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Advances in the use of in situ transmission electron microscopy (TEM) to study mechanical deformation have enabled a direct correlation of mechanical properties with microstructures, in particular, atomic-level defect dynamic processes. Shear deformation of metallic materials has been noticed to lead to unique microstructural features with superior properties that would be difficult to achieve by traditional metallurgical processes. However, in contrast to the case of in situ TEM studies of structural evolution under tension, compression, and bending, in situ TEM probing of dynamic processes during direct shear loading, especially at microscales and nanoscales, is very limited. This paper reviews recent progress on the development of in situ TEM for studying shear deformation in terms of both the technique and the scientific insights that have been gained. In addition, we discuss current challenges encountered in the use of in situ TEM for shear deformation, such as the limited total strain, strain rate, and spatial and temporal resolution. To provide perspective, we present promising opportunities for in situ TEM studies with pure shear loading by taking advantage of the integration of advanced imaging techniques both in TEM and scanning transmission electron microscopy domains, advanced electron detectors, highly efficient chemical analysis, data-driven machine learning, and environmental conditions. [ABSTRACT FROM AUTHOR]

Although tension-shear coupling of weave fabrics in large deformation has been observed in experiments, most constitutive models for weave fabrics often ignore this coupling effect for simplicity. In this paper, a nonlinear anisotropic hyperelastic constitutive model is proposed to consider this tension-shear coupling effect. Draping experiments of a plain weave fabric over a tetrahedron mold are carried out to validate the proposed coupling constitutive model. Subsequently, the influences of tension-shear coupling on draping processes are investigated. Numerical simulation results indicate that the tension-shear coupling effect significantly changes fiber reorientation during draping process, which makes shear deformation tend to be uniform and reduces the local shear deformation concentration and should not be neglected in woven fabric stamping with salient double curvatures. [ABSTRACT FROM AUTHOR]

A new method has been developed for measuring not only bending but also shear flexibility of pulp fibers by using confocal laser scanning microscopy. Based on the Steadman and Luner method, a two-stage wet pressing process was used which enabled both bending and shear flexibility and both bending and shear modulii of fibers to be determined with a single test. Three types of fibers, i.e., bleached spruce Kraft Pulp (BKP), aspen bleached chemi-themomechanical pulp (BCTMP), and aspen themomechanical pulp (CTMP), were tested. Results show that the longitudinal elastic modulii of the fibers are in a range of 3–37 GPa, and the transverse shear modulii of them are in a range of 27–103 MPa. It was also found that the shear contribution to the overall fiber deformation ranged from 60% to 90% for the fibers measured. This substantiates the concept of shear contribution to measured fiber flexibility as proposed by Waterhouse and Page. [ABSTRACT FROM AUTHOR]

The role of deformation twinning in the formation of a fine-grained structure in cold-rolled 310S steels has been investigated by using transmission electron microscopy. When 310S steels were rolled at room temperature, a deformation twin appeared in the early stage of the rolling process. A fine lamellar structure consisting of the deformation twin and matrix (T-M) developed with increased rolling strain. At moderate strain, micro shear bands appeared in the area of the T-M lamellar structure, and the shear bands grew and multiplied during further cold-rolling. Such multiplication of shear bands destroyed the T-M lamellar structure, which caused the development of a fine-grained structure. In shear bands, a highly misoriented structure with a submicron grain size was generated. In this paper, the mechanism of the transmutation process from the T-M lamellae into the fine-grained structure is discussed. Particular emphasis is laid on the role of deformation twinning in the formation of the fine-grained structure. [ABSTRACT FROM AUTHOR]

In this paper, the effect of thermal cycle on the interlaminate shear strength (ILSS) and impact behaviour of unidirectional carbon fibre reinforced polyetherimide (PEI) matrix composites were studied. Samples were subjected to 100 thermal cycles (by immersing from boiling water (100°C) to ice water (0°C). The effects of thermal cycles were characterized by short beam shear and instrumented impact testers. Also Fractographic investigations were done using a scanning electron microscope (SEM). It is observed that the plastic deformations at the fibre/matrix and interlaminar interface as well as residual stresses lower the ILSS and flexural modulus of the material proportional with the number of thermal cycles. Up to the first 20 thermal cycles the material shows a brittle fracture with lower fracture energy, but after the 20th thermal cycles it is possible to observe that the material fractures with higher fracture energy at longer fracture time. A remarkable difference in the fracture morphology between the thermal cycled and un-treated materials has been observed. It is found that thermal cycles strictly affect the fracture morphology. [ABSTRACT FROM AUTHOR]

A new grain fragmentation model is proposed for the formation of grain substructures in polycrystalline materials during plastic deformation. Micro-shear bands and twins are assumed to originate from grain boundaries due to the local stress concentrations caused by the interaction of grain boundaries and slip bands. These stress concentrations will impose shear fluctuations on the neighboring grains, which can be relaxed by the formation of corresponding substructures, i.e., micro-shear bands and twins, in these neighboring grains. Texture simulations for cold rolling and equal channel angular pressing (ECAP) of commercially pure titanium are performed using a combined approach of the viscoplastic self-consistent (VPSC) model and the shear fluctuation model. The texture update scheme in the combined approach is presented. Experimental textures at different thickness reductions of cold rolling at room temperature (300 K) and after the first pass of ECAP at 473 K are measured and compared with simulated textures obtained by the standard VPSC approach and the combined approach. In comparison with the standard VPSC approach, the combined approach gives better texture predictions for the two cases: The missing components at low to intermediate rolling reductions in the standard VPSC approach are reproduced; at high rolling reductions and after ECAP, the dominating fibers are also essentially smoothened in the combined approach, in better agreements with the experimental textures. [ABSTRACT FROM AUTHOR]

Temperature-dependent single-crystal elastic stiffness constants and the associated polycrystalline aggregate properties of fcc-based metal nitrides (MNs; M = Ti, Al, Zr, and Hf) have been investigated using a quasistatic approach via first-principles calculations. It is confirmed that the four studied nitrides are brittle materials and mechanically stable, agreeing with experimental results. Among these compounds, TiN and AlN possess the highest strength and the highest hardness, respectively. The cross-slip and the resistance to microcracks are analyzed based on the elastic anisotropy ratio. Additionally, it is found that the decreasing trend of C11 with respect to temperature is larger than that of C12 or C44. With increasing temperature, the resistance of shear deformation, stiffness, hardness, and strength of these four nitrides decrease. The computed properties of MNs agree well with the experimental data available in the literature. [ABSTRACT FROM AUTHOR]

Copper-diamond composites are increasingly being considered for thermal management applications because of their attractive combination of properties, such as high thermal conductivity ( λ) and low coefficient of thermal expansion (CTE). In this research, thermal properties of Cu-diamond composites with two different types of interfacial carbides (CrC and SiC) were studied. The interface thermal conductance ( h) was calculated with Maxwell mean-field and differential effective medium schemes, wherein experimentally measured λ was entered as an input parameter. The λ and h of both the Cu-CrC-diamond and Cu-SiC-diamond composites are higher than those reported in previous studies for Cu-diamond composites with no interfacial carbides. The value of h is intimately related to the morphology and thickness of the interface carbide layer, with the highest h being associated with a thin and continuous interface carbide layer. A lower h resulting from a thicker CrC layer can provide an alternate explanation for a previously reported trend in λ of Cu-CrC-diamond composites with different Cr-contents. The experimentally measured CTE was compared with the Turner and Kerner model predictions. The CTE of both the Cu-CrC-diamond and Cu-SiC-diamond composites is lower and better matches the model predictions than the previously reported CTE of Cu-diamond composite with no interfacial carbides. The CTE of Cu-CrC-diamond composites agrees better with the Kerner model than the Turner model, which suggests that deformation during temperature excursions involves shear. [ABSTRACT FROM AUTHOR]

A fiber placement device is described and methodology is given for preparing two-dimensional (2-D) and three-dimensional (3-D) combinatorial microcomposites. Although 2-D microcomposites with uniform fiber spacing have been prepared previously, the preparation of uniformly spaced 3-D microcomposites with 6–20 μm diameter fibers is new. The preparation of these combinatorial specimens was motivated by research results from reference [Li et al. (1995) Compos Sci Technol 54:251]. These results showed that the mean fragment length of the broken fibers in an array of fibers of the shear-lag models increases as the inter-fiber separation decreases. It was noted that shear-lag theory predicts the opposite effect. Therefore, specimens of this type are needed to unambiguously verify this trend. In addition, data from this new technology should delineate the factors that influence critical flaw nucleation in unidirectional laminate composites. [ABSTRACT FROM AUTHOR]

High-speed rolling of AZ31B was carried out under various preheating temperatures from RT to 350 °C. The evolution of texture, grain sizes, and dislocation density distribution (Kernel average misorientation distributions) in the mid-thickness and surface layer were investigated. Computer simulations of deformation textures were also performed in order to understand deformation mechanisms. It is concluded that the temperature increase due to the plastic and frictional working during high-speed rolling makes the slip system more active and, hence, improves the ductility. The surface layer of the specimen has higher temperature and experiences severe shear stress; therefore the texture, microstructure, and dislocation density distribution are different from those of the mid-thickness of the specimen. Both mid-thickness and surface layer are dynamically recrystallized during the high-speed rolling. [ABSTRACT FROM AUTHOR]

A general procedure for texture simulation in multi-pass equal channel angular pressing (ECAP) with capability of applying different processing routes is proposed. The program inputs are the initial texture and the loading condition and the output is texture after deformation. Deformation texture in ECAP of aluminum rod was predicted based on simple shear model for deformation and Visco plastic self consistent model for texture simulation. The simulation was done for two consecutive passes of ECAP and the results were compared with experimental texture measurements. The initial texture of the sample before ECAP was found to play a key role in formation of the final texture and a good agreement between the simulated and the experimental texture was obtained. [ABSTRACT FROM AUTHOR]

Microstructure and fracture behavior of brazed joint between commercially pure titanium and low carbon steel using silver (Ag–34Cu–2Ti) and copper (Cu–12Mn–2Ni ) based alloys have been characterized to determine the effect of brazing parameters and chemical composition on the strength of brazed joints. It is found that the shear strength of brazed joints strongly depends on the lap width. Furthermore, the fracture path and the value of shear strength significantly changed with the type of filler alloy. The two filler metals showed metallurgical interaction with steel and titanium forming different kinds of intermetallic compounds such as CuTi, Cu2Ti, and FeTi with silver based filler and Ti2Cu, FeTi and TiCuFe with copper based filler. [ABSTRACT FROM AUTHOR]

The shear strength of pure nickel (Ni), and its alloy, Ni–60Co (by wt%), has been determined during one-dimensional shock loading in the impact stress range 0–10 GPa. The influence of the reduced stacking fault energy (SFE) for the Ni–60Co has been investigated. The shear strength (τ) and the lateral stress (σ y ) both increase with the impact stress for each material. The shear stress has been found to be higher in the nickel than in the alloy. The progressive decrease of the lateral stress behind the shock front indicates an increase of the shear strength. A more complex mechanism of deformation has been found for the alloy since twin formation has been observed in the microstructure, while none has been seen in nickel. It is thought that mechanical twinning plays a predominant role in the deformation mechanism of the alloy resulting in the reduction of the material strength. [ABSTRACT FROM AUTHOR]

Single crystals of nominally pure KCI and KCI doped with Mg2+, Ca2+, Sr2+ or Ba2+ were deformed by compression at 77-254 K; during the tests strain-rate cycling was conducted in association with ultrasonic oscillation. The data were analyzed in terms of strain-rate sensitivity ((Δτ'/Δln ε)) versus stress decrement (Δτ). The curve for KCI doped with the divalent impurities has two bending points and two plateau regions. It is proposed that the variation of strain-rate sensitivity at the second plateau place on the curve with shear strain (Δ(Δτ'/Δln ε)/Δε) is due to a change in forest dislocation density with shear strain. The forest dislocation density for the specimens seemed to increase by the divalent additions in the compression test on account of the jogs on the screw dislocations. It depended on the concentration of impurities and also on the size of impurity in the specimens at a given temperature. Unfortunately, it was not possible to determine whether a change in the size of impurity influences mobile dislocation density, ρ, from the values of Δρ/Δτ' for KCl doped with Ca2+ Sr2+ or Ba2+. [ABSTRACT FROM AUTHOR]

The accommodation of severe plastic deformation in impact crater formation, ballistic rod flow and penetration in thick targets, shaped charge formation, and a variety of friction-stir welding and processing is shown to occur by microstructure refinement, particularly dynamic recrystallization in the development of localized or overlapping adiabatic shear bands. Optical metallography and transmission electron microscopy observations of solid-state flow in adiabatic shear zones are compared to illustrate these mechanisms which can often involve intermixed microstructural regimes composed of recovery, recrystallization, and grain growth phenomena. [ABSTRACT FROM AUTHOR]

Single crystals of a Cu-Fe alloy, which contained spherical γ-Fe particles, were compressed up to shear strain of 0.17 in liquid nitrogen bath. In the process of straining the structural (optical and TEM) observations in as-deformed and post-deformation annealed samples were provided. The substructure of deformed samples was characterized by slightly developed cell structure and lack of distinct layer-like arrangements of dislocations. Three kinds of particles were found: coherent and semi-coherent f.c.c. γ-Fe and martensiticly transformed b.c.c. α-Fe. The critical diameter for coherency loss was found to be 58 nm at the initial stage of deformation decreasing with strain to 50 nm. These values coincided with the theoretical estimations. It was suggested that relaxation of coherency strains around γ-Fe particles by the generation of interface dislocations might occur prior to the martensitic transformation. This assumption might explain the particle size dependency of martensitic transformation. [ABSTRACT FROM AUTHOR]

Epoxy resins with various molecular weights between cross-linkings were prepared. In order to examine the strain rate and temperature dependence of the shear yield strength and the shear strength, test specimens were subjected to shear deformation at various strain rates and temperatures. The shear yield strength and the shear strength increased almost linearly as the logarithm of the strain rate increased. The strain rate-temperature superposition held for these shear properties. In particular, an experimental equation of the strain rate-temperature superposition for the shear yield strength was found. The shift factor to obtain a master curve was given with the temperature dependence of an Arrhenius type. Furthermore, the strain rate-temperature-molecular weight between cross-linkings superposition held for the shear properties. [ABSTRACT FROM AUTHOR]