove surface cracks from the YSZ coatings' surface. Several parameter variations were applied to generate laser-glazed tracks on the coating surface, resulting in an impure surface microstructure with excellent surface properties. Scanning electron microscopy was utilized to analyse the tracks' microstructure. The optimal laser parameters were determined to be 77.7 W laser power, 215 mm laser distance, and, 120 mm s−1 scanning speed based on microstructural characteristics. Once the laser parameters had been optimized, a whole coating surface was laser glazed. In order to ascertain the impact of laser glazing, stability analysis, fracture toughness, and hardness evaluations were conducted on both unglazed and laser-glazed coatings. The growth of a network of cracks was seen on the surface. The surface roughness exhibited a reduction of about tenfold in comparison to the unglazed YSZ. The presence of the monoclinic ZrO 2 phase within the coating structure was successfully eradicated. The laser glazing process resulted in enhancements to both the fracture toughness and surface hardness of the coating. Despite the fact that the gaps and imperfections on the coating surfaces were repaired during laser glazing, some cracked structures nonetheless appeared. Nano YSZ was deposited on laser-glazed surfaces by the electrophoretic method in order to eliminate cracks from laser-glazed surfaces. The experimental results obtained from conducting calcium-magnesium-alumina-silicate (CMAS) and hot corrosion tests on laser-glazed coatings indicate that the use of nano YSZ filler leads to a significant reduction in salt penetration during both glassy melt and hot corrosion processes. [ABSTRACT FROM AUTHOR]

The state-of-the-art fractographic guidelines for glasses and fine ceramics, ASTM C1678, are only applicable to limited fracture scenarios. This work outlines a new method to analyze fracture scenarios outside ASTM C1678′s scope. The proposed methodology consists of a two-step process: initially, optical images of the fracture surfaces are obtained, and visual analysis is used to highlight the characteristic fractographic features. Next, the selected features are automatically compared to a baseline set of virtual fracture patterns tailored to any relevant fracture scenarios obtained by numerical phase-field simulations. As validation, scenarios with fractures originating at the glass plates' edges for both sharp and chamfered corners were analyzed. Strength estimates within 6% of experimental results were achieved with the proposed method. In the future, this technique could be implemented to carry out fractographic analysis on brittle components of arbitrary shapes and loadings, hence substantially extending the application range and accuracy of fractographic methods. [ABSTRACT FROM AUTHOR]

The aim of the study was to develop new adhesive formulations that include natural polyphenols extracted from green tea (GTE), tricalcium phosphate (TCP) and chitosan to improve dentin bonding characteristics and cytotoxicity. Four experimental adhesives were formulated under laboratory conditions. The groups differed in the integration of either GTE and/or TCP + chitosan. The four experimental and one clinically proven reference adhesive underwent shear bond testing after 24 h and 6 months of aging (n = 200) with subsequent fractographic analysis. Bond morphology was analyzed under a scanning electron microscope. The presence of phenolic compounds was validated by high performance liquid chromatography. Cytotoxicity was assessed by the WST-1 colorimetric assay on eluates up to 6 months. Statistical analysis was performed by one- and three-way ANOVA, Games-Howell and Tukey's post-hoc test as well as multiple students t-tests (α = 0.05). Weibull analysis was further conducted. The addition of GTE into the bonding agent did show immediate (p = 0.023, p = 0.013) and long-term (p < 0.001) effects on bond strength. After 24 h, GTE doped groups performed equal to the reference (p = 0.501, p = 0.270) and TCP and chitosan displayed improvements in reliability (m=4.0, m=4.3). Bond strength is retained after aging by adding GTE (p = 0.983). The additional presence of TCP and chitosan reduces it (p = 0.026). Excluding cohesive and mixed failures, the reference adhesive performed statistically equal to three of the four experimental groups. No long-term cytotoxic effects were shown. The integration of GTE can enhance bond strength and a calcium source helps to improve immediate bond reliability. • Synthesis of adhesives containing polyphenols, tricalcium phosphate and chitosan. • Similar bond strength values compared to a gold standard control. • Improvement of bond strength by natural polyphenols. • Improvements of bond reliability by tricalcium phosphate and chitosan. [ABSTRACT FROM AUTHOR]

Mechanical and thermal processing of wire-arc additively deposited stainless steel is investigated with the purpose of improving its microstructure, surface morphology, formability, and stress response. Microscopy helps identifying the processing conditions that permit full recrystallization of the as-built columnar microstructure. Combination with strain loading paths, topography and fractography in tensile tests show that mechanical processing consisting of 20 % thickness reduction followed by annealing at 1100 °C under 4 h eliminates anisotropy and increases the fracture forming limits by 30 %. The work is a step forward to consolidate the hybridization of wire-arc additive manufacturing with metal forming as an alternative to conventional manufacturing. [ABSTRACT FROM AUTHOR]

Equibiaxial flexure strength of two commercially available zinc sulfide (ZnS) materials along with an in-house manufactured calcium lanthanum sulfide (CLS) material was determined and compared to strength values reported in the literature. The strength of the multispectral (MS) ZnS and the in-house CLS were the same while the chemical vapor deposited (CVD) ZnS had a strength almost twice as high. Fractography was conducted and the crack branching constant (A b) was determined for each material, as well as the feature that limited the strength. In the case of the CVD ZnS large ZnS grains coupled with damage from the polishing procedure limited the strength while only large ZnS grains appeared to limit the strength of the MS ZnS. Fractography of the CLS material was challenging. Large grains were identified as the fracture origin in half of these specimens, but the origin could not be unequivocally identified in the remaining specimens. [ABSTRACT FROM AUTHOR]

The fracture mechanism of hydrogen charged Ti–6Al–4V has been investigated through a multianalytical approach. The difference in hydrogen solubility between β phase (high solubility) and α phase (low) governs the formation and growth pattern of titanium hydrides, and determine the fracture mode of Ti–6Al–4V. Depending on the hydrogen charging extent, the penetration of hydrogen and distribution of hydrides can be divided into three stages. In the initial stage hydrogen diffuses mainly into the β phase, as judged from its increase in Volta potential, and with no hydrides formed. Failure analysis after tensile tests exhibits plastic behavior and a fracture surface with mainly dimples. In the subsequent transition stage, hydrides are formed at the α/β interfaces and along α grain boundaries. More initial cracks occur in the brittle hydrides and the fracture surface transforms from dimple to quasi-cleavage. In the final stage a layer of uniformly distributed hydride is produced on the surface and within the α phase. Supported by nanoindentation measurements, the plasticity of the charged sample diminishes with hydrogen charging time, and an intergranular-transgranular mixed fracture is observed. Overall, the study forms clear evidence that the distribution and cracks of hydrides influence the fracture mode of the Ti-6A-4V alloy. • Hydrides form at α/β interface, grow along α grain boundaries, and occupy α grains. • Cracks initiate and propagate through soft-brittle hydrides. • The presence and distribution of hydrides determine the mode of fractures. • Hydrogen permeation increases the Volta potential difference between β and α phases. [ABSTRACT FROM AUTHOR]

Melt-grown Al 2 O 3 –ZrO 2 eutectic ceramics have attracted extensive attention for harsh environment applications. In this work, Al 2 O 3 –ZrO 2 eutectic ceramic is additively manufactured via one-step laser powder bed fusion (LPBF). The effect of laser focus shift on the relative density, phase formation, microstructure evolution, and mechanical properties was systematically investigated. The as-fabricated specimens are dominated by α-Al 2 O 3 and t-ZrO 2. The m-ZrO 2 phase increases with increasing the laser defocus shift. The cellular-like structure formed when convection dominated at focal plane, while colony eutectic structure occurred when eutectic growth dominated at higher defocus shift. The deformation of cellular-like structure and needle-like ZrO 2 into concave cells and dendritic structures is principally determined by the evolution of solid/liquid (S/L) interfaces. With the formation of needle-like or dendritic ZrO 2 ductile phase, the crack propagation is prevented, leading to progressively enhanced fracture toughness with a maximum value of 8.04 MPa m1/2. [ABSTRACT FROM AUTHOR]

To investigate the influence of the presence and position of bidirectional E-glass fibers under a CAD-CAM resin composite on the fracture pattern evaluated both after quasi-static mechanical loading and after fatigue. Rectangular specimens (10 mm-long, 5 mm-large and 4.2 mm-thick) were prepared and divided into four groups (n = 30/group). The control group (C-Group) consisted of a 4.2 mm-thick layer of monolithic CAD/CAM resin composite resin (Cerasmart, GC). In the 3 other groups including the placement of a fiber layer (F-Groups), the CAD/CAM resin composite layer was reduced to 3-, 2- and 1-mm thickness (F3-, F2- and F1-Groups, respectively). Two bonded layers of bidirectional E-glass FRC (Dentapreg, ADM A.S.) were bonded underneath and a light-curable resin composite base (Gaenial Posterior, GC) was then added to reach a total thickness of 4.2 mm for all samples. In each group, half of the specimens (n = 15) were submitted to quasi-static mechanical loading to failure in a universal testing machine. The other half (n = 15) was subjected to cyclic isometric stepwise loading until failure or completion of 105000 cycles (5000 cycles at 500 N, followed by five stages of 20000 cycles at 750 N, 1000 N, 1250 N, 1500 N, and 1750 N). The data were analyzed by Weibull statistics for quasi-static loading, and by the Kaplan-Meier product limit estimation procedure after fatigue. All fractured specimens were studied using light and electron microscopy techniques, and the types of fracture were determined. For quasi-static mechanical loading, significant differences were observed for Weibull modulus and characteristic strength between groups, with values ranging from 10.8 to 22.4 for the former and from 2336.6 to 2974.7 for the latter. Also, survival after stepwise fatigue revealed statistically significant differences between groups (p < 0.05), the lowest values of cycles before failure being observed for F1-Group – Median = 61223 (50415; 65446) – as compared to the other groups – C-Group: Median = 89005 (86189; 98195); F3-Group: Median = 85198 (77279; 87860); F2-Group: Median = 89306 (87454; 97024). Both in quasi-static loading and after fatigue, the observation of fracture modes revealed major differences. While all fractures were vertical (split) in C-Group, the majority of the specimens in F-Groups presented some degree of horizontal deflection of the crack. In all deviated fractures, fractographic analysis confirmed a toughening effect of the fiber layer. The present in vitro work tends to show that the fracture pattern of CAD-CAM resin composites is favorably affected by the presence and position of an underlying bidirectional E-glass fiber layer. The placement of E-glass fibers under a CAD-CAM resin composite may therefore represent an interesting strategy to reduce the risk of catastrophic restoration failure, which could be integrated in the development of the new generation of indirect materials, possibly in 3D-printing approaches. [ABSTRACT FROM AUTHOR]

The present paper aims to propose a reliable analysis of ball-on-three-balls and four-point bending experiments applied to advanced ceramics combining statistical analyses, numerical modelling and fractography. MgAl 2 O 4 transparent spinel ceramic was selected to facilitate the assessment of samples quality. Following the material processing procedure detailed in the literature, numerous spinel samples of two different geometries (20 and 60 mm in diameter) were produced. Knoop Hardness and Young's modulus values of 11.8 GPa and 290 GPa were measured, respectively. A three-modal grain size distribution was observed through the sample's thickness. Biaxial bending tests have been performed in conjunction with numerical simulations using Abaqus/Standard®. Thus, parallelism defects were taken into account and their effects on the maximal stress and effective volume were quantified. They were found to be very close to the only published data. In addition, four-point bending experiments were carried out and validated using an ultra-high-speed camera. The scattering of the bending strength was modelled using a two-parameter Weibull distribution and the maximum likelihood approach. 90% confidence intervals of the parameters and confidence bounds of the probability of failure were computed using the likelihood ratio test. This approach is more suitable than Monte Carlo simulations with regard to computational costs. According to the Weibull theory and biaxial bending strength distribution, the material strength, rescaled for different effective volumes was slightly overestimated, in comparison with four-point bending results. Fractographic analyses on uniaxial bending samples revealed that fractures originate from large grains. The corresponding study on biaxial bending samples revealed that carbon inclusions located near to the surface seem to be responsible for failure. Finally, this study brings additional arguments for a more intensive use of the ball-on-three-balls set-up especially when concerns about costs, sample geometry and test practicality are raised. [ABSTRACT FROM AUTHOR]

The cold sintering process (CSP) densifies ceramics below 300 °C by utilizing a transient phase and applied pressure. Although CSP has been employed for densifying a variety of functional systems, their structural integrity does not always reach that of conventionally sintered parts. On the example of ZnO, this study aims to eliminate processing-induced defects that compromise the strength of cold sintered materials. Ultrasonic evaluation was employed for nondestructive detection of flaws prior to mechanical testing. Load transfer misalignments and fast heating rates were found as major sources of defects, impairing the mechanical strength. Based on these findings, multiple disc-shaped samples (13 mm diameter and ∼1.3 mm thickness) were cold sintered simultaneously using precisely aligned punches and slow heating rates. The obtained homogeneous densification, high relative density (>97%) and relatively high strength (∼120 MPa), i.e. two times superior to previously reported values, demonstrates the feasibility of scaling up the CSP towards industrial implementation. [ABSTRACT FROM AUTHOR]

The strain-controlled cyclic deformation behaviour of Mg-9Gd-4Y-2Zn-0.5Zr with different structures was investigated. Alloys were prepared by solution, extrusion and pre-ageing extrusion, and the microstructures before and after the fatigue tests were characterized. Experimental results indicated that the bimodal structure owned the better performance in fatigue test, which was attributed to the higher yield strength. For the equiaxed structure, cyclic hardening induced stress concentration until the failure. Stable cyclic deformation and persistent cyclic softening played an important role at the low and high strain amplitudes, respectively. This was attributed to the formation of fine grains relieving the stress concentration during cyclic loading. In addition, residual twins were observed in equiaxed structure to induce crack, and the bimodal structure effectively restrain it. [ABSTRACT FROM AUTHOR]

• Finer β -Mg 17 Al 12 increased corrosion during the first immersion hours. • The ultrasound-treated samples are characterized by uniform corrosion. • Non-treated samples showed severe localized corrosion regions. • Material degradation negatively impacts the mechanical properties of non-treated samples. • Ultrasound treatment can be used to produce Mg-based stents with controlled degradation. Magnesium-based materials show great potential for producing biodegradable stents, but their high corrosion rates are a roadblock. This study investigates whether ultrasound melt treatment can change the corrosion response of an extruded AZ91D-1.0%Ca (wt.%) in Earle's Balanced Salt Solution by tailoring the intermetallics' morphology in the as-extruded state. The results showed that the wires from ultrasound-treated ingots corroded faster than non-treated ones in immersion for up to 6 hours. This trend shifted for longer periods, and ultrasound-treated material showed lower corrosion rates and uniform corrosion, while the non-treated material displayed localized corrosion signs. Tensile testing of the wires demonstrated that immersion in EBSS lowered the tensile strength and elongation at fracture due to material degradation, regardless of the processing route. Nonetheless, this decline was sharper in the non-treated material. These findings suggest that ultrasound melt processing can be a promising method for improving the corrosion resistance of magnesium-based materials, paving the way for their use in manufacturing biodegradable stents. [ABSTRACT FROM AUTHOR]

Mechanical stretching is experienced ubiquitously by human tissues and their constituent cells and impacts biochemical and (mechano)biological processes relevant to health and disease. Numerous cell-stretching devices (CSDs) have been developed and used to apply mechanical strain to cells and tissues in in vitro settings, however, few have shown compatibility with live-cell microscopy. In most microscopy-compatible CSDs, imaging is performed post-mechanical stretching while live-cell imaging during cyclic stretching is very rarely shown, especially at high stretching frequencies and for long experiments (i.e., hours long). Live-cell imaging during cell stretching has revealed distinct time-dependent biomechanical features of cells, such as cell fluidization at high amplitudes or frequencies, or cracking followed by recovery of cell monolayers. Basic human functions such as breathing and digestion require mechanical stretching of cells and tissues. However, when it comes to laboratory experiments, the mechanical stretching that cells experience in the body is not often replicated, limiting the biomimetic nature of the studies and the relevance of results. Herein, we establish the importance of mechanical stretching during in vitro investigations by reviewing seminal works performed using cell-stretching platforms, highlighting important outcomes of these works as well as the engineering characteristics of the platforms used. Emphasis is placed on the compatibility of cell-stretching devices (CSDs) with live-cell imaging as well as their limitations and on the research advancements that could arise from live-cell imaging performed during cell stretching. [ABSTRACT FROM AUTHOR]

The high saturation magnetic flux density, low coercivity, and high permeability of iron-based amorphous alloys make them excellent magnetic core materials for electrical devices. Their local embrittlement and high fracture strength, however, make them difficult to machine. To overcome these difficulties, we have developed a new machining method with optimized heat treatment to improve the machinability of amorphous alloys. We conducted a series of blanking tests on melt-spun and post-annealed Fe–Si–B–Cr amorphous alloys with as-quenched, relaxed, partially or fully crystallized, and grain-grown microstructures. SEM examinations of the fractured surfaces of the blanked specimens and TEM observations revealed that the blanking resistance and overall machining performance correlated with these microstructures. The as-quenched sample showed the largest blanking resistance, and the fracture surface exhibited a drooped top edge, vertical marks, and the formation of horizontal voids, suggesting that plastic deformation occurred. For the samples annealed up to 763 K, the blanking resistance decreased and fractographic examination indicated that the blanking occurred in a brittle manner. Annealing at higher temperatures (773–873 K) increased the blanking resistance and changed the fracture morphology, exhibiting intragranular and intergranular fractures of crystalline precipitates. After complete crystallization, several burrs appeared at the bottom of the sample. Annealing at 1073 K led to a further decrease in blanking resistance related to the intergranular fracture of large grains. The plastic deformation of the sheet deteriorated the blanking quality. Based on these findings, the optimum microstructure and post-treatment of the amorphous alloy for ideal blanking performance are proposed. [Display omitted] • We propose a novel blanking method using the transformation of amorphous alloys. • Blanking surfaces yield five characteristic shapes depending on the microstructure. • Machinability improves when crystals are dispersed in the amorphous phase. • Excessive crystallization deteriorates blanking quality. [ABSTRACT FROM AUTHOR]

The repair and remanufacturing industry is a key contributor to the green technological revolution in manufacturing. Laser Directed Energy Deposition (LDED) is one of the most suited techniques for remanufacturing complex 3-D parts. The localized repair of a free-form component requires the nozzle to be inclined, which can affect the deposition process and the bonding strength. Once repaired, the functional performance of the restored part strongly depends upon the quality of the bond between deposition and substrate. Typically, the determination of bonding strength involves using epoxy for carrying out the tensile test or machining the deposition to carry out shear tests, which are not very effective in determining the bonding strength of ultra-high strength depositions like CPM 9V steels used in remanufacturing. Hence, a novel 'tapered key in a slot' specimen is specially designed to measure the bonding strength of high-strength depositions. The effect of various LDED parameters on the bonding strength of the deposits has been characterized via a designed experiment. Detailed fractography of the failed specimens exhibited three distinct failure patterns: melt interface (MI), deposit-substrate interface (CSI), and deposit cross-section (CC). MI failures occur at low deposition heights and low melt depths. CSI failures are observed at higher deposition heights, and low melt depths and CC failures occur above a critical combination of deposition height and melt depth. These specimens were analyzed for residual stresses, material composition, and porosity. The most prominent failure pattern MI (∼63%) could be attributed to a synergistic effect of peak tensile residual stresses, a sharp transition in the concentration of hard vanadium carbide particles, and intergranular porosity. Based on this study, a set of process recommendations has been developed for sustainable remanufacturing. [Display omitted] • Developed a novel 'tapered key in a slot' technique for determining bonding strength of ultra-hard deposits via DED. • Fractography studies of failed keys identified three primary bonding failure modes: MI, CC and CSI. • Intergranular porosity, residual stresses, and VC concentration were investigated in the dpeosition and substrate. • MI mode occurs most frequently due to a synergistic interaction of residual stresses, VC diffusion, and micro-cracks. [ABSTRACT FROM AUTHOR]

To improve the processibility of high-volume fraction SiC p /Al composites and reduce the surface defects after machining, a machining method of laser-ultrasonic vibration assisted machining (L-UVAM) were presented in this paper. Aiming to study the mechanism of material deformation and surface formation in L-UVAM, a finite element model (FEM) of L-UVAM was developed and the corresponding experiments were conducted. The results combined simulation and experiments revealed that particle fracture, interface failure and crack propagation were the main forms of material deformation, and the support of the matrix for particles was weakened because of the softening effect caused by laser heating, which makes it easier for the tool to push particles distribution along the shear plane. In addition, the failure of the particles depended on its relative position to the tool. Compared with traditional machining, the surface quality of L-UVAM was better, and there were fewer broken particles and defects in the processed surface. The results obtained by simulation are in close agreement with cutting experiments. Therefore, L-UVAM can be applied in efficient machining of SiC p /Al composites. [ABSTRACT FROM AUTHOR]

Cold sintering is a chemo-mechanical densification process which allows densification of ceramics at low temperatures below 300 °C. This substantial reduction in the sintering temperature is enabled by an externally applied pressure and a compatible transient liquid phase. In this paper, ZnO is cold sintered using various commercial organic acids: formic, acetic and citric acid. The effect of these different transient phases on densification, microstructural evolution and mechanical response is investigated. Fourier transform infrared spectroscopy, thermogravimetric analyses and transmission electron microscopy were conducted to explain the chemical interactions in the cold sintering process. High relative densities (∼ 96 %) were achieved by formic and acetic acid, whereas poor densification was obtained for citric acid (< 80 %), despite the higher expected solubility of zinc oxide. The higher biaxial strength found in samples sintered with formic acid compared to acetic acid (i.e. ∼90 MPa vs. ∼40 MPa) is discussed supported by fractographic analyses. [ABSTRACT FROM AUTHOR]

Ductility collapse is a stubborn issue for developing high-strength aluminum (Al) matrix composites reinforced with graphene nanosheets (GNSs). In order to solve this problem, here we introduced large amount of in-situ alumina nanoparticles (∼3 vol%) into the GNSs/Al composite to boost its dimple fracture capability. Microstructural characterization showed that the introduced alumina nanoparticles were α-Al 2 O 3 with a diameter of ∼30 nm, which were distributed uniformly on the Al matrix. Tensile tests revealed that the composite possesses a high tensile strength of 464 MPa and appreciable amount of ductility (8.9%), the combination of which was superior to those in literatures. Fractographic analysis suggested that the in-situ alumina nanoparticles acted as nucleation sites for dimples and enabled strain-delocalization, leading to enhanced plastic deformability. An analysis on strengthening mechanisms further confirmed the synergistic reinforcing effect of ex-situ GNSs and in-situ alumina nanoparticles. These findings may provide guidance for promoting the mechanical properties of GNSs/Al composites. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of this study was to fractographically examine clinically fractured fixation screws used to fix implant supported restorations and to estimate stress at failure. 20 clinically fractured titanium implant fixation screws were collected and analyzed under scanning electron microscope in order to locate critical crack origin and calculate stress at fracture. Principles of fractographic analysis were applied using relative equations and cause and conditions of screw fracture were calculated. X-rays and patients' records were collected after approval of necessary consent forms. Fractographic analysis revealed location and dimensions of critical crack size for every fractured screw examined. Two patterns of screw fracture were identified; the first was related to improper seating of fixation screw leading to damage at screw threads and eventual fracture of screw body. The second was related to slow crack growth propagation causing final fracture of screw body. The calculated stress at failure ranged from 755 to 804 MPa. Patients' records revealed that 75% of fractured screws were related to single unit screw retained restorations. Single unit screw retained restorations and improperly seated implant abutments impose high stress concentration on fixation screw which may result in fixation screw fracture. [ABSTRACT FROM AUTHOR]

This paper presents an upset geometry sequence capable of providing strain loading paths from uniaxial compression to biaxial stretching. Combination of digital image correlation and experimental force vs. time evolutions allows determining the fracture strains and the instantaneous slope of the strain loading paths at the instant of cracking in principal strain space. Fractography using scanning electron microscopy helps identifying the crack opening modes corresponding to the different fracture strains. Results show that the proposed upset geometry sequence allows creating a new testing methodology for bulk forming similar to that of sheet forming with the widely used Nakajima test. [ABSTRACT FROM AUTHOR]

In the present study, the fatigue response of an additive manufactured H13 type hot-work tool steel is investigated across the High Cycle Fatigue (HCF) and Very High Cycle (VHCF) regimes. The primary focus encompasses the interpretation of fatigue strength models, the defect type analysis along with a detailed examination of crack initiation and growth mechanisms. Despite the tremendous development in AM technology, experimental data regarding advanced mechanical properties, and particularly fatigue behavior, are still limited. Here, microstructural analysis of a modified AMed H13 hot-work tool steel, a combination of HCF and VHCF testing methodologies implemented for the characterization of the fatigue behavior, as well as a thorough fractographic analysis of the fractured surfaces were performed. Results are compared with historical data of a conventionally ingot cast and forged grade to assess the influence of the AM process on the fatigue response of H13 hot-work tool steels. It proves to be comparable to the conventionally manufactured grade, showcasing the potential utilization of AM in the production of components used in high-demanding applications, and in hot work tooling applications. However, the type of critical defects identified in the AM grade was found to be process-induced, emphasizing the need to optimize process parameters to reduce both the number and size of defects and also to ensure component reliability and high performance in various industrial applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Digital image correlation method is appropriate for evaluating final stress distribution. • Artificial notches at the centerline of inwardly bent sections showed failure. • Stage II is governed by a medium stress intensity factor and hydrogen-enhanced fatigue. • High stress intensity factor governs Stage III crack growth. • Stress gradient in the depth direction is a significant feature of circumferential NNpH-CF. Circumferential near-neutral pH corrosion fatigue (C-NNpH-CF) occurs when the external surface of a buried pipeline is simultaneously subjected to both axial residual stresses and applied cyclic loads while exposed to a near-neutral pH corrosive environment. The crack advance during C-NNpH-CF occurs through several stages: incubation, Stage I (crack initiation and early-stage crack growth), Stage II (sustainable crack growth), and Stage III (rapid crack propagation leading to rupture). This study aims to investigate the combined impact of bending residual stress (an appropriate source of axial residual stress) and cyclic loading (simulated pipeline pressure fluctuations) on C-NNpH-CF failure. Stress distribution was analyzed using the digital image correlation (DIC) method. At the same time, crack growth stages were examined by fractographic images under the influence of the variation of different test parameters, including cyclic loading, initial notch depth and position, and bending angle. In addition to striation analysis, Crack Mouth Opening Displacement (CMOD) and Electron Backscatter Diffraction (EBSD) analysis were employed to gain a deeper understanding of the C-NNpH-CF failure mechanism. Under the influence of maximum bending angle and axial cyclic loading, failure could occur at the bent centerline in the inward direction of the bent pipeline, where the maximum tensile stress occurs on the external surface. A high stress intensity factor governs Stage III crack growth compared to Stage II crack growth, which is governed by a medium stress intensity factor and hydrogen-enhanced fatigue. The stress gradient in the depth direction of a bent pipeline, a significant feature of C-NNpH-CF, affects crack growth rate at different stages. [ABSTRACT FROM AUTHOR]

• 58.2 % reduction in the pore diameter and 31.8% enhancement in the tensile strength was achieved during the combined parametric impact. • A 90° torch angle demonstrates a bridging transfer method that creates a uniform layer of deposit. • The ideal TS of 65 cm/min eliminates the flaws including slag, cracks, and pits. • A high amount of molten metal is deposited at the maximum wire feed rate of 7 m/min, which causes larger-sized pores to develop. • The development of defects, such as slag, pits, and undercuts, serves as the promoter for the spread of cracks. Even though Wire and Arc Additive Manufacturing (WAAM) of the Al5356 component has garnered attention for making affordable, large-scale components, problems with porosity, humping, and undercut still exist. Therefore, optimising process parameters is crucial to achieving flawless products with consistent layer deposition. Hence in this research, the most important WAAM parameters including travel speed (TS), wire feed speed (WFS), and torch angle (TA), were examined in order to determine how they affected structural integrity while taking into account key responses such as porosity, pore diameter, and tensile strength. The Significance of Criteria Weighted Aggregated Sum Product Assessment (WASPAS) in conjunction with Intercriteria Correlation (CRITIC) was used to investigate the favourable circumstances and confirm that the TA is the most important parameter in the nucleation of pores. The verification studies demonstrate that a 58.2 % reduction in pore diameter results in a 31.8 % increase in tensile strength. An ideal TS and WFS of 65 cm/min and 5 m/min, with a maximum TA of 90°, were found to be the favorable conditions for printing Al5356 wall with a minimum porosity of 0.037 %, enhanced ultimate tensile strength of 278 MPa, and minimum pore diameter of 93 µm, according to the CRITIC associated WASPAS approach. Additionally, using the fractography, the damage process based on the porosity creation was investigated. The optimal parameters for generating a defect-free multi-layer structure were identified, hence enhancing the structure's suitability for industrial use. [ABSTRACT FROM AUTHOR]

In this study, the optimal carbon fiber/matrix (CF/matrix) interfacial adhesion was explored by tailoring sintering pressures, aiming to enhance the ultimate tensile strength (UTS) of CF/Mg composites. With increasing the pressure, the interfacial shear strength (IFSS) gradually increased from 28.8 MPa to 43.6 MPa. Remarkably enhanced UTS (152 MPa) of the composite was achieved, which was 120.3 % higher than that of the matrix, through optimizing the IFSS to 39.7 MPa. Correspondingly, the main failure mechanism was fiber pulling-out and direct fiber-cutting. Whereas, excessive IFSS (43.6 MPa) deceased the UTS of the composite, with the dominant failure mechanism of direct fiber-cutting. [Display omitted] • The CF/matrix interfacial adhesion was effectively optimized for enhanced mechanical properties of CF/Mg composites. • With an optimal interfacial adhesion, remarkable enhanced UTS (152 MPa) was achieved, which was 120.3 % higher than matrix. • An optimal interfacial adhesion contributed to effective load transfer and more harmful energy absorption at the interface. [ABSTRACT FROM AUTHOR]

Si 3 N 4 + SiO 2 based wave-transparent ceramics are popular due to their excellent hardness, good flexural strength, and superior dielectric properties. A recent study explored the use of compression molding to produce green pellets, followed by sintering. However, further investigation into the friction, wear, and water erosion characteristics should be explored to provide the final shape on the green and sintered pellets. Therefore, this study investigates the friction, wear, and water erosion behaviour of Si 3 N 4 + SiO 2 ceramic green compact GP1 and GP2 (compression molded at 305 MPa and 1912 MPa, respectively) and their sintered pellets SP1 and SP2 (sintered at 1500 °C). The wear and friction behaviour of the green pellets were studied under various loads (5 N and 10 N), while the sintered samples were tested at 5, 10, and 20 N, using ball-on-disk tribology in dry sliding conditions. The results show that the wear rate rises with an increase in the applied load. GP1 showed a high wear rate (165.0 ×10−4 mm3/N m), coefficient of friction (COF) of 0.36, and lower Hertzian contact stress (2.49 ×107 N/mm2) under 10 N load. Additionally, GP1 exhibited a higher erosion rate (143.61 mm3/min) with continuous erosion traces. In contrast, the sintered ceramics SP2 had an insignificant wear rate (4.55 ×10−4 mm3/N m) and erosion rate (15.83 mm3/min) with discontinuous erosion traces due to having higher hardness. Fractographic analysis showed that the primary wear mechanisms were abrasive wear, grain pull-out, crack propagation, debris formation, and surface fatigue. Additionally, the wear debris size decreased from green to sintered ceramics. HRTEM results confirmed the non-stoichiometric composition of mixed phases (Si 3 N 4 , SiO 2 , SiC, and Si 2 N 2 O) in the wear debris of both samples SP1 and SP2. In water jet erosion, the primary wear mechanisms identified were crack propagation, particle pull-out, striations, delamination, brittle fracture, and crater formation. [Display omitted] • Tribology and water jet erosion indicate shaping green compacts as a feasible alternative for wave-transparent ceramics. • Tribology showed green compacts had more wear and larger debris, while sintered samples had less wear and finer debris. • Water jet erosion caused cracks, striations, delamination, brittle fracture, and distinct crater formation. • Green ceramics had higher wear and continuous erosion; sintered ceramics had minimal wear and discontinuous erosion. • HRTEM revealed non-stoichiometric phases (Si3N4, SiO2, SiC, Si2N2O) in wear debris of sintered ceramics. [ABSTRACT FROM AUTHOR]

This paper explores the effect of the binder phase on the mechanical strength of room temperature fabricated (RTF) SrTiO 3 ceramic composites. Lithium molybdate-strontium titanate (Li 2 MoO 4 -SrTiO 3) and sodium silicate-strontium titanate (Na 2 SiO 3 -SrTiO 3), along with their corresponding single-phase materials, were investigated. A comparison with single-phase high temperature sintered counterparts was also conducted. The biaxial strength of RTF Na 2 SiO 3 -SrTiO 3 was seven times higher than that of Li 2 MoO 4 -SrTiO 3 composites (i.e. 77 MPa to 11 MPa), resulting in ca. 40 % of the strength of single-phase SrTiO 3 sintered at high temperature (i.e. ∼200 MPa). The relatively high strength of RTF Na 2 SiO 3 -SrTiO 3 is related to the polycondensation of (SiO 4)4- monomers in Na 2 SiO 3 aqueous solution. This yields stronger bonding of Na 2 SiO 3 with SrTiO 3 , as evidenced by wettability tests, supported by spectroscopy and fractographic analyses. The understanding of how the binder phase affects densification of ceramics fabricated at room temperature may lead to functional ceramic composites with enhanced structural integrity. [ABSTRACT FROM AUTHOR]

• Deep-learning based microstructural analysis of ductile cast iron fracture surfaces. • Mask R-CNN model trained for graphite particle detection using SEM images. • Fracture surface topography restored using 4-quadrant BSE signal. • Key parameters as particle size, shape, and distance extracted accurately. • Subsequent probabilistic simulation of crack resistance curves. This study investigates the deep-learning based microstructural analysis from SEM images of ductile cast iron fracture surfaces. A Mask R-CNN model was trained, achieving 70% precision and 75% recall in graphite particle detection. Combined with a fracture surface reconstruction using the. 4-quadrant backscattered electron signal, key parameters, including the particle size, shape and distance were extracted accurately. Compared to micrograph analysis, following probabilistic simulations showed the impact of the higher microstructural variance for the fracture surfaces on crack initiation, leading to higher scatter and elevated crack resistance curves. This highlights the potential of deep-learning based analysis for comprehensive microstructural characterization. [ABSTRACT FROM AUTHOR]

This study investigates the effect of microstructural variations on the mechanical properties of CuZn35Mn2Al1Fe1-C-GS brass alloy. Specimens taken from positions with different cooling rates in a large cast component exhibit coarse-grained (approximately 5 mm) and fine-grained (approximately 1 mm) microstructures. Fine-grained samples demonstrate at least a 7% increase in Ultimate Tensile Strength (UTS) and up to a 33% higher long crack threshold Δ K th,lc . Hardness measurements are similar between microstructures. The NASGRO model and cyclic R-curve are applied to fit crack propagation data, and fractographic analysis reveals distinct fracture mechanisms. The results indicate that a fine-grained microstructure enhances tensile strength and crack resistance, providing valuable insights for the design and maintenance of heavy machinery components made from cast brass. [Display omitted] • Cyclic fracture mechanical characterization of CuZn35Mn2Al1Fe1-C-GS brass. • Fine-grained microstructure enhances tensile strength by at least 7%. • Cyclic R-curves indicate a +33% rise in alternating Δ K th,lc for fine-grain brass. • Provides NASGRO and cyclic crack resistance fit parameters for two microstructures. • Fracture analysis shows reduced intercrystalline proportion in coarse-grain samples. [ABSTRACT FROM AUTHOR]

• LCF tests on high-strength rebars assess effects of pitting corrosion and high temperatures. • Modeled Gaussian pit morphology leads to analytical stress concentration model. • Identifies fractography augmented factors contributing to faster fatigue failure in corroded rebars. • Corroded rebar softens faster under fatigue, requiring fewer cycles to reach the same level. • Corroded rebars lose upto 91 % of their energy dissipation capacity from 400 to 700 °C. Fatigue of high-strength high-ductility steel rebars under pitting corrosion and high-temperature remains largely unknown, specifically concerning temperature-dependent pit sensitivity effects, limiting their widespread adoption despite advantages. This study performs high-temperature, low-cycle fatigue tests on Fe 500D rebars with Gaussian pits. Moreover, experimental results are compared with average strain energy density method, augmented with fractography-based, temperature-dependent parameter models, including exponential pit sensitivity function. Results show accelerated cyclic softening, with up to 94% and 91% reductions in fatigue life and energy dissipation capacity in corroded rebars, respectively. The findings enhance fatigue life predictions, aiding the design of more resilient and safer structures. [ABSTRACT FROM AUTHOR]

• The early failure of an AISI316L C-type Bourdon tube from a pressure gauge was investigated. • The microstructure in the failure zone was suspected of sensitization and exhibited intergranular corrosion. • The most probable cause of the early failure was an improper welding that causes the sensitization of the microstructure in the HAZ. This paper presents the failure analysis of a C-type Bourdon tube made of AISI 316L stainless steel, which was part of a pressure gauge. For the study, chemical composition and microstructure of the Bourdon tube were determined. Additionally, electrochemical attack with oxalic acid was used to asses if the microstructure was suspected of sensitization in samples taken near to and away from the failure. Finally, fractographic analysis of the failed Bourdon tube was accomplished by scanning electron microscopy. The results showed that the failure was due to an intergranular corrosion phenomenon that embrittled the material in the area close to the welding between the Bourdon tube and the joint. [ABSTRACT FROM AUTHOR]

• A typical composite failure of an inter-shaft bearing inner ring is reported. • The failure root cause and mechanism of the fractured bearing inner ring is proposed. • Numerical simulations are performed considering multi-physical loads and failure time sequence. • Reasonable improvement measures to avoid this type of composite failure are proposed. The inter-shaft bearing is a critical component in dual rotors aero-engine. Due to the complex and severe loads caused by the interactive excitation of HP and LP rotors during operation, the inter-shaft bearing is prone to damage accumulation and failure. Focusing on a typical failure of inter-shaft bearing inner ring fragmentation and cannot be spliced together completely in high thrust-weight ratio turbofan engine, this paper conducted morphological investigation, fractographic analysis, vibration signal processing, finite element numerical simulation, and fully studied the failure mechanism of this failure. The results indicated that: there exists an uncoordinated resonance speed of the HP rotor in close proximity to the operating speed. This puts the rotor in non-synchronous procession state, accompanied by the uncoordinated angular displacement of the inner and outer rings, which resulting in a lager rolling dynamic load in bearing inner ring. This further leads to high tangential impact load at the root fillet of the anti-rotation pin, causing significant stress concentration, and eventually leads to the generation of initial cracks. These cracks persist and propagate into fatigue oblique fracture over time. After oblique fracture, the modal frequencies of the inner ring become more dispersed. Under the rolling dynamic load (traveling wave load), nodal diameter vibration occurs, causing high stress vibration fatigue damage, and ultimately leading to multiple-point simultaneous fragmentation. The investigation suggests that reducing the stress levels at the root fillet of the anti-rotation pin of the inner ring is an effective approach to prevent bearing failure. This can be achieved through two methods: one is optimizing the rotor structure to decrease the rolling dynamic load on the inner ring, the other is eliminating the anti-rotation pin and appropriately reducing the tightening torque of the compression nut and the interference between the bearing inner ring and the HP turbine rear journal. [ABSTRACT FROM AUTHOR]

• Component-like specimen reproducing EDM and STEM drilling on a turbine bucket. • Detrimental effect of EDM drilling on high-temperature HCF. • Competitive effects of surface roughness and microstructural alteration on HCF. • Non-propagating cracks from the EDM recast layer. The paper deals with the effects of electrochemical and electro-discharge deep hole drilling on the high-temperature fatigue behavior of a directionally solidified GTD-111 superalloy. High-temperature HCF tests were carried out at 800 °C on specimens having a coaxial hole drilled with the investigated processes. The hole diameter and length were 1.5 and 95 mm, respectively. The material's high-temperature HCF S-N curve was also obtained to provide a reference curve. Despite the scatter caused by the material microstructure in the fatigue crack nucleation and propagation regime, the fatigue strength was found to be affected by the investigated hole drilling techniques. The electro-discharge deep hole drilling was found to lower the fatigue strength by 8%. Fractographic analyses showed that it can be attributed to the different hole surface roughness and microstructural alteration in the underlying material. [ABSTRACT FROM AUTHOR]

• Neither ageing severity nor layups have effects on mode I fatigue delamination. • Ageing severity and layups have negligible influence on material degradation and fatigue delamination mechanisms. • This study provides extra information for ISO mode I fatigue delamination test standard development of composite laminates. Ageing is known to have significantly detrimental effect on mode I fatigue delamination growth (FDG) in unidirectional (UD) composite laminates. However, composite structures are usually designed with multidirectional (MD) layups, which raises the question that is it enough to only conducted fatigue delamination experiments on specimens with a UD layup. The aim of this study is therefore to explore mode I FDG in MD composite laminates with 45//45 interface after different ageing, i.e. at 70 °C 85 % relative humidity (RH) and immersion in 70 °C water bath. Fatigue delamination experiments were conducted at stress ratios R = 0.1 and 0.5. The fatigue data, interpreted via Paris-type fatigue laws, demonstrated that: (1) the change of ageing severity has no influence on mode I FDG in MD composite laminates; (2) FDG remains the same in composite laminates after different ageing, regardless of layups. In all cases, the same master resistance curves can be obtained to determine the intrinsic mode I fatigue delamination resistance of UD and MD composite laminates after different ageing. The physical reasons for these findings were discussed based on the moisture content analysis, Fourier transform infrared (FTIR) analysis, dynamic mechanical thermal analysis (DMTA), and fractographic examinations. It was found that material degradation and delamination mechanisms remain the same for UD and MD layups, as well as for 85 %RH and water bath conditioning. [ABSTRACT FROM AUTHOR]

In the Arctic, the fatigue properties of marine steels under low temperatures and complex loads are essential for the safety of ship navigation. In this study, the fatigue crack growth (FCG) characteristics of EH36 and EQ70 steels are explored under low-temperature mixed mode (I + II) through experiments and numerical simulation. Experimental results show that the FCG life and the crack growth retardation (CGR) effect of both steels correlate positively with the loading angle and negatively with the temperature. The prediction results for FCG path indicate that the Maximum Tangential Stress (MTS) criterion provides accurate predictions for loading angles less than 45° in low-temperature mixed mode (I + II), while the Richard model is more suitable for the loading angle of 60°. The simulation results show that, when the crack deflects, K II decreases rapidly in magnitude while K I gradually increases and becomes dominant. The SEM results for the FCG fracture surfaces in both steels revealed that the roughness of the fracture surface is positively correlated with the loading angle, moreover clear transition regions are observed between the pre-crack and crack growth regions. • The FCG life of EH36 and EQ70 steels positively correlates with loading angles. • A transition region exists before the crack deflection. • The MTS criterion is more accurate to predict FCG path at 30° and 45°. • Low-temperature mixed-mode loading triggered a crack growth retardation effect. • The fracture roughness of both steels correlates positively with loading angle. [ABSTRACT FROM AUTHOR]

• Fracture toughness assessment of decommissioned reactor pressure vessel weld metal. • Use of miniature compact tension specimens to determine reference temperature. • Effects of thermal ageing and irradiation in weld metal are investigated. • Fractography is performed to gain insights into brittle crack initiation sites. This paper investigates the fracture toughness of thermally aged and irradiated weld metals extracted from head and beltline regions of a decommissioned nuclear reactor pressure vessel. Miniature compact tension specimens are fabricated from the thermally aged reactor pressure vessel head weld as well from the circumferential and axial beltline welds having fluences of 2.90 × 1016n/cm2 and 7.94 × 1017n/cm2, respectively. Master curve approach in accordance with the ASTM E1921 is applied to determine the reference temperature T 0 and it is found to be − 113.5 °C, −104.4 °C, and − 89.3 °C for the reactor pressure vessel head, axial beltline, and circumferential beltline welds, respectively. In addition, the multimodal reference temperature T m to assess the homogeneity of welds as well as key curve analysis for the quality assurance of testing are also provided. Fractographic analysis identified variations in crack initiation sites and microstructural inhomogeneities, particularly in the irradiated beltline welds. Overall, fracture mechanical testing of the materials demonstrated that miniature compact tension specimens are effective for characterizing the fracture toughness of limited surveillance weld materials, revealing differences due to irradiation and weld location. [ABSTRACT FROM AUTHOR]

• Fatigue crack extension of an 18% Ni martensitic steel. • Crack propagation comprised crack initiation ahead the crack tip and coalescence. • Three kinds of mode-type in fatigue crack extension based on material behavior. • Damage accumulation mode embodied special fractography and crack configuration. • Material index from crack extension mode-type to propose evaluation method. The fatigue properties of martensitic steels tend to differ significantly from those of low- and medium-strength steels. Even if the hardness is the same, the fatigue strength varies substantially depending on the microstructure. Thus, for using martensitic steel rationally and developing materials with high fatigue strength, it is desirable to establish a fatigue strength evaluation method that can consider the microstructural effects on fatigue properties. For this purpose, 18% Ni bcc martensitic steel was used as a model metal to conduct rotating-bending fatigue tests in this study. The fatigue crack behavior on the smooth specimen surface was examined, and the fracture surface morphology on both sides of the broken specimen and the microplastic strain distribution near the fatigue crack tip were analyzed. The results clarified the mechanism underlying fatigue crack extension (FCE). The analytical results revealed three types of FCE mechanisms dependent on the stress amplitude, stress state (i.e., plane stress or plane strain), and martensitic microstructure. Considering these mechanisms, a unique stress–life curve was predicted, and a particular fatigue crack shape and fractography were confirmed. The material indices were speculated to be the representative properties of martensitic steels. [ABSTRACT FROM AUTHOR]

• Tensile and Charpy impact tests on armor steel are performed across a wide range of loading rates. • The ability of the material models J-C and R-K as well as the modified J-C model, (MJ-C model), to capture material behaviour in the impact range is being investigated. • The simulated and experimental results are compared. • The fracture surface is analysed, and the results are correlated. The amount of energy that can be absorbed by armor steel during dynamic loadings, such as a crash, impact, or blast, is crucial. To characterize the behaviour of material deformation under such loading, rigorous testing and a suitable material model are needed. Within the scope of this research, relevant tensile tests in the dynamic range are carried out to obtain the parameters necessary for three different material models, namely, the Johnson-Cook (J-C), Rusinek and Klepaczko (R-K), and a newly proposed modified Johnson-Cook (MJ-C) model. Tensile tests are simulated using these three material models, and the results are compared with the experimental results. The Charpy impact test at five different striking velocities, viz. 3, 4, 5, 6, and 8 ms−1 are numerically simulated using these material models. Upon comparing the obtained results with the experimental data, it becomes evident that the J-C model with modification (MJ-C) exhibits the best fit in prediction with regard to the specimen energy absorption and force versus displacement. A fractography investigation is also carried out to estimate the number of voids and void size with striking velocities. It shows that at higher strain rates, the number of voids increases. Additionally, the plastic deformation is restricted at high strain rates, leading to higher stress and reduced ductility. [ABSTRACT FROM AUTHOR]

• Fatigue crack growth tests were performed for multiple overload ratios and multi-step loading. • Having two overloads prior to initiation proves more effective in improving fatigue life than having only one. • Fractography of all the tested specimens was carried out using FE-SEM. • Surface roughness of the fractured specimens was measured using a 3D profilometer. • Microstructural analysis at the crack path was characterized by EBSD methods. An experimental study was conducted to examine the initiation of cracks in the AZ31B magnesium (Mg) alloy for tensile overload effects, exploring the influence of overload cycle number, magnitude, and multiplicity of the applied overloads (OL). The number of cycles to failure increased from 8 % to 15 % for overload ratio (OLR) of 1.5 and 2.0 respectively applied as first cycle when compared with constant amplitude loading (CAL). However, the number of cycles to failure increased from 25 % to 43 % for OLR of 1.5 and 2.0 respectively when overload was applied at 5000th cycle. The onset of cracks was delayed when two overloads were applied as the first and 5000th loading cycles. The longitudinal-transverse (L-T) specimens were tested using a two-step high-low sequence loading procedure by varying maximum and minimum load. The fractography results also depict variations in the initial crack formations under different overload conditions. The effects of different overloads on the fracture surfaces of Compact Tension specimens were examined using the Field Emission Scanning Electron Microscopy, indicating substantial reduction in both the number and size of microcracks. 3D profilometer tests were performed, indicating a surface roughness of 0.20 μm to 0.30 μm. [ABSTRACT FROM AUTHOR]

• Fatigue crack growth behavior of AZ31B magnesium alloy under different load ratios. • Fatigue tests were performed for varying temperatures ranging from 300 K , 373 K and 473 K. • Fractography of all the tested samples were carried out using Field Emission Scanning Electron Microscopy (FE-SEM). • The surface roughness of the fractured samples was measured using a 3D-profilometer. First ever fatigue crack growth experiments were conducted under various load ratios (R = 0.1 to 0.8) at 300 K , and (R = 0.1, 0.3, 0.5, and 0.7) at 327 K and 473 K , respectively, on AZ31B magnesium alloy. The results reveal that temperature-dependent variations in both fatigue crack growth rates and stress intensity factor ranges (Δ K) across different load ratios. It was found that at relatively higher load ratio (R = 0.8) leads to a lower Δ K = 8.0287 MPa√m and a lower load ratio (R = 0.1) result in a higher Δ K = 15.5981 MPa√m, indicating that the material undergoes fatigue crack propagation at a higher level of stress intensity factor range at room temperature. A slower crack propagation was seen at higher load ratio (R = 0.8), whereas lower load ratio (R = 0.1) exhibits faster crack growth at 300 K. Similarly, crack growth generally increases at higher temperatures (i.e., 373 K and 473 K). The fatigue life of the magnesium alloy AZ31B increased from 12,410 to 87,031 cycles at 300 K , 9,620 to 32,667 cycles at 373 K , and 9,140 to 30,143 cycles at 473 K as the load ratio increases. The average fatigue life decreases to 59 % and 63 % as the temperature is varied from 300 K through 373 K to 473 K. The fractographic and surface roughness carried out by field emission scanning electron microscopy and 3D-Profilometer respectively, illustrate that roughness of fracture surfaces correlates with an increase in the fatigue crack growth rate for a specific value of Δ K. [ABSTRACT FROM AUTHOR]

In this paper, the entire fracture surface approach was used to assess an effect of 280,000 h of exploitation under internal pressure of 2.9 MPa and high temperature of 540 °C on the fatigue response of 10H2M (10CrMo9–10) power engineering steel. The mechanical testing was carried out on the hourglass specimens produced from the as-received, unused pipeline and the same material after long-time exploitation. The uniaxial tensile tests were performed to establish the stress amplitude for subsequent force controlled, fatigue testing in the range from ±250 MPa to ±400 MPa under the frequency of 20 Hz. Since the exploited 10H2M steel was characterized by significantly lower mechanical properties, different damage mechanisms responsible for specimen failure were revealed through fracture surface analysis. The fracture surface topography evaluation was performed with a 3D non-contact measuring system. It was found, that the exploitation state has a strong impact on the fatigue life and fracture characteristics since the significant drop in lifespan of about 300 %–400 % was found for the material after prolonged service. Finally, the proposed surface topography parameter was related to the stress amplitude in order to estimate the fatigue life for the steel in question. • The effect of the long-term exploitation (280,000 h/2.9 MPa/540 °C) on the fracture surface was assessed. • Surface parameters were evaluated for entire fracture areas of 10H2M steel specimens. • The relationship between fracture surface topography parameters and stress amplitude was analysed. [ABSTRACT FROM AUTHOR]

• 0.75 m/s velocity and 200 MPa pressure are found to be fail-safe for pin-roller assembly. • The roller's principal stress transitions from compressive to tensile, at higher velocities. • The hertz stress for the pin-roller-track contacts matches well with the FE model findings. • The bottom roller and pin of the bucket wheel excavator fails due to static overloading. • The failure mode of pin and roller are ductile and mixed-mode, respectively. Mining excavators play a crucial role in the mining industry, and their reliable operation depends on the integrity and efficiency of various components, including rollers and pins. This study presents a comprehensive analysis of mining (Bucket wheel) excavator rollers and pins, aiming to understand their structural characteristics (load capacity and structural integrity), performance, deformation, and failure behaviour as well as potential areas of improvement. The study investigates the performance aspects of excavator rollers and pins in terms of their ability to withstand compressive pressure forces employing Finite Element Modelling (FEM). Numerical studies, in conjunction with experimental validations, are found to be capable of determining stress distribution as well as failure criteria of bottom roller and pin. A thorough quasi-static analysis has been conducted, considering the real-world operating conditions of the excavator. The simulation findings are found to be helpful towards extending maintenance windows, decreasing failures, and improving the roller and pin system efficiency. FE simulations reveal that increased velocity significantly raises von Mises stress and contact pressure, with the highest values at 1.0 m/s, and causes the roller's principal stress to shift from compressive to tensile. Optimal operational parameters are found to be excavator roller translational velocity of 0.75 m/s and an applied pressure load of 200 MPa. Whereas metallographic, chemical analysis, and mechanical characterisation of the failed roller and pin samples establishes the metallurgical reasons of failure of roller-pin assembly, apart from confirming accuracy of the simulation findings. Also, the strain softening from dynamic and static overloading is identified as the main cause of failure mechanism. Fracture surface analysis shows ductile failure in pins and mixed-mode fracture in rollers. [ABSTRACT FROM AUTHOR]