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Polymeric composites find extensive usage in aerospace applications, and their performance is influenced by environmental conditions throughout their life cycle. This study focuses on assessing the performance of composite laminates under different environmental conditions to evaluate the load carrying capacity (LCC) due to delamination. The laminates were specifically designed to withstand high pressure and temperature, ensuring satisfactory performance throughout their service life. The specimens, prepared according to ASTM standards with a thickness of 3 mm, featured different fibre orientations between the upper and lower laminates, including 0/0°, 0/30°, 0/45°, and 0/60°. The change in the delamination growth behavior for specimens subjected to different initial delamination lengths (a0) was studied using pre and post-radiographic tests (RT). The investigation encompassed a range of initial delamination lengths, from 70 mm to 110 mm, incremented by 10 mm. Notably, failure was observed in specimens with a 0/30° angle when the initial crack length (a0) reached 110 mm, while specimens with a 0/60° angle failed at an initial crack length of 80 mm. Additionally, it was noted that the maximum force required for the 0/30° angle laminate was observed when the initial crack length was 70 mm. [ABSTRACT FROM AUTHOR]

Strength prediction under the action of pores is crucial for the safety of ceramics. Here, a quantitative prediction model of pore-strength response under mode-I loading was developed based on the new mapping relationship between stress intensity factor and tip radius. The new model was proved to have great application after comparison and analysis of the pore-strength test data of three typical ceramics as well as the pertinent data as-reported in the literature. Results indicated that when the tip radius of pore (ρ) exceeds the critical value (ρ c = K Ic 2/(π σ 0 2)), the stress intensity factor increases as a power function with increasing ρ , at which point the strength decay is significantly weakened, and when the ρ is lower than the ρ c , the pore can be equated to a crack problem. This work can not only forecast and assess the failure strength of ceramics containing pores, but also provide guidance for the design of extremely dependable ceramics. [ABSTRACT FROM AUTHOR]

The analysis of FGM structures requires the implementation of sophisticated mechanical behavior simulation tools, and the interaction between design and manufacturing and the risks associated with cracks play an important role in understanding the mechanical behavior of crack structures. The effect of cracking on the functional gradient plate was studied in this research. In our study and for damage tolerance insurance, the stress intensity factor was determined for the purpose of predicting the behavior of cracked structures similar to the examples studied i.e. type of combination of FGM materials, type of applied load and type of crack, the numerical evaluation of this factor is determined using the displacement extrapolation technique (DET) and the generalized displacement correlation method (GDC) in an APDL (Ansys Parametric Design Language) numerical code to prove the evolution, the continuous variations of the material properties are incorporated by specified parameters at the centroid of each element. The crack growth paths with different FGM gradient parameters under mechanical and thermal loads are investigated and compared with reference solutions. The current DET, GDC, and reference solution results are in good agreement. [ABSTRACT FROM AUTHOR]

Context: At the interface of W-Cu after direct jointing, diffusion layers with a thickness of approximately 22 nm are present but often overlooked in simulations of mechanical properties. In this study, an interface model with a W-Cu diffusion layer is developed using molecular dynamics (MD). The effects of the diffusion layers on the elastic–plastic behaviors, dissipation mechanisms, and fracture properties of the interface are analyzed under mode-I (perpendicular to the interface) and mode-II (parallel to the interface). The results demonstrate that the interface model with a diffusion layer exhibits superior mechanical properties under mode-I and mode-II loading compared to the model without a diffusion layer. Furthermore, a multi-scale method based on the classical Paris law is proposed, combining MD and finite element methods to investigate the fatigue crack propagation of W-Cu bimetallic composites under cyclic loading and predict their fatigue life. The findings of this study are meaningful for improving the mechanical properties of W-Cu interface materials, predicting the material's lifespan, and guiding related engineering applications. Methods: In this study, the molecular dynamics simulations have been carried out by using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). The visualization of results is performed using the Open Visualization Tool (OVITO). Common neighbor analysis (CNA) and dislocation analysis (DXA) in OVITO have been employed to capture the structural evolution. Finite element method simulations are performed in Ansys Workbench. [ABSTRACT FROM AUTHOR]

Mechanically, composite laminates perform exceptionally well in-plane but poorly out-of-plane. Interlaminar damage, known as "delamination," is a major issue for composite laminates. Results from Mode-I and Mode-II experimental testing on twill-woven carbon fiber reinforced (CFRP) laminates are analyzed in this paper. Composite Mode-I fracture toughness was determined using three different methods in accordance with ASTM D5528: modified beam theory, compliance calibration, and a codified compliance calibration. Two methods, the Compliance Calibration Method and the Compliance-Based Beam Method, were used to determine the Mode-II fracture toughness in accordance with ASTM D7905. Stick-slip behavior is quite evident in the composite's Mode-I fracture toughness test findings. The MBT technique's GIc values for initiation and propagation are 0.533 and 0.679 KJ/m2, respectively. When comparing the MBT approach to the industry-standard ASTM procedure for determining fracture toughness Mode-I, the MBT method was shown to be highly compatible. Furthermore, the GIIc values for the CBBM technique are 1.65 KJ/m2 for non-pre cracked and 1.4 KJ/m2 for pre-cracked materials. The CBBM method shows a good method to evaluate fracture toughness Mode-II, due to not needing to monitor the length of the crack during delamination growth to get the value of the fracture toughness.

Mechanically, composite laminates perform exceptionally well in-plane but poorly out-of-plane. Interlaminar damage, known as "delamination," is a major issue for composite laminates. Results from Mode-I and Mode-II experimental testing on twill-woven carbon fiber reinforced (CFRP) laminates are analyzed in this paper. Composite Mode-I fracture toughness was determined using three different methods in accordance with ASTM D5528: modified beam theory, compliance calibration, and a codified compliance calibration. Two methods, the Compliance Calibration Method and the Compliance-Based Beam Method, were used to determine the Mode-II fracture toughness in accordance with ASTM D7905. Stick-slip behavior is quite evident in the composite's Mode-I fracture toughness test findings. The MBT technique's GIc values for initiation and propagation are 0.533 and 0.679 KJ/m², respectively. When comparing the MBT approach to the industry-standard ASTM procedure for determining fracture toughness Mode-I, the MBT method was shown to be highly compatible. Furthermore, the -IIc values for the CBBM technique are 1.65 KJ/m² for non-pre cracked and 1.4 KJ/m² for pre-cracked materials. The CBBM method shows a good method to evaluate fracture toughness Mode-II, due to not needing to monitor the length of the crack during delamination growth to get the value of the fracture toughness. [ABSTRACT FROM AUTHOR]

Tissue mimicking materials are designed to represent real tissue in applications such as medical device testing and surgical training. Thanks to progress in 3D-printing technology, tissue mimics can now be easily cast into arbitrary geometries and manufactured with adjustable material properties to mimic a wide variety of tissue types. However, it is unclear how well 3D-printable mimics represent real tissues and their mechanics. The objective of this work is to fill this knowledge gap using the Stratasys Digital Anatomy 3D-Printer as an example. To this end, we created mimics of biological tissues we previously tested in our laboratory: blood clots, myocardium, and tricuspid valve leaflets. We printed each tissue mimic to have the identical geometry to its biological counterpart and tested the samples using identical protocols. In our evaluation, we focused on the stiffness of the tissues and their fracture toughness in the case of blood clots. We found that the mechanical behavior of the tissue mimics often differed substantially from the biological tissues they aim to represent. Qualitatively, tissue mimics failed to replicate the traditional strain-stiffening behavior of soft tissues. Quantitatively, tissue mimics were stiffer than their biological counterparts, especially at small strains, in some cases by orders of magnitude. In those materials in which we tested toughness, we found that tissue mimicking materials were also much tougher than their biological counterparts. Thus, our work highlights limitations of at least one 3D-printing technology in its ability to mimic the mechanical properties of biological tissues. Therefore, care should be taken when using this technology, especially where tissue mimicking materials are expected to represent soft tissue properties quantitatively. Whether other technologies fare better remains to be seen., (© 2024 Wiley Periodicals LLC.)

• The CCNBD of sandstone was employed to study mode-I fracture behaviors under cyclic loading. • 3D discrete element model of CCNBD specimen was built. • A modified fracture toughness calculation method was proposed. • The effect of cyclic loading on microstructure characteristics and FPZ was discussed. To study the mode-I failure and mechanical behavior of rock under cyclic loading, the cracked chevron notched Brazilian disc (CCNBD) of sandstone was employed in this paper, and thus three different upper-limit loads cyclic tests were carried out, including 95 %SUL(static ultimate load) ∼ 35 %SUL, 85 %SUL ∼ 25 %SUL, 75 %SUL ∼ 15 %SUL. The 3D discrete element model of CCNBD specimen was built to study mechanical properties and cracking behavior at a meso -scale. Meanwhile, the effect of cyclic loading on microstructure characteristics and fracture process zone (FPZ) was discussed. The results show that cyclic loading has a weakening effect on fracture toughness, and a modified fracture toughness calculation method was proposed considering the effect of irreversible plastic deformation under cyclic loading. There are obvious stages of microcracking behavior under cyclic loading, specific for the condition of 85 %SUL ∼ 25 %SUL, and the microcrack density is positively correlated with the number of cycles. Meanwhile, the effect of cyclic load on sandstone microstructure contains weak-structure fracture effect and compaction effect, and they exist simultaneously and work together. In addition, cyclic loading has a great influence on the length of FPZ, and the length of FPZ under cyclic loading is greater than that under monotonic loading. [ABSTRACT FROM AUTHOR]

Effectiveness and durability of interventions on deficient concrete structures remain a major concern, comprising the challenge of old-to-new concrete compatibility and bonding, as stress concentrations and microstructural flaws at the old-to-new concrete interface compromise structural integrity and create migration paths for harmful contaminants. Fiber reinforcement can be beneficial, but proper quantification and mastering of fundamental mechanisms is required before these are fully utilized. A study is presented on Mode-I crack growth resistance at the interface between two concretes (substrate and repair). Countered Double Cantilever Beam tests are performed, crack growth resistance curves calculated (Modified Linear Elastic Fracture Mechanics), and complemented with analysis of interfacial roughness and failure planes. Polyvinyl alcohol (8 and 12 mm length) and steel fibers (13 mm) are introduced in the repairs at 0.5% and 1% volume fractions. Results indicate that fibers improve fracture behavior of both the repair material and substrate-repair interface; correlations with interfacial roughness, crack deviation, and fracture parameters are discussed. [ABSTRACT FROM AUTHOR]

The paper presents a new analytical model for thin structural adhesives in glued tube-to-tube butt joints. The aim of this work is to provide an interface condition that allows for a suitable replacement of the adhesive layer in numerical simulations. The proposed model is a nonlinear and rate-dependent imperfect interface law that is able to accurately describe brittle and ductile stress–strain behaviors of adhesive layers under combined tensile–torsion loads. A first comparison with experimental data that were available in the literature provided promising results in terms of the reproducibility of the stress–strain behavior for pure tensile and torsional loads (the relative errors were less than 6%) and in terms of failure strains for combined tensile–torsion loads (the relative errors were less than 14%). Two main novelties are highlighted: (i) Unlike the classic spring-like interface models, this model accounts for both stress and displacement jumps, so it is suitable for soft and hard adhesive layers; (ii) unlike classic cohesive zone models, which are phenomenological, this model explicitly accounts for material and damage properties of the adhesive layer.

Effectiveness and durability of interventions on deficient concrete structures remain a major concern, comprising the challenge of old-to-new concrete compatibility and bonding, as stress concentrations and microstructural flaws at the old-to-new concrete interface compromise structural integrity and create migration paths for harmful contaminants. Fiber reinforcement can be beneficial, but proper quantification and mastering of fundamental mechanisms is required before these are fully utilized. A study is presented on Mode-I crack growth resistance at the interface between two concretes (substrate and repair). Countered Double Cantilever Beam tests are performed, crack growth resistance curves calculated (Modified Linear Elastic Fracture Mechanics), and complemented with analysis of interfacial roughness and failure planes. Polyvinyl alcohol (8 and 12 mm length) and steel fibers (13 mm) are introduced in the repairs at 0.5% and 1% volume fractions. Results indicate that fibers improve fracture behavior of both the repair material and substrate-repair interface; correlations with interfacial roughness, crack deviation, and fracture parameters are discussed.

A recently reported solvent spraying technique was used herein for incorporation of multi-walled carbon nanotubes (MWCNTs) on unidirectional carbon fiber/epoxy prepregs. The role of the agglomerates reduction of oxidized MWCNTs on Mode-I interlaminar fracture toughness (GIC) of laminated composites was investigated using double cantilever beam tests. Multiscale laminate composites were fabricated using MWCNTs without and with an acid oxidation, agglomerates reduction (AR) and a sequential treatment based on oxidation and AR. For comparison, specimens without MWCNTs were also prepared and tested. Fourier transform infrared analysis shows evidence of an important amount of oxygenated functional groups on the surface of as-received and oxidized MWCNTs. The results also show Mode-I fracture toughness improvements for all the laminated composites compared to reference samples. A substantial 52% increase in the averageGICinitiation was achieved for laminated composites reinforced with oxidized AR-MWCNTs prepared with only 0.05 wt.% MWCNTs. [ABSTRACT FROM AUTHOR]

In this paper, molecular dynamics (MD) simulation deformation studies on the Al (metal)-CuZr (metallic glass) model interface is carried out based on cohesive zone model. The interface is subjected to mode-I loading at a strain rate of 10 s and temperature of 100 K. The dislocations reactions and evolution of dislocation densities during the deformation have been investigated. Atomic interactions between Al, Cu and Zr atoms are modeled using EAM (embedded atom method) potential, and a timestep of 0.002 ps is used for performing the MD simulations. A circular crack and rectangular notch are introduced at the interface to investigate the effect on the deformation behavior and fracture. Further, scale size effect is also investigated. The structural changes and evolution of dislocation density are also examined. It is found that the dominant deformation mechanism is by Shockley partial dislocation nucleation. Amorphization is observed in the Al regions close to the interface and occurs at a lower strain in the presence of a crack. The total dislocation density is found to be maximum after the first yield in both the perfect and defect interface models and is highest in the case of perfect interface with a density of 6.31 × 10 m. In the perfect and circular crack defect interface models, it is observed that the fraction of Shockley partial dislocation density decreases, whereas that of strain rod dislocations increases with increase in strain. [ABSTRACT FROM AUTHOR]

In the simulation of the ductile fracture process in a low ductility aluminum alloy, the limitations of the current implementation of a stress-state dependent cohesive model are identified. Ductile fracture data was generated at moderate triaxiality with experiments on a range of notched bars while at high triaxiality in growth of a pre-existing mode-I crack in compact test specimens. In the corresponding finite element analysis, cohesive elements obeying a stress-state dependent cohesive law were introduced in the plane where material separation was expected to occur. By recognizing that the effect of model parameters is decoupled in fracture at moderate triaxiality, a procedure is outlined to determine the unique combination of model parameters that is shown to reproduce the experimental data for the entire range of triaxiality well. It is argued that the necessity of a plane strain core and its thickness is largely driven by the extent to which plastic deformation spreads during the growth of crack. [ABSTRACT FROM AUTHOR]

• Mode-I failure modes of UD and TW CFRP laminates are analyzed and compared. • Failure is monitored using by simultaneous usage of AE and IRT techniques. • Four types of micro damage are identified by clustering AE hits. • Fiber and matrix dominant failures are related with distinctive thermal activities. • Hybrid monitoring of failure helped to interpret thermal activities effectively. Mode-I fracture toughness test provides valuable information in the thickness direction of fiber reinforced polymer matrix composites. However, damage propagation under mode-I loading is dependent on the configuration of reinforcing material of the laminate. Understanding the damage types and their growth rate in mode-I fracture toughness test is a vital factor to obtain material allowable for safe design. In this study, mode-I tests are conducted on unidirectional, and twill woven carbon fiber reinforced polymer composite laminates. A new approach is proposed to interpret passive infrared thermography results based on correlating acoustic emission and thermography results in time whereby thermal activities can be classified into two main groups corresponding to matrix and fiber dominant failure types. It is demonstrated that matrix and fiber dominant failures lead to thermal activities with line-wise and point-wise form, respectively. Results show that four different damage types can be seen for mode-I fracture of both laminates. The temporal observations during thermoelastic cooling of the materials show that twill woven laminate releases relatively higher energies due to matrix dominant damage developments which means this configuration type is more prone for delamination failures. [ABSTRACT FROM AUTHOR]

Modeling fracture with a cohesive zone model requires an appropriate cohesive law for correlating interfacial tractions and crack face separation, especially in mixed-mode loading scenarios. Various approaches have been employed in order to develop such a law which can be characterized into potential-based and non-potential-based formulations. A critical re-examination of these methods is presented here, followed by a novel mixed-mode formulation which satisfies a physical criterion for crack propagation. Specifically, as the crack propagates, the trailing current crack tip is defined through the vanishing of normal and tangential components of the interfacial tractions simultaneously. A general formulation for mixed-mode conditions is proposed in this paper. In particular, given normal and tangential traction separation laws for pure normal and tangential modes as being material properties, the normal and tangential traction separation laws in mixed-mode loading are formulated so that all traction components disappear at the same effective separation when the crack advances. The new mixed-mode law is used to analyze three standard fracture problems in laminated composites, including double cantilever beam (DCB), end-notch flexure (ENF), and mixed-mode bending (MMB). A comparison with predictions from some selected mixed-mode cohesive laws and experimental data available in the literature is also included to further validate the proposed mixed-mode law. [ABSTRACT FROM AUTHOR]

We performed classical molecular dynamics (MD) simulations to predict the strength of Al (metal)–Cu 50 Zr 50 (metallic glass) model interface at a temperature of 300 K and strain rate of 10 10 s − 1 under mode-I and mode-II loading conditions based on the cohesive zone model (CZM). EAM (Embedded Atom Method) potential is used for modeling the interaction between Al Cu Zr atoms. It is observed that the interface strength is higher than pure Al, and ruptures in the Al region by necking under mode-I loading. Atoms of Al stick to the Cu 50 Zr 50 metallic glass after fracture due to strong bonding between Al Cu and Al Zr atoms than Al Al atoms as inferred from density functional theory based study. The observed dominant dissipative mechanisms at the interface are partial dislocations and stair rod dislocations under both the loading conditions. The strength of the interface decreases in the presence of a crack as expected. The traction-separation response of the interface shows a maximum stress followed by a decrease in stress indicating the complete separation of the interface. The present study gives a significant insight into metal–metallic glass interface deformation behavior and underlying mechanism. The results can be input into continuum length-scale micromechanical models that determine overall material properties. [ABSTRACT FROM AUTHOR]

This article reports the results of numerical implementation of a recently proposed versatile cohesive law (TCZM) that incorporates triaxiality of the stress state explicitly in its formulation. TCZM was implemented numerically by devising user-defined elements in ABAQUS v 6.10 for a CT specimen geometry to replicate its fracture behavior as observed in experiments. The measured macroscopic force-deflection curve characteristics show a good agreement with the experimental observations, which illustrates the effectiveness of the TCZM. [ABSTRACT FROM AUTHOR]

Abstract: Assessment and evaluation of fracture characteristics are very important in adhesive joint for achieving a safety mode. In this paper, fracture was investigated in mode-I in adhesive composite material/aluminum alloy joints. To achieve this aim, Double Cantilever Beam (DCB) was used to evaluate fracture in mode-I loading (opening). Bonding was realized by epoxy adhesive as one of the most important and widely used adhesives in aerospace and automotive industries. Modified Beam Theory (MBT) and Compliance Calibration Method (CCM) were formulated to calculate Strain Energy Release Rate (SERR). The obtained experimental results were verified by comparison with Finite Element (FE) analysis. FE results were derived from using Virtual Crack Closure Technique (VCCT) and J-integral approaches in two and three dimension (2-D & 3-D) simulation. Experiment tests and numerical analyses showed good agreement and demonstrated the effectiveness of the proposed experiment and numerical methods. [Copyright &y& Elsevier]

We consider plane deformations of a linearly elastic solid in the case where either a mode-I or mode-II crack is present but, perhaps more significantly, when surface effects are included in the mechanics of the crack faces. The surface effects lead to a more accurate description of deformation and are incorporated using a version of the continuum based surface/interface model of Gurtin and Murdoch. We obtain a semi-analytic solution valid throughout the entire domain of interest (including at the crack tips) via two series of coupled Cauchy singular integro-differential equations which are solved numerically using an adapted collocation technique. It is shown that, among various other interesting phenomena, when the solid incorporates a traction-free crack face and is subjected to uniform far-field stresses (tension and in-plane shear), the surface effects result in the elastic response and corresponding stress fields being size-dependent. In particular, we note that, in contrast to classical linear elastic fracture mechanics, our model allows for finite stresses at the (sharp) crack tip. [ABSTRACT FROM AUTHOR]

Abstract: To enable the effective and reliable use of structural adhesive bonding in automotive applications, the cohesive properties of a joint need to be determined over a wide range of loading rates. In this paper, a strategy for determining these properties has been described and used to analyze a set of experimental results presented in a companion paper. In the particular system studied, a crack growing in a toughened quasi-static mode could make a catastrophic transition to a brittle mode of fracture. The cohesive parameters for both the toughened and brittle modes of crack growth were determined by comparing numerical predictions from cohesive-zone simulations to the results of experimental tests performed using double-cantilever beam specimens and tensile tests. The cohesive parameters were found to be essentially rate-independent for the toughened mode, but the toughness dropped by a factor of four upon a transition to the brittle mode. The results of wedge tests were used as an independent verification of the cohesive parameters, and to verify that the quasi-static properties remained rate-independent to very high crack velocities corresponding to conditions of low-velocity impact. The effects of friction, and the use of the wedge test to determine cohesive parameters, were also explored. [Copyright &y& Elsevier]

Abstract: Rate effects for adhesively-bonded joints in steel sheets failing by mode-I fracture and plastic deformation were examined. Three types of test geometries were used to provide a range of crack velocities between 0.1 and 5000mm/s: a DCB geometry under displacement control, a wedge geometry under displacement control, and a wedge geometry loaded under impact conditions. Two fracture modes were observed: quasi-static crack growth and dynamic crack growth. The quasi-static crack growth was associated with a toughened mode of failure; the dynamic crack growth was associated with a more brittle mode of failure. The experiments indicated that the fracture parameters for the quasi-static crack growth were rate independent, and that quasi-static crack growth could occur even at the highest crack velocities. Effects of rate appeared to be limited to the ease with which a transition to dynamic fracture could be triggered. This transition appeared to be stochastic in nature, it did not appear to be associated with the attainment of any critical value for crack velocity or loading rate. While the mode-I quasi-static fracture behavior appeared to be rate independent, an increase in the tendency for dynamic fracture to be triggered as the crack velocity increased did have the effect of decreasing the average energy dissipated during fracture at higher loading rates. [Copyright &y& Elsevier]

Conductive adhesives and filled adhesive systems, in general, are used in a variety of engineering applications. There are a number of issues of concern in the design of joints bonded using electronically conductive adhesives (ECAs) and subjected to cyclic loading. These include the effects of stress state and cyclic parameters (frequency and waveform) of mechanical and/or thermal loading on the fatigue failure behavior of adhesively-bonded joints. In order to study the effects of these parameters on joint behavior, two different joint geometries were designed and tested under a spectrum of fatigue and environmental conditions. The results of our work indicated a profound influence of the stress state and cyclic waveform type on the fatigue strength of the joints. Lowering the cyclic load frequency was also found to reduce the fatigue life of the bonded joints. [ABSTRACT FROM AUTHOR]

Conductive adhesives have been used in a variety of electronic packaging applications. This paper presents an investigation into the effects of various adherend surface treatments on the fatigue and failure behaviors of adhesively-bonded joints. For this purpose, single-lap joints were fabricated using specimens with adherend surfaces modified employing various chemical and mechanical modification techniques, and tested under a spectrum of fatigue and environmental conditions. The results of our work indicate a profound influence of the adherend surface on both the fatigue behavior and also the moisture ingress mechanism into the joint. Finally, experiments were conducted to assess the effect of adherend surface condition on the moisture ingress mechanism. [ABSTRACT FROM AUTHOR]

Experimental and numerical analyses are performed to determine the translayer mode-I fracture toughness of a thick-section fiber reinforced polymeric composite using the eccentrically loaded, single-edge-notch tension, ESE(T) specimen. Finite element analyses using the virtual crack closure technique were performed to assess the effect of material orthotropy on the mode-I stress intensity factors in the ESE(T) specimen. The stress intensity factors for the proposed ESE(T) geometry, are calculated as a function of the material orthotropic parameters. The formula is validated for a class of thick composite materials. The thick composite tested in this study is a pultruded composite material that consists of roving and continuous filament mat layers with E-glass fiber and polyester matrix materials. Data reduction from the fracture tests was performed using two methods based on existing metallic and composite ASTM [ASTM E 1922, Standard Test Method for Translaminar Fracture Toughness of Laminated Polymer Matrix Composites, Annual Book of ASTM Standards, 1997; ASTM E 399, Standard Test Method for Plane-Strain Fracture Toughness of Metallic Materials, Annual Book of ASTM Standards, 1997] fracture testing standards. Criteria for assessing test validity and for determining the critical load used in calculating the fracture toughness were examined. Crack growth measurements were performed to determine the amount of stable crack growth before reaching critical load. The load versus notch mouth opening displacement, for different crack length to width ratios is affected by material orthotropy, nonlinearity, and stable crack propagation. The mode-I translayer fracture toughness and response during crack growth is reported for ESE(T) specimen with roving layers oriented both, transverse and parallel to the loading direction. [Copyright &y& Elsevier]

Electronically-conductive adhesives (ECAs) have been used for electronics packaging applications. Today this technology is used in electronics for laptop computers, camcorders, watch electronics, hard-drive suspensions and in various other electronic equipments. Even though ECAs have excellent potential for being efficient and less costly alternative to lead-solder interconnects, they still possess a number of problems with respect to durability and design to meet specific needs. One of the issues that requires understanding is the fatigue behavior due either to mechanical or thermal stresses varying in a cyclic manner. This study intends to address the fatigue and failure behavior of ECAs under ambient operating conditions. For this purpose, joints were prepared using stainless steel adherend specimens bonded with a commercial ECA, and tested using monotonic and cyclic loadings at ambient environmental conditions (28°C and 20% relative humidity). S–N curves were generated using these specimens at four different load-ratios (R), namely 0.1, 0.3, 0.5, 0.7 and 150 Hz cyclic frequency. The S–N curves were not parallel, exhibited non-linear behavior with diminishing slope at higher R values. [ABSTRACT FROM AUTHOR]

Plain strain mode-I singular plastic fields are examined for cracks embedded in pressure sensitive solids. Material response is described by a small strain deformation theory in conjunction with elliptic yield criterion and plastic potential. Non-associativity is accounted for and a pure power law is assumed to characterize strain hardening. The material does not admit a strain energy function hence it is not possible to deduce a-priori the J-integral motivated stress singularities. A standard separation of variables representation of near-tip eigenfunctions has been evaluated numerically, over a range of material parameters. It has been found that stress singularities may deviate from J-integral predictions, with increasing non-associativity, by up to nearly 20%. Sample illustrations are provided for singular field profiles and some aspects of pressure sensitive non- associated plasticity are discussed. [ABSTRACT FROM AUTHOR]

A comprehensive stochastic analysis of pure and mixed mode interlaminar fracture of fibre-reinforced polymer (FRP) composites, using different uncertainty quantification approaches, is presented. The primary aim of this work is to evaluate the accuracy and computational cost of stochastic reduced order models in the finite element modelling of FRP composite fracture. The Monte Carlo method, with different sampling methods was considered as a reference method for comparison purposes. By comparing the descriptive statistics of uncertain quantities of interest, the advantages and drawbacks of these methods is revealed. Double Cantilever Beam (DCB), End Notch Flexure (ENF) and Mixed Mode Bending (MMB) tests were simulated using a stochastic cohesive zone model. Fundamental characteristics of the cohesive zone model, such as the interlaminar fracture toughness and cohesive strength, were assumed as uncertain sources, and crack extension and critical force were considered as uncertain quantities of interest. The use of a stochastic reduced order model combined with a surrogate model is shown to be computationally efficient, for a given level of accuracy, even with a limited number of samples. [ABSTRACT FROM AUTHOR]