In-plane Shear Research Articles

On the experimental determination and prediction of damage evolution in composites via cyclic testing

This study introduces a novel approach to obtaining and predicting damage evolution laws using quasi-static cyclic testing within the framework of continuum damage mechanics. To achieve this, a comprehensive set of characterization and parameter identification tests was performed. Carbon-epoxy specimens were manufactured using the filament-winding technique, and these laminates were tested using a universal testing machine. Digital image correlation was employed in all experiments to capture strain fields, and an alternative method utilizing the combined loading compression device is presented to obtain mechanical properties. Once the material was characterized, cyclic tests were conducted, including [Formula: see text], [Formula: see text], and [Formula: see text] tensile tests, and shear v-notch tests. These aim to determine damage evolution laws for both conditions, pure and coupled stress states. From these tests, values for damage onset and threshold were obtained and used to define four new parameters. These parameters permit the estimation of degradation relationships for any arbitrary orientation without requiring additional tests. This approach was tested as the proof-of-concept within the positive range of transverse tension and in-plane shear stress domain. The obtained results are promising, justifying its extension to other failure mechanisms. While acknowledging its limitations, this new approach holds potential for implementation in the analysis of progressive failure in fiber-reinforced composite materials, possibly in conjunction with established failure criteria and computational tools, mainly in the finite element method domain.

Microstructure and texture evolution in AZX311 Mg alloy during in-plane shear deformation

The current study examined the deformation mechanisms, microstructure, and texture evolution in AZX311 Mg alloy sheets subjected to in-plane shear (IPS) deformation. Different levels of shear strains, with values 0.05, 0.10, and 0.15, were applied along the rolling direction (RD) using a specialized in-plane shear testing jig. The strain measurement for the applied shear deformation was conducted utilizing the digital image correlation (DIC) technique. The strain distribution was found to be nearly homogeneous over sufficiently large areas, thereby allowing the microstructural measurements to yield relevant statistical data. A thorough microstructural examination across the thickness using electron back-scattered diffraction (EBSD) revealed that the application of IPS strain led to the formation of a significant number of tensile twins (TTWs) in the sheet. This was evidenced by the emergence of two satellite peaks at the periphery of the pole figures. As the shear strain increased, the proportion of TTWs in the material also increased, encompassing the entire parent grain and leading to the formation of what has been termed as “all-twinned microstructure”. The microstructural and texture investigation after IPS deformation revealed that TTWs were the dominant deformation mechanism that defined the microstructure and texture under IPS deformation, while dislocation slip activity was dominated by prismatic slip, as evidenced by the resolved shear stress analysis in this study. Consequently, this research highlights the effect of IPS deformation on the microstructure and texture evolution throughout the thickness of an Mg alloy sheet and elucidates the underlying mechanisms.

Arching effect in slopes under excavation: Classification and features

Classifying excavation-induced slopes considering the arching effect and understating the features are crucial for determining the appropriate designs for excavation, assessing the long-term behaviors of excavations, and identifying potential failure modes. The objective of this study is to establish a classification system for excavation-induced slopes and to identify the features and applications of each slope. A series of physical model tests were carried out to investigate the deformation and failure behaviors of slope under different conditions. Assisted with the monitoring of earth pressure cells, digital and high-speed cameras, the deformation and failure characteristics were analyzed through particle image velocimetry (PIV) analysis. The results show that the slope models can be separated into three types: “shear plane arching” slope; “partial arching” slope; and approaching “full arching” slope. During the prefailure process, unyield zone ratio decreases from “shear plane arching” slope to “particle arching” slope to approaching “full arching” slope, while the yield zone ratio and interaction zone ratio increase. In the postfailure, the “full arching” slope can create higher initial kinetic energy. The classification and features of the excavation-induced slopes helps to supply engineers with the information for guiding the operation at sites.

Nonuniformity in stress transfer across FRP width of FRP-concrete interface

The nonuniformity of stress and strain analysis is an important consideration that describes the bond behavior between concrete and externally bonded fiber reinforced polymer (FRP) laminates. The interfacial stress transfer between FRP and concrete generates a longitudinal strain gradient in the longitudinal (or FRP fiber) direction. Most of the available studies in this area have focused on nonuniformity in the longitudinal direction. In this paper, the nonuniformity in the FRP width direction is investigated by studying the strain distribution using digital image correlation (DIC) full-field optical techniques. In the direction along the FRP width, there is an area in the middle that has consistent strain and stress, while the edge regions have strain and stress gradients. During the complete debonding process, the width of the central area is found to be insignificantly affected by the concrete strength but significantly affected by the FRP stiffness. The fracture characteristics below the central region are purely Mode II fracture. However, the complex curved cracks and high in-plane shear strains at the interface near the FRP edge regions show a mixed mode with Modes II and III. This boundary effect results in a significant difference in the bond–slip characteristics of FRP along the width direction. The maximum bond stress of the central region is higher than that of the edge region. However, for FRP with higher stiffness, the inhomogeneity of the stress distribution is weakened. Moreover, it is reasonable to find that calculating the sum of the bearing capacity of the single FRP strips along the width direction is close to the experimental bond strength. Based on the research findings in this study, it is qualitatively recommended that the width factor model in calculating FRP-concrete bond strength should include the significant effect of FRP stiffness.

Coupled effects of temperature and suction on the anisotropic elastic shear moduli of unsaturated soil

Elastic shear moduli of soil at various temperatures and suctions are important for analysing the serviceability limit state of energy piles and many other structures. Up to now, however, the coupled effects of temperature and suction on elastic shear modulus and the stiffness anisotropy, have not been well understood. This experimental study investigated the anisotropic elastic shear modulus of a compacted lateritic clay. A temperature and suction-controlled triaxial apparatus equipped with bender element probes and local strain measurements was used. Soil suctions from 0 to 300 kPa, and a temperature range of 5–40 °C were applied. The results at saturated and unsaturated conditions consistently reveal that the shear modulus is smaller after heating at a given stress and suction. Several mechanisms may contribute to this thermal-induced reduction in shear modulus, such as the heating-induced reduction of interparticle force and air–water surface tension. Moreover, the reduction in shear modulus upon heating depends on the shear plane and the degree of anisotropy changes.

Impact Response Features and Penetration Mechanism of UHMWPE Subjected to Handgun Bullet.

Ensuring military and police personnel protection is vital for urban security. However, the impact response mechanism of the UHMWPE laminate used in ballistic helmets and vests remains unclear, making it hard to effectively protect the head, chest, and abdomen. This study utilized 3D-DIC technology to analyze UHMWPE laminate's response to 9 mm lead-core pistol bullets traveling at 334.93 m/s. Damage mode and response characteristics were revealed, and an effective numerical calculation method was established that could reveal the energy conversion process. The bullet penetrated by 1.03 mm, causing noticeable fiber traction, resulting in cross-shaped failure due to fiber compression and aggregation. Bulge transitioned from circular to square, initially increasing rapidly, then slowing. Maximum in-plane shear strain occurred at ±45°, with values of 0.0904 and -0.0928. Model accuracy was confirmed by comparing strain distributions. The investigation focused on bullet-laminate interaction and energy conversion. Bullet's kinetic energy is converted into laminate's kinetic and internal energy, with the majority of erosion energy occurring in the first four equivalent sublaminates and the primary energy change in the system occurring at 75 μs in the fourth equivalent sublayer. The results show the damage mode and energy conversion of the laminate, providing theoretical support for understanding the impact response mechanism and improving the efficiency of protective energy absorption.

Cost-effective topology optimization of masonry structure reinforcements by a linear static analysis-based GA framework

The paper presents a novel optimization framework aimed at the minimization of seismic retrofitting-related costs for existing unreinforced masonry building structures. The framework provides topology optimization of reinforcements (reinforced plasters) to implement in masonry walls for the accomplishment of seismic safety checks under the reference seismic load combinations. Optimization is carried out by a genetic algorithm (GA) developed in MATLAB®, which controls a 3D finite element equivalent frame model of the masonry structure developed in OpenSees. The GA routine iterates the reinforcement configurations employing specific genetic operators. The feasibility of each candidate retrofitting solution is assessed by performing in-plane shear and flexural safety checks of masonry walls. The framework is finally tested with a case study masonry structure supposed to be made of average-quality or poor-quality masonry. Results will show that the proposed framework can effectively provide the minimization of seismic retrofitting costs for existing masonry structures, giving as output the optimal configuration of the reinforcements within the structural layout.

Exploring in-plane shear characteristics of multilayer biaxial weft knitted fabrics through a micro-scale virtual fiber modeling

The multilayer biaxial weft knitted (MBWK) fabrics and their composites have been widely applied in fields of complex structural products due to their flexible curved deformability. The existence of stitch in MBWK complicates the deformation behavior under the in-plane shear loading. However, it has not been well explored and understood. In this study, a numerical micro-scale virtual fiber modeling was built to investigate the in-plane shear performance of MBWK by considering the micro geometric features and fiber property that are difficult to be characterized solely by experiment. The strain conditions of the stitch that determine the fabric shear behavior are discussed. The deformation behavior leads to local deformation and morphological locking of the stitch. In the early stage of the shearing, the deformability of stitch provides enough space to accommodate the rearrangement of axial yarns. In the shear locking stage, the restriction of stitch and compression within axial yarns at high shear angles restricts the axial yarns from movement in the loading direction. When the theoretical shear angle is 20°, the shear angle located in different shear regions varies. The maximum shear angle near the loading area is 19.1°, while the minimum shear angle near the fixed area is approximately 17°. The results illustrate the deformation mechanism of MBWK under in-plane shearing and provide an excellent guidance for the design of large deformation fabrics, especially for curved surfaces, thus realize the effective utilization of fabrics in engineering applications.

Stress, damage, and fatigue performance analysis of CFRP/Al double-sided countersunk riveted joints with variable rivet-hole clearance

The CFRP/Al countersunk rivet joints are one of the most fatigued dangerous points of the aircraft fuselage. To deeply investigate the failure mechanisms of the riveted joint structures, this paper utilizes electromagnetic riveting technology to prepare single-lap joint specimens and investigates the quasi-static tensile and fatigue failure behaviours of the joints under different rivet-hole clearances and stress levels. In addition, to assist this investigation, a three-dimensional finite element model, combining riveting and fatigue loading, is developed. This model takes into account the strain rate effects during riveting process and progressive failure behavior of various typical damage modes in CFRP laminates. The results indicate that Aluminum alloy sheets fracture dominates the fatigue failure of the joints. Increasing the clearance can reduce the stress amplitude on the shear plane and further enhance the fatigue life of the joints. Furthermore, all additional CFRP damage during the loading process is the growth of the initial riveting damage, and the damage-induced fibre bearing capacity decrease is considered the reason for the increase in stress amplitude of the Al sheet. Last, excessive clearance enlargement does not appreciably diminish the initial riveting damage, instead, it could result in a joint strength reduction.

Investigation on mechanical behaviors and energy characteristics of deep-buried marble in a hydraulic tunnel in Southwest China

Shear behavior of rock is of great significance to the stability of deep-buried rock in transportation geotechnical engineering. A series of direct shear tests are carried out on deep-buried marble with different size and shape to focused on the mechanical properties and size shape effects of deeply buried marble, which have been less studied previously. The results show that the size and shape of the specimen have a relatively small impact on the trend of shear stress-shear displacement curve. The failure morphology at the front and rear surfaces shows a significant normal stress effect. Some properties of specimens with different sizes and shapes increase with increasing normal stress, but the dilation angle generally decreases with the increasing normal stress. With the increase of the shear plane size of intact specimen, the cohesion decreases gradually while the internal friction angle increases steadily. The difference value in peak strain between axial compression and direct shear tests is relatively small while it is huge for the peak compression and peak shear strength. The results in this study are beneficial for further understanding the shear mechanics, energy evolution process and size effects of deep-buried rock in transportation geotechnical engineering.

High Temperature Experiments and Properties of Carbon Polyimide Composites

The interlayer shear tests of AC741/M55JB carbon fiber reinforced composite at room temperature, 400℃, 600℃ and 800℃ were carried out.The longitudinal and transverse shear tests of AC741/CCF800 carbon fiber reinforced composite were carried out at room temperature, 400℃, 600℃ and 800℃ dry conditions, as well as the experiments to calculate material property parameters. The results showed that the main failure mode of the sample in the interlayer shear test was stratified damage, and the fracture of the upper surface material was not obvious.This is due to the different types of tests, the interlayer shear pattern is short and small, and it is not easy to occur the fracture damage of the material without stratification.In addition, with the increase of temperature, the interlaminar shear strength also decreased significantly.In crossbar shear test, the maximum in-plane shear stress, maximum in-plane shear strength and in-plane shear modulus of the material gradually decrease with the increase of temperature, thus changing the bearing property of the material.

Effect of Strain Hardening on Burr Control in Drilling of Austenitic Stainless Steel

Austenitic stainless steel has been widely used in various industries, such as aerospace, medical, and hydrogen energy, due to its high strength over a wide range of temperatures, corrosion resistance, and biocompatibility. However, stainless steel is a difficult-to-cut metal because its ductility and low thermal conductivity induce a strain hardening with significant plastic deformation at high temperatures. Burr formed at the back side of a plate is a critical issue which deteriorates the surface quality, especially in drilling. Burr removal operation, therefore, should be done in the machine shop. This study discusses the effect of strain hardening of austenitic stainless steel, SUS 316L, on burr formation. Hardness and cutting tests were conducted to compare the strain hardening effect for three types of workpieces: as-received, pre-machined, and tensile treated specimens. In the employed specimens, the tensile treated specimen is harder than the as-received specimen. Those specimens have uniform hardness in the depth direction from surfaces. Pre-machined specimen, in which the back side of the plate was finished by face milling, has a distribution of hardness in the depth direction from a surface. The highest hardness appears in the subsurface of the pre-machined specimen. The cutting forces in the steady processes, in which the entire edges remove material, were nearly the same as the tested specimens each other. However, remarkable differences were confirmed in the chip thickness and burr formation. The higher strain hardening of the tensile treated specimen is effective to suppress burr formation. The cutting characteristics are then identified to associate burr control with the shear plane model of orthogonal cutting using an energy-based force model. The shear stresses, shear angles, and friction angles of the tensile treated and as-received specimens are compared to discuss the effect of strain hardening on reduction of burr formation.

Effect of the loading-rate and stress state on the constitutive modelling and fracture of 2205 Duplex stainless steel

Shear cutting is a high-speed forming process where material separation is involved. The nature of the process leads to high strain rates and temperatures on the sheared zone of the material subjected to the operation. In this work, the mechanical behavior in terms of flow stress, plastic deformation and fracture of a 2205 Duplex stainless steel sheet is determined. Uniaxial tension, uniaxial compression, stack compression, plane strain tension and simple shear tests at different angles with respect to the rolling direction of the metal sheet are performed to determine the anisotropic behavior of the material. Strain rate and temperature dependence of the flow stress and the plastic behavior of the material is determined through notched tensile tests performed under various temperatures (20°C, 100°C, 300°C and 500°C) and strain rates (0.001 s-1, 10 s-1 and >100 s-1). Finally, fracture behavior under various stress states is determined through notched tensile, central hole, in-plane shear and plane strain tests. The temperature and strain rate dependence of the fracture behavior is determined through notched tensile, in-plane shear and plane strain tests performed under various temperatures (20°C, 100°C, 300°C and 500°C) and strain rates (0.001 s-1, 10 s-1 and >100 s-1). The anisotropic behavior and work hardening of the material are modelled by the Hill48 yield function and Swift-Hockett-Sherby hardening law, respectively. Among the two ductile fracture models tested, Hosford-Coulomb model showed the best agreement and is therefore used to account for the temperature and strain rate effects on the fracture behavior. By combining these three models, an accurate reproduction of the mechanical behavior of the 2205 Duplex stainless steel sheet is achieved.

Study on the effect of high temperature on the mechanical properties of composites plates containing initial defects

In this study, against the background of the high temperature environment faced by hypersonic vehicles, an in-depth study is carried out to investigate the influence of temperature on the mechanical properties of reinforced wall plates of composites containing initial defects. First, the in-plane shear mechanical property data and failure morphology of two groups of specimens of T1100/5405 composites at different test temperatures (25°C, 150°C) were obtained through experimental tests. The tests show that high temperature accelerates the damage failure process of the wall plate structure, the shear capacity of the wall plate is weakened, and the ultimate load decreases by 26.06%. Secondly, a numerical model based on the CZM and the CDM of the composite is established, and the accuracy of the model is verified by combining with the test results. The work carried out in this paper has certain engineering application value for the design of composite structures for hypersonic vehicles.

Kirigami beyond tension: Expanding Kirigami's versatility via shear actuation

The potential of Kirigami-based metamaterials as versatile platforms in applications where shape-morphability is desired is presently well established. Interestingly, in-plane loading under simple tension has been the predominant actuation-of-choice, with other fundamental loadings (e.g., shear, torsion) being largely overlooked. In this work, we explore the instability landscape of a simple Kirigami motif under in-plane shear loading and demonstrate how the incorporation of shear actuation effectively augments both the design and output space of Kirigami-based metamaterials. The nonlinear response of Kirigami under shear is first elucidated parametrically via nonlinear Finite Element Analysis on a subset of geometrically asymmetric motifs. The interplay between cut layout and the bidirectional nature of in-plane shear enables a variegated bifurcation landscape that includes unusual inversions and sharp kinks in the bifurcation curves. The numerical analysis is complemented with experimental validation of the out-of-plane bifurcation curves of several cases of interest by means of shadow moiré and laser displacement sensing. Together with the experimental validation, a proof-of-concept demonstration of the applicability of Kirigami-shear metamaterials as multistate electro-mechanical switches is presented. Overall, our findings add a new dimension to an already rich design space, thus opening a vista of opportunities for multimodal programmable structures, particularly appealing in sensing and actuation applications.

Stability and Elasticity of Ultrathin Sphere-Patterned Block Copolymer Films.

Sphere-patterned ultrathin block copolymer films are potentially interesting for a variety of applications in nanotechnology. We use self-consistent field theory to investigate the elastic response of sphere monolayer films with respect to in-plane shear, in-plane extension, compression deformations, and bending. The relations between the in-plane elastic moduli are roughly compatible with the expectations for two-dimensional elastic systems with hexagonal symmetry, with one notable exception: The pure shear and the simple shear moduli differ from each other by roughly 20%. Even more importantly, the bending constants are found to be negative, indicating that free-standing block copolymer membranes made of only a sphere monolayer are inherently unstable above the glass transition. Our results are discussed in view of the experimental findings.

Validated Finite-Element Model for Predicting Asphalt Concrete Overlay Reflective Cracking Potential

The reflective cracking potential of overlay systems is often studied through large-scale testing, which is time-consuming and expensive. Therefore, a generalized 3D finite-element model was developed to simulate a large-scale test setup to predict the reflective cracking potential. Crack propagation was modeled, and fracture parameters, such as stress intensity factor (SIF) and J-integral, were obtained. Mode I cracking dominated the model’s crack propagation, while in-plane shear cracking was insignificant. The model was validated with large-scale testing results; the average Mode I SIF was found to be a valid measure to assess the overlays’ reflective cracking potential. The model could be used qualitatively to compare different overlay configurations. A database of 128 cases was generated to compute fracture parameters for extreme scenarios or a combination of inputs. A data-driven surrogate model that predicts reflective cracking potential was developed to allow easy application by agencies. Shapley Additive Explanations (SHAP) analysis confirmed the model’s robustness. The surrogate model may be used by engineers to select asphalt concrete mixtures and design overlay thicknesses to control reflective cracking potential.

Experimental investigation of size effect on unreinforced concrete brick masonry walls under in-plane shear loading

The size effect is one of the primary structural characteristics exhibited in reinforced concrete (RC) members in shear. Even though numerous studies have been conducted on masonry walls under shear, very few studies have been conducted that definitively answer whether a size effect exists for masonry walls. Diagonal compression tests on two groups of masonry walls with different dimensions were conducted to investigate the size effect on concrete brick masonry walls. A total of sixty masonry wall panels were tested. Five bed-joint mortar mix properties were used for each specimen. Test results showed that four failure modes were observed: diagonal tension failure, combined failure, sliding failure, and toe-crushing failure. In particular, the diagonal tension strength was significantly related to the specimen size. The larger specimen size led to a lower shear strength. Also, the shear modulus was highly dependent on the specimen size. Through experimentation, this study demonstrated that masonry walls exhibit a size effect. Moreover, the size effect is valid only in cases of diagonal tension failure. Based on the test results, this study revealed a correlation between diagonal tension strength and wall size. Lastly, the adequacy of the predictions was compared to the existing masonry codes.

Material characteristic-controlled particle segregation in rock-ice avalanche

Rock-ice avalanches exhibit significant particle segregation driven by density and friction differences between ice and rock. This study meticulously uncovers intricate segregation dynamics in rock-ice avalanches, focusing on density variations, friction disparities, and ice volume fractions through physical flume experiments and numerical simulations. Results reveal clear patterns: ice particles cluster at front regions in flow, while rocks move to the rear. Ice occupies upper flow-depth areas, while rocks settle lower. In density-controlled segregation, low-density ice segregates upward and forward due to diminished inertia, whereas in friction-controlled scenarios, low-friction ice displays heightened flowability, causing forward and downward segregation. Density-controlled and friction-controlled segregation both result in forward segregation in the flow direction, exhibiting competitive dynamics in flow-depth. Lower ice volume fractions increase the relative slip of ice particles along shear planes, and decrease the relative slip of high-density rock particles in the flow-depth direction, accentuating forward segregation and reducing it in flow-depth.

Buckling optimization of variable stiffness helicoidal composite laminates based on semi-analytical method

Variable stiffness laminates and helicoidal composites have gained significant attention in recent years. This paper introduces a novel structure called variable stiffness helicoidal composite laminates, which combines these two materials. The fibers in each layer are arranged in curved paths, and all the layers are stacked in a helicoidal pattern. To ensure uniform thickness throughout the laminate, an equidistant placement method is proposed for designing the curvilinear fibers. By establishing the energy equation and fitting the displacements with Legendre polynomials, a semi-analytical method is proposed to determine the critical buckling load. An integrated design framework is developed to obtain the optimal design. The optimized models show more than 10% enhancement in the critical buckling load compared to the quasi-isotropic laminate under uniaxial compression and in-plane shear.