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Mechanoluminescent materials, which emit light in response to elastic deformation, are demanded for use as in situ stress sensors. ZnS doped with Mn is known to exhibit one of the lowest reported thresholds for appearance of mechanoluminescence, with repeatable light emission under contact pressure

A novel computational approach to predicting fatigue crack initiation life in additively manufactured microlattice structures is proposed based on a recently developed microplasticity-based constitutive theory. The key idea is to use the concept of (micro)plastic dissipation as the driving factor to model fatigue degradation in additively manufactured metallic microlattice. An ad-hoc curve-fitting procedure is proposed to calibrate the introduced material constitutive parameters efficiently. The well-calibrated model is employed to obtain fatigue life predictions for microlattices through a diverse set of RVE-based finite element fatigue simulations. The model's predictive capabilities are verified by comparing the simulation results with experimental fatigue data reported in the literature. The overall approach constitutes a unified setting for fatigue life prediction of additively manufactured microlattice structures ranging from low- to high-cycle regimes. It is also shown that the model can be applied to technologically relevant microlattices with mathematically-created complex microstructure topologies. [ABSTRACT FROM AUTHOR]

Strain localization is a significant issue that poses interesting research challenges in viscoelastic materials because it is difficult to accurately predict the damage evolution behavior. Over time, the damage mechanism in the amorphous structure of viscoelastic materials leads to subsequent localization into a shear band, gradually jeopardizing the materials' elastic sustainability. The primary goal of this study is to further understand the morphological effects and the role of shear bands in viscoelastic materials precipitated by strain localization. The current study aims to consolidate the various failure mechanisms of a sample and its geometry (surface-to-volume ratio) used in torsional testing, as well as to understand their effects on stress relaxation durability performance. A torsional shear load stress relaxation durability test was performed within the elastic region on an isotropic viscoelastic sample made of silicon rubber and a 70% weight fraction of micron-sized carbonyl iron particles. Degradation was caused by a shear band of localized plasticity that developed microscopically due to stress relaxation durability. The failure pattern deteriorated as the surface-to-volume ratio decreased. A field-emission scanning electron microscope (FESEM) and a tapping-mode atomic force microscope (AFM) were used for further observation and investigation of the sample. After at least 7500 cycles of continuous shearing, the elastic sustainability of the viscoelastic materials microstructurally degraded, as indicated by a decline in stress performance over time. Factors influencing the formation of shear bands were observed in postmortem, which was affected by simple micromanipulation of the sample geometry, making it applicable for practical implementation to accommodate any desired performance and micromechanical design applications. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomers (MREs) are well-known for their ability to self-adjust their mechanical properties in response to magnetic field influence. This ability, however, diminishes under high-strain conditions, a phenomenon known as the stress-softening effect. Similar phenomena have been observed in other filled elastomers; hence, the current study demonstrates the role of fillers in reducing the effect and thus maintaining performance. Anisotropic, silicone-based MREs with various carbonyl iron particle (CIP) concentrations were prepared and subjected to uniaxial tensile load to evaluate high-strain conditions with and without magnetic influence. The current study demonstrated that non-linear stress–strain behavior was observed in all types of samples, which supported the experimental findings. CIP concentration has a significant impact on the stress–strain behavior of MREs, with about 350% increased elastic modulus with increasing CIP content. Microstructural observations using field emission scanning electron microscopy (FESEM) yielded novel micro-mechanisms of the high-strain failure process of MREs. The magnetic force applied during tension loading was important in the behavior and characteristics of the MRE failure mechanism, and the discovery of microcracks and microplasticity, which was never reported in the MRE quasi-static tensile, received special attention in this study. The relationships between these microstructural phenomena, magnetic influence, and MRE mechanical properties were defined and discussed thoroughly. Overall, the process of microcracks and microplasticity in the MRE under tensile mode was primarily formed in the matrix, and the formation varies with CIP concentrations. [ABSTRACT FROM AUTHOR]

Tensile and compressive pre-yield mechanical behavior of a rolled AZ31 Mg alloy sheet was studied by cyclic loading–unloading tests along rolling direction (RD) and transverse direction (TD). The results show that the mechanical response of pre-yielding is not linear elasticity. Microplasticity with irreversible strain and energetic dissipation is observed during tension. While anelasticity with reversible strain and dissipative energy is detected during compression. A stress dependent varied elastic modulus model was built by introducing a stress factor to capture the asymmetric behavior. Three model parameters are tensile yield strength, initial elastic modulus and critical modulus at tensile yield point. Consequently, this model is verified by comparison with the experimental observations. The anelastic and micro-plastic deformation are ascribed to the glide of mobile dislocations. The asymmetric behavior of tension and compression is clarified by the nucleation mechanism of {10–12} twinning. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomers (MREs) are well-known for their ability to self-adjust their mechanical properties in response to magnetic field influence. This ability, however, diminishes under high-strain conditions, a phenomenon known as the stress-softening effect. Similar phenomena have been observed in other filled elastomers; hence, the current study demonstrates the role of fillers in reducing the effect and thus maintaining performance. Anisotropic, silicone-based MREs with various carbonyl iron particle (CIP) concentrations were prepared and subjected to uniaxial tensile load to evaluate high-strain conditions with and without magnetic influence. The current study demonstrated that non-linear stress–strain behavior was observed in all types of samples, which supported the experimental findings. CIP concentration has a significant impact on the stress–strain behavior of MREs, with about 350% increased elastic modulus with increasing CIP content. Microstructural observations using field emission scanning electron microscopy (FESEM) yielded novel micro-mechanisms of the high-strain failure process of MREs. The magnetic force applied during tension loading was important in the behavior and characteristics of the MRE failure mechanism, and the discovery of microcracks and microplasticity, which was never reported in the MRE quasi-static tensile, received special attention in this study. The relationships between these microstructural phenomena, magnetic influence, and MRE mechanical properties were defined and discussed thoroughly. Overall, the process of microcracks and microplasticity in the MRE under tensile mode was primarily formed in the matrix, and the formation varies with CIP concentrations.

Traditional fracture theories infer damage at cracks (local field) by surveying loading conditions away from cracks (far field). This approach has been successful in predicting ductile fracture, but it normally assumes isotropic and homogeneous materials. However, myriads of manufacturing procedures induce heterogeneous microstructural gradients that can affect the accuracy of traditional fracture models. This work presents a microstructure‐sensitive finite element approach to explore the shielding effects of grain size and crystallographic orientation gradients on crack tip microplasticity and blunting. A dislocation density‐based crystal plasticity model conveys texture evolution, grain size effects, and directional hardening by computing the constraint from dislocation structures. The results demonstrate that the microstructure can act as a buffer between the local and far fields that affects the crack tip microplasticity variability. For nominal opening loading, grain size and texture affect the local ductility and induce a non‐negligible multiaxial plastic deformation. Furthermore, driving forces based on measuring displacements away from the crack tip are less affected by the microstructure, which suggests that traditional experimental methods smear out important crack tip variability. [ABSTRACT FROM AUTHOR]

The structure and physical and mechanical properties of a 17GS steel specimen cut from a main gas pipeline section under use for over 50 years at a working pressure of 5.5 MPa is investigated in this study. The pipe under study laid in a straight-line segment and covered with sand was in service according to regular parameters. Metallography studies using methods of optical and scanning microscopy for analyzing transformations in the crystal structure of the metal are carried out. Mechanical tests are focused on the impact strength and static tension to determine changes in the physical and mechanical properties. The data obtained are compared with the as-delivered state specified by the manufacturer, currently accepted standards and industry requirements for pipes intended for reuse. The research reveals the basic mechanical characteristics of the steel to be virtually the same as those stated by the manufacturer; no structural transformations in the metal are found. The principal degradation process in the specimen of interest is identified to be sub-surface corrosion occurring no deeper than 100 µm. from the result of this study is that changes in the structure and mechanical properties appear insignificant over 50 years of service provided that the maximal stress in the pipes is below the limit of macroelasticity. [ABSTRACT FROM AUTHOR]

The enhancement of fracture toughness exhibited by silica glass (SG) remains a challenge for a wide variety of technology applications, particularly without implying significant changes in the glass structure. The present work shows that embedded platinum nanoparticles (PtNPs) can significantly improve the mechanical performance of silica glass (PtNPs/SG). The PtNPs were implanted into a high‐purity SG substrate with 3MV Tandem accelerator Pelletron and thermally annealed at 600°C. Rutherford backscattering spectroscopy and transmission electron microscopy characterizations disclosed a Gaussian distribution of PtNPs at 600‐nm depth. Nanoindentation test revealed that brittleness (B) decreased about 24% and the effective elastic modulus (Er) increased by about 7% for the nanostructured compound. Additionally, an increase in fracture toughness (Kc) of 19% and an enhancement of elasto‐plastic performance behavior during the scratch test were observed. Therefore, embedded PtNPs represent a potential solution for brittleness problems in SG. [ABSTRACT FROM AUTHOR]

The objective of this work is to present analytical solutions for several 2D model problems to demonstrate the unique plastic fields generated by the implementation of micromorphic approach for gradient plasticity. The approach is presented for finite deformations and several macroscopic and nonstandard microscopic boundary conditions are applied to a gliding plate to illustrate the capability to predict the size effects and inhomogeneous plastic fields promoted by the gradient terms. The constitutive behavior of the material undergoing plastic deformation is analyzed for softening, hardening and perfect plastic response and corresponding solutions are provided. The analytical solutions are also shown to match with the numerical results obtained by implementing a user element subroutine (UEL) to the commercial finite element software Abaqus/Standard. [ABSTRACT FROM AUTHOR]

Gradient structures have excellent mechanical properties, such as synergetic strength and ductility. It is desirable to reveal the connection between the gradient structure and mechanical properties. However, few studies have been conducted for materials with heterogeneous dislocation distribution. In the present study, we use the discrete dislocation dynamics (DDD) method to investigate the effect of dislocation density gradient on the elastoplastic behavior of single crystals controlled by source activation. In contrast to the intuitive expectation that gradient structure affects the mechanical properties, the DDD simulations show that the elastic moduli and yield stresses of three gradient samples (i.e., no gradient, low gradient, and high gradient) are almost identical. Different from the progressive elastic–plastic transition in the samples controlled by Taylor hardening (i.e., the mutual interaction of dislocation segments), the flow stresses of source activation ones enter into a stage of nearly ideal plasticity (serrated flow) immediately after yielding. The microstructure evolution demonstrates that the mean dislocation spacing is relatively large. Thus, there are only a few or even one dislocation source activated during the plastic flow. The intermittent operation of sources leads to intensive fluctuation of stress and dislocation density, as well as a stair-like evolution of plastic strain. The present work reveals that the effect of dislocation density gradient on the mechanical response of crystals depends on the underlying dislocation mechanisms controlling the plastic deformation of materials. [ABSTRACT FROM AUTHOR]

Single-crystalline cast aluminium microwires with a diameter near 15 are characterised by Laue microdiffraction. A microwire in the as-cast condition exhibits a misorientation below over a length of 500. The measured density of geometrically necessary dislocations is low, m−2, though local maxima up to one order of magnitude higher are found. After tensile deformation to failure, the dislocation density is significantly increased in microwires that have mostly deformed in single slip (m−2), and yet higher when deformation has occurred by multiple slip (m−2). In deformed single slip oriented microwires, the streaking directions of Laue spots show that dislocations are stored (though not exclusively) on the primary slip system. Results are consistent with a deformation mechanism governed by rotating, likely single-arm, sources. [ABSTRACT FROM AUTHOR]

The objective of this work is to present analytical solutions for several 2D model problems to demonstrate the unique plastic fields generated by the implementation of micromorphic approach for gradient plasticity. The approach is presented for finite deformations and several macroscopic and nonstandard microscopic boundary conditions are applied to a gliding plate to illustrate the capability to predict the size effects and inhomogeneous plastic fields promoted by the gradient terms. The constitutive behavior of the material undergoing plastic deformation is analyzed for softening, hardening and perfect plastic response and corresponding solutions are provided. The analytical solutions are also shown to match with the numerical results obtained by implementing a user element subroutine (UEL) to the commercial finite element software Abaqus/Standard.

The amplitude-dependent internal friction in carbon fiber reinforced plastic (CFRP) laminates subjected to fatigue cycling has been measured and analyzed to convert into the plastic strain of the order of 10-8 as a function of effective stress. The microplastic flow indeed occurs in the stress range three orders of magnitude lower than the failure stress, and the stress-strain curves tend to shift to a lower stress as the number of cycles increases, thus indicating a decrease in the CFRP strength. The microflow stress at the plastic strain of 1×10-8 keeps a constant value of about 0.4 MPa in the range less than 103 cycles but then decreases gradually, whereas the Young's modulus evaluated from the resonant frequency is almost constant up to 104 cycles where only transverse cracks are found. Thus we can successfully detect the onset of fatigue deterioration by means of the amplitude-dependent internal friction.

The influence of the physicochemical characteristics of the tempering medium on the structure of nickel samples is studied. The micromechanisms of plastic hardening and fracture of the surface layer under friction are established. The temporal changes in strength characteristics of the metal surface layer at the initial stages of friction load are determined. These strength characteristics have a cyclic character. The duration of the cycle of strength characteristics strongly depends on the tempering medium. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to develop a unifying energy approach for rapid assessment of fatigue parameters in high-cycle fatigue regime. The energy dissipation is considered as an index of fatigue damage to analyze the progressive microstructural movements and to evaluate the fatigue behavior of low-carbon steel (e.g. residual life and microplasticity). A set of theoretical and experimental works are performed to demonstrate its applicability. The relationships between the predicted fatigue parameters and the traditional testing results are compared and discussed. It is concluded that the present approach is applicable for macro and micro high-cycle fatigue behavior evaluation. [ABSTRACT FROM AUTHOR]

An energetic method is proposed to rapidly evaluate the macro- and microfatigue behavior of aluminum alloy in highcycle fatigue. The theoretical correlation between the thermal signal and the energy dissipation during the fatigue process is established for the irreversible dissipation mechanism description. The energetic method is applied to predict the fatigue strength and the entire fatigue life of the aluminum alloy. Moreover, the energy dissipation is properly used to evaluate the microplastic behavior at the grain scale, which is responsible for the progressive movements of the internal microstructures. Experiments were carried out to validate the current energetic method, and good agreement was obtained between the predicted results and the traditional results. Thus, the current energetic method is confirmed to be promising for the macro and micro high-cycle fatigue behavior assessment. [ABSTRACT FROM AUTHOR]

• The microplasticity and macroplasticity behavior of additively manufactured Al-Mg-Sc-Zr alloys before and after aging were examined. • A combination of In-situ synchrotron X-ray diffraction and full-field crystal plasticity modeling was employed. • The micromechanical behavior of both as-built and direct-aged specimens includes several sub-stages. • The predicted macro stress-strain curves, lattice strains, and dislocation densities from CPFFT modeling agree with In-situ measurements. • The plastic deformation pattern is more heterogeneous in the direct-aged specimen due to the presence of Al 3 (Sc , Zr) particles. Understanding and controlling the performance of additively manufactured aluminum alloys containing scandium (Sc) and zirconium (Zr) elements heavily relies on knowledge of their microplasticity and macroplasticity behavior. However, this aspect has received very little attention. In this investigation, we examined the microplasticity and macroplasticity behavior of additively manufactured Al-Mg-Sc-Zr alloys before and after aging, using in-situ synchrotron X-ray diffraction and full-field crystal plasticity modeling. Our study provides a quantitative assessment of the transitions from elasticity to microplasticity and then to macroplasticity and analyzes the development of the initial microstructure, particularly the dislocations. We constructed crystal plasticity fast-Fourier-transform models based on dislocation densities. The predicted evolutions of macroscopic stress-strain curves, lattice strains, and dislocation densities agree with in-situ measurements. The present findings provide deep insights into controlling the performance of AM Al-Mg-Sc-Zr alloys. Besides, the micromechanical model developed in this investigation paves the way for predicting the microplasticity and macroplasticity behavior of various metallic materials. [ABSTRACT FROM AUTHOR]

We have studied the structural transformations and deformation behavior of an amorphous AlNiLa alloy during nanoindentation and uniaxial tension tests and assessed the influence of crystalline phases resulting from lamp processing and heat treatment. Our results confirm the high effectiveness of lamp processing: at identical phase compositions, the lamp processing time is shorter by more than two orders of magnitude. The microplasticity of the amorphous alloy has been shown to manifest itself in both nanoindentation and uniaxial tension tests. The high proportion of local plasticity in the work of indentation has been accounted for in terms of possible intercluster sliding. The observed lamp processing- and heat treatmentinduced changes in the hardness of the alloy reflect changes in its phase composition and the percentages of the amorphous and crystalline phases, which does not rule out a cluster mechanism of local deformation or its deceleration by nanocrystalline phases in the amorphous-nanocrystalline structure. [ABSTRACT FROM AUTHOR]

The strengthening mechanism of graphene in graphene/Cu nanolaminated composites was investigated by progressive compressive stress relaxation experiments in the microplastic regime. The results reveal that, when the loading effect of graphene is lacking, the higher yield strength of the composite is attributed to the higher long-range internal stress and effective stress at the yield point. The derived activation volumes imply a much higher critical resolved shear stress required for dislocation cross-slip and/or nucleation at/near grain boundaries in the graphene/Cu composite than that in the unreinforced Cu matrix, indicating that graphene may significantly affect the intrinsic deformation mechanism of the matrix. [ABSTRACT FROM AUTHOR]

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This paper is concerned with an application of full-field calorimetric method for the microplasticity evaluation in the very high cycle fatigue regime. The employed method is essentially based on the establishment of an experimental energy balance during the fatigue process. It allows the estimation of the plastic strain of very low magnitude produced by cyclic slip, which is considered as the primary mechanism of the ultrahigh cycle fatigue in the face-centered cubic materials. By the developed method, the plastic strain amplitudes of a polycrystalline copper in the very high cycle fatigue regime are estimated, and its relationship with the fatigue lives is established via the Manson-Coffin law. [ABSTRACT FROM AUTHOR]

We have studied the mechanical properties and corrosion resistance of an amorphous FePSiMnVC alloy and their response to nanocrystallization as a result of brief lamp processing and heat treatment. The results demonstrate that the lamp processing time needed to obtain a given phase composition through partial crystallization of the amorphous alloy is two orders of magnitude shorter than the corresponding heat treatment time. We have found lamp processing conditions that ensure the formation of an amorphous-nanocrystalline composite with a twofold increase in hardness, without loss of plasticity. It has been shown that, with increasing loading rate during nanoindentation, the hardness of the alloy decreases because of the increase in plasticity, which shows up as the formation of a larger number of shear bands. Under uniaxial tension, the material exhibits microplasticity, which may be due to intercluster sliding, with the amorphous structure retained. The corrosion resistance of the as-prepared amorphous alloy in a medium contaminated with sulfur dioxide exceeds that of the partially crystallized alloys. [ABSTRACT FROM AUTHOR]