Shear Response Research Articles

A unified method to generate representative volume elements with tailored random fibre arrangements to estimate the shear and transverse behaviours of unidirectional continuous fibres composite plies

Axial compressible strength is a key design parameter of CFRP laminate structures, especially for Aerospace where maximum flexure on wings is driven by the global margin of safety on compressive loads. One of its main limiting contributors is the non-linear shear behaviour of the unidirectional ply. This shear response can be predicted by using generated (quasi-)random microstructures set within representative volume elements (RVE). Different microstructures with or without clusters of fibres (resulting from manufacturing processes) are necessary to quantify the mechanical variability. The variability of the microstructures is characterised by the variation of the arrangement, the volume fraction and the misalignment of the fibres. This leads to significant variations in the mechanical performance, in particular for the shear behaviour. In this study, we propose a unified algorithm that makes it possible to generate all the different positions of fibres in microstructures with very high fibre volume fractions. The microstructural parameters responsible for variations in mechanical behaviour are identified to establish a correlation between fibre distribution and the mechanical response. Finally, a composite cross-section is analysed to estimate the local non-linear shear behaviour as well as the compressive strength as an example to illustrate the benefit of complex microstructures modelling.

The Shear Performance of an Aircraft off Pin Made of Quartz Fiber Reinforced Phenolics: The Effect of the Fiber Distribution Property

Emergency breakaway pins (EBPs) have been widely used in aircraft, especially in the suspension connection between the engine device and the airfoil. Currently, the existing EBPs, which are made of metal materials, barely satisfy the lightweight requirement of the airplane industry. Thus, the construction of a novel EBP with quartz fiber reinforced phenolics is proposed in this study, and the shear response is examined experimentally using a double-sided shear test. The effect of the fiber distribution characteristic on the shear strength is then assessed quantitatively. The failure patterns, including the damage morphology of the two types of samples were then reconstructed using scanning electron microscopy (SEM). Experimental results showed that the breakaway composite pin fabricated by the laminated composite had a superior shear response than its counterpart with randomly distributed fibers for its uniaxially distributed fiber yarns provided a longer put-out damage trace that contributed to a higher shear-loading bearing capacity for the entire composite EBP. In specific, the average values of the shear strength and the shear stiffness for the former samples were higher by 61% and 22%, respectively, than that for the latter samples. Additionally, the composite EBP also has an excellent combination of lightweight advantage and stronger shear-bearing capacity over competing pins, providing novel insight for more secure designs for civil and military aviation.

Validation of a Repurposed pH Monitoring Capsule for Cecal Applications Using Novel Synthetic Cecal Contents

Abstract This study presents a novel approach to monitoring pH changes in the cecum, a critical step toward understanding the dynamic interactions between the gut microbiota and probiotics. By repurposing the Bravo® capsule, originally designed for esophageal pH monitoring, we demonstrate its potential for accurate, continuous, and nonobstructive pH detection within a simulated cecal environment. To facilitate this investigation, we introduce the first synthetic cecal content (SCC) formulation. Our formulation closely mimics the mechanical properties of porcine cecal contents, particularly in terms of viscosity and shear response. This SCC recipe addresses a significant gap in the availability of simulated biological fluids for in vitro medical device testing. Rheometric analyses confirm the SCC's consistency with biological cecal contents, providing a cost-effective and efficient platform for preliminary device evaluations. Experimental results show that the Bravo® capsule can accurately detect pH changes within the SCC, closely matching readings from a handheld pH probe. The successful validation of the Bravo® capsule's performance in a simulated cecal environment, along with the development of a reliable SCC formulation, paves the way for future in vivo studies in porcine models. This research represents a significant advancement in the field of gut microbiome monitoring and holds promise for the development of targeted, microbiome-based therapeutics. By enabling real-tim/e, in situ analysis of the cecal microbiota's response to various interventions, this approach has the potential to revolutionize our understanding of the complex interplay between probiotics, diet, and gut health.

Multiscale evaluation of sand-geomaterial interface shear response in terms of material geometry effects

This study evaluates the effects of particle and surface geometric features on the interface shear behavior of sand-geomaterial. Particle shape and size were adjusted for the sand, and surface roughness form and height were set for the geomaterial part. 3D printing technology was used to produce geomaterials in the desired form. A custom-made transparent interface shear box was developed to perform digital image processing. For macroscale response, peak and residual strengths and dilation angle were measured. Sliding percentage and shear band thickness were determined from digital image correlation analyses for the mesoscale response. The experimental results showed that the macroscale response parameters increased as the overall regularity of the sand particles decreased. The increase in mean particle size and roughness height led to an increase in macroscale parameters. Digital image correlation analyses showed that the sliding percentage had an inverse correlation with the shear band thickness in terms of the particle shape and the roughness height effects. The roughness form controlled the trend of mean particle size effects on the sliding percentage. Overall, the mesoscale parameters revealed the traces of interlocking response, particle kinematics, and the failure mechanism in the interface region. Thus, a bridge was established between meso- and macro-scale responses.

Role of particle shape in sheared granular media: Roundness and elongation

Particle shape is an intrinsic characteristic of soil particles that significantly influences mechanical responses. In this investigation, a meticulously calibrated and validated two-dimensional discrete element method (DEM) model of a biaxial shearing test was employed to simulate the shearing response of forty distinct particle shapes. The systematic evolution of particle roundness (R) and aspect ratio (AR) was achieved by utilizing idealized polygonal-shaped particles, aiming to comprehend their effects on the macro and micromechanical behaviors of granular materials. The results suggest that a reduction in R limits free rotations and enhances interlocking, thereby promoting relatively stable force transmission between particles and leading to a monotonic increase in shear strength. However, this effect diminishes as particles become more elongated. Conversely, a decrease in AR from 1.0 (increased elongation) constrains particle rotations, increases the coordination number, and enhances fabric anisotropy initially resulting in increased overall shear strength, reaching a maximum before exhibiting a decreasing trend, indicative of non-monotonic variation. For high elongations, notable fabric anisotropy impedes clear force transmission between particles thus facilitating interparticle sliding and overall strength diminishes. The extent to which AR impacts depends on the angularity feature of particles. Finally, a nonlinear equation has been proposed to predict the variation in critical state shear strength of granular samples, based on the R and AR values of the constituent particles.

Analysis of Wind Response of Braced and Unbraced Tall Building

As high-rise buildings become increasingly prevalent worldwide, their complex structural components and the need for high stability pose challenges for safety and design requirements. The present study investigates the influence of bracing systems and plan aspect ratios on the ability of tall buildings to withstand wind loads. The study aims to analyze the effects of these variables on the wind-induced responses of tall buildings and improve bracing system design for structures with high aspect ratios. Numerical simulations using finite element analysis software are conducted, creating various building models with different aspect ratios and bracing systems. The displacement, drift, base shear responses and time period of each model are examined to evaluate the effectiveness of different bracing systems. The results highlight the significant impact of aspect ratio on the response to wind loads, with larger aspect ratios experiencing greater motion and stress. However, well-designed bracing systems prove effective in reducing wind-induced motion and stress. The study provides insights on best bracing system for different aspect ratios, offering valuable insights for creating safer and more resilient high-rise buildings.

Performance-based seismic design of controlled rocking reinforced concrete frame with beam-end hinge

This study investigates the seismic performance of the Controlled Rocking Reinforced Concrete Frame with Beam-end Hinge (CR-RCFB) system. The novelty of our research lies in the development and validation of a finite element model that accurately predicts the dynamic response of CR-RCFB structures under various seismic conditions, specifically focusing on the innovative use of joint stiffness ratios and the integration of dampers. A finite element model was developed and validated through shaking table tests. The research examined the dynamic responses of the CR-RCFB under ten ground motion records, varying the node relative stiffness ratios. The interstory displacement amplification coefficient (α) was found to range between 1.08 and 1.20, while the earthquake-reduction coefficient (β) varied from 0.8 to 0.3 depending on the stiffness ratio. Results indicate that node stiffness ratios between 0.01 and 0.25 optimize performance, minimizing peak interstory displacement and base shear response. Additionally, integrating dampers increased the damping ratio from 14.48% to 30.51%, enhancing energy dissipation by shifting absorption from plastic deformation to damper yield. Pushover analysis was used to recalculate and validate the parameters α and β, demonstrating that the integration of dampers effectively controls displacement response. These findings suggest that the CR-RCFB system with integrated dampers offers enhanced seismic resilience by reducing displacement and base shear forces compared to traditional reinforced concrete frames.

Numerical Modeling of Distributed Macro-Synthetic Fiber and Deformed Bar Reinforcement to Resist Shear

Macro-synthetic fibers are increasingly used in concrete as secondary reinforcement to control temperature and shrinkage cracks, improving durability by limiting crack widths. However, their impact on the shear strength of structural elements remains underexplored, particularly when used in combination with traditional steel reinforcement. To address this knowledge gap, this study developed and calibrated a non-linear numerical model to simulate the shear response of macro-synthetic fiber-reinforced concrete (PFRC) elements, using finite element software VecTor2. The model was calibrated with experimental data from PFRC panels subjected to pure shear loading, incorporating a custom concrete tension-softening model to capture the contribution of fibers. Validation against a broad range of PFRC beam experiments from the literature demonstrated the model’s accuracy, achieving an average predicted-to-experimental shear strength ratio of 0.99 (COV = 5.5%). Additionally, the model successfully replicated key response characteristics such as deformation patterns, crack propagation, and residual strength. The proposed modeling approach provides valuable insights into the interaction between fiber volume and transverse reinforcement. It also serves as a powerful tool for future numerical studies, addressing the existing data gap on PFRC behavior and exploring the synergistic effects of macro-synthetic fibers and steel reinforcement on shear strength.

Analytical model for RC coupling beam considering axial restraint

A novel three-dimensional distributed plasticity model element is formulated and implemented into an open-source computational platform (OpenSees) to enhance nonlinear modeling approaches for lateral force resisting systems utilizing diagonally reinforced concrete coupling beams. The model incorporates a fiber-based concrete cross-section along with truss elements to represent the diagonal reinforcement and contact elements to model reinforcing bar slip at the beam-wall interface. The model is validated using test results from five different experiments that include variations in cross-section geometries, reinforcement configurations, and boundary conditions. Notably, two test specimens shared identical attributes except for their cross-sectional shapes (with and without a slab), whereas another pair were identical except for the degree of axial restraint provided. The final specimen utilized both longitudinal and diagonal reinforcement along the length of the beam. The model accurately predicted overall shear versus chord rotation responses with errors < 5 % and axial growth responses with errors < 30 %. The proposed model provides enhanced modeling options for nonlinear analysis by enabling sensitivity studies to address the potential impacts of coupling beam axial restraint on coupling beam and coupled wall behavior.

Parametric study for shear failure of bearing pads due to hurricane-induced wave loadings

The increasing frequency of extreme weather events, such as hurricanes and rising sea levels due to climate change, presents significant challenges to coastal infrastructure. With 42% of bridges in the United States exceeding 50 years of age, which surpasses their intended service life, there is a pressing need to assess their structural integrity, especially in coastal regions. This study focuses on evaluating the structural performance of bearing pads in coastal bridges under hurricane-induced wave loadings. Utilizing a combination of physics-based models (PBM), nonlinear modal time history analysis, and numerical validation, the research examines the hysteresis response of eight distinct bearing pad configurations. The findings indicate that reinforced circular bearing pads exhibit significantly greater shear displacements compared to plain elastomeric pads, underscoring the critical influence of shape factors on shear response. Fragility functions developed in the study illustrate the probability of shear failure, with reinforced circular pads showing a 28% higher likelihood of exceedance compared to rectangular plain pads. These results highlight the necessity for advanced design methodologies specifically for bearing pads to enhance the resilience of coastal infrastructure against severe hydrodynamic forces induced by hurricanes.

Exploring the micromechanical origin of shear response in granular materials induced by size non-uniformity

Exploring the micromechanical origin of shear response in granular materials induced by size non-uniformity

Modulating the behavior of ethyl cellulose-based oleogels: The impact food-grade amphiphilic small molecules on structural, mechanical, and rheological properties

This work evaluates the ability of various lipid-based amphiphilic small molecules (ASMs) to modulate the mechanical and rheological properties of oleogels principally structured by ethyl cellulose (EC). Six ASMs varying in the chemical structure of their polar headgroups were used to produce EC-ASM oleogels. Stearic acid (StAc), monoacylglycerol (MAG), sodium stearoyl lactylate (SSL), and citric acid esters of monoglycerides (CITREM) all provided a dramatic enhancement in gel strength, while lactic acid (LACTEM) and acetic acid (ACETEM) esters produced only a marginal increase. Those additives which crystallized above 20 °C displayed pronounced changes in their network organization and crystal morphology in the presence of EC. Differences in the solid/liquid phase change behavior were also observed in select samples using differential scanning calorimetry. Both the small and large amplitude oscillatory shear responses were dependent on the ASM which was dependent on the chemistry of the headgroup, crystal network organization, and ability to plasticize the polymer network. The extent of thixotropic recovery was largely dependent on the polarity of functional groups in the ASMs, but was also influenced by the formation of a secondary crystal network. In general, ASMs which formed larger, system-spanning crystal networks (MAG, StAc) produced more brittle gels, while the highly hydrophilic, charged headgroup of SSL promoted a homogeneous distribution of small crystals, resulting in a tougher material. In the absence of a crystal network, stronger polar species in the ASM headgroup produced higher gel strength and increased elasticity. Thus, both ASM chemical structure and crystallization properties strongly contribute to the functionality of the resulting combined oleogelator systems.

Flexural and interlaminar shear response of novel methylmethacrylate composites reinforced with high-performance fibres

This experimental work presents a comparative study on the mechanical behaviour of novel infusible methylmethacrylate matrix (Elium®) composites reinforced with different types of high-performance fibres. A vacuum-assisted resin infusion process was employed to fabricate the laminates using carbon, basalt, Kevlar®, and high molecular weight polyethene (UHMWPE) fibres. Flexural and interlaminar shear properties of the composites were evaluated. Test results revealed that carbon fibre composites had superior flexural strength, stiffness and interlaminar shear stress as compared to the other composites tested. Further, composites containing Kevlar and UHMWPE fibres demonstrated significantly higher flexural strains to failure. Post-testing, specimens were examined using scanning electron microscopy (SEM). Microscopy revealed possible interfacial interaction differences based on the reinforcement fibre type, which was further confirmed by an analytical approach for analysing the flexural behaviour of various types of composites. The sequence of damage progression in specimens was also analysed.

Off-axis mechanical behavior and dynamic characteristics of UHMWPE composite laminates

An understanding of the off-axis mechanical behavior and failure mechanisms of ultra-high molecular weight polyethylene (UHMWPE) cross-ply laminates subjected to quasi-static and dynamic loadings is developed, with focus on the influence of off-axis angle and strain rate. For off-axis tension, UHMWPE laminates exhibit polymer shear response characteristics. An orientation-hardening phenomenon is captured, as fiber rotation leads to local increment of load capacity along the loading orientation. The failure strength presents an evidentially descending trend with off-axis angle from 0° to 45°. A non-monotonic variation of strength with strain rate is further observed: increasing with strain rate up to 500 s−1 but decreasing above, which is attributed to failure mode switching from plastic failure to brittle failure. The Tsai-Wu failure criterion, on homogenized cross-ply laminae, is experimentally modified with rate dependence. Further investigation on detailed information of the unidirectional properties should be conducted with the backing-out scheme to establish unidirectional failure criterion.

Research on seismic suppression performance of vertical circulation stereo garage based on friction damper and steel pipe

AbstractThe conventional vertical circulation stereo garage is susceptible to deformation and instability when subjected to extreme seismic loads and complex working conditions. The present study introduces the combination arrangement of steel pipe and friction damper to optimize vertical circulation stereo garage while also investigating their seismic suppression performance under three representative seismic waves (EL‐CNENTRO, TH1TG025(TH), and RH1TG025(RH)). The results showed that the garage structure hasbetter seismic suppression performance when the combination of steel pipes and friction dampers is applied in Scheme 4 compared to relying solely on diagonal tie rod, steel pipe or friction damper. And Scheme 4 achieves inhibition rates of up to 61.27%, 22.12%, 56.07%, and 12.84% for overall maximum deformation response, maximum Y‐direction deformation response, vertex acceleration response, and bottom shear response, respectively. This enhancement significantly improves the garage's seismic stability, providing valuable theoretical references for advancing the development and market promotion of vertical circulation stereo garages.

On the dynamic shear failure of Ti-6Al-4V in different test specimen geometries

In this paper, the dynamic shear response and failure of Ti-6Al-4V using four different test specimen geometries, viz. Hat-Shaped Specimen (HSS), Flat Hat-Shaped Specimen (FHSS), Chip Hat-Shaped Specimen (CHSS) and Double Shear Specimen (DSS), are critically examined and compared. Through a combination of experiments (using the standard Split-Hopkinson Pressure Bar system), finite-element simulations and metallographic examinations of their fracture morphology, the dynamic shear characteristics (strain hardening, strain rate strengthening effect and failure strain) of Ti-6Al-4V obtained using the different specimen geometries are critically examined, compared and analyzed. It will be shown that differences in the stress/strain uniformity, the plastic deformation zone, and the stress state induced by the different specimen geometries lead to discrepancies in the measured shear response and failure that were observed. The shear stress–strain curve obtained using the DSS will be shown to be more precise than the other specimen geometries.

A generalized Bouc–Wen model for simulating the quasi-static and dynamic shear responses of helical wire rope isolators

This research investigates the mechanical behavior of a helical wire rope isolator deforming along its shear direction. In particular, we present the results of an extensive experimental campaign including both quasi-static and dynamic tests. The former provide hysteresis loops characterizing the device quasi-static behavior; the latter, performed by using an electro-mechanical shaker, furnish frequency response curves describing the dynamic behavior of a rigid block supported by the tested device. To simulate such a complex behavior, we adopt a generalized Bouc–Wen model and identify its parameters on the basis of the quasi-static test results. Subsequently, such a model is employed to reproduce the frequency response curves of the isolated rigid block. Since the results of the dynamic tests suggest the presence of rate-dependent hysteresis phenomena in the isolated system, the generalized Bouc–Wen model is enhanced by introducing a linear viscous component. Finally, to substantiate the model validation, the experimental results obtained by applying a series of white noise signals are compared with those obtained numerically to demonstrate the model capability of reproducing the device behavior in non-stationary response conditions.

Frictional strength of siliciclastic sediment mixtures in fault stability assessment

Frictional strength of fault zones is a key parameter for evaluation of fault stability and reactivation. We measure friction using the direct shear test (DST) for (i) sand-clay mixes mimicking fault gouges, and (ii) strength of fault zone interfaces. The sand-clay mixing ratio is linked to the established Shale Gouge Ratio (SGR) used in fault seal analysis, suggesting an approach for linking the measured frictional properties to the established subsurface fault characterization methods and risk assessment. We use powdered caprock material from the Draupne Formation mixed with sand to prepare the fault gouge and discuss application of results for fault zones on the Horda Platform, Norwegian North Sea.Shearing of fault gouge show a systematic decrease in residual friction coefficient with increasing clay content from 0.6 (φ = 31°) in pure sand (SGR 0%) to 0.4 (φ = 22°) for clay rich mixtures (SGR 100%). Interface testing mimicking fault gouge on sand surface is less systematic and shows residual friction coefficients ranging from 0.53 to 0.6 (φ = 28–31°) for SGR 0–50%. Detailed interpretation of the shear testing results shows changes in drainage properties, volumetric changes during shearing and shear responses to normal stresses indicating threshold values for sand versus clay dominated material behaviour. However, the results are non-conclusive on the question if a linear variation of friction with clay content or a threshold between sand dominated versus clay dominated friction provides the best approach for linking friction to fault clay content.

Seismic rehabilitation of RC frames with innovative precast U-shaped UHPC jackets: Experimental evaluation and computational simulation

The rehabilitation of post-earthquake reinforced concrete (RC) frames is crucial for both restoring structural integrity and enhancing seismic resilience against future seismic events. Ultra-high-performance concrete (UHPC) is distinguished by its exceptional strength, crack-control capabilities, ductility, and durability. Despite numerous studies on its use for structural retrofitting, its application in rehabilitating damaged RC frames remains limited. This study introduced a novel precast U-shaped UHPC jacket designed for the post-earthquake rehabilitation of RC frames. The jacketing method promotes composite action in rehabilitated members through lap splicing and dowel bars, complemented by cast-in-place connections using UHPC to minimize splice length and strengthen potential weak areas under external loads. The efficacy of this jacketing approach was rigorously evaluated through cyclic loading experiments on two RC frame specimens. Results indicated that the UHPC rehabilitation method not only recovered but significantly enhanced the seismic performance of the previously damaged frame, improving initial stiffness, yield strength, peak strength, displacement ductility, and energy dissipation capacity. However, the rehabilitated frame showed a reduced yield drift and increased residual displacement compared to the as-built frame. The experimental results also revealed the necessity of accounting for bond slip in structural rehabilitation analysis and design to prevent overestimating lateral stiffness. Furthermore, the study developed a computational model that incorporates flexure, bond slip, and shear responses, aiming to effectively simulate the load-displacement behavior of rehabilitated RC frames with reasonable accuracy.

A comparative study of constitutive models for EPS foam under combined compression and shear impact loading for helmet applications

Virtual testing of helmets using finite element (FE) analysis can be a valuable tool during product development. Still, its usefulness is limited by the quality of the constitutive model of the energy-absorbing material, usually foam. Built-in constitutive models in commercial FE software are developed for traditional linear compression loading. However, modern oblique test methods load the foam in combined compression and shear. Therefore, we aim to evaluate to what extent built-in constitutive models in commercial FE software can represent Expanded Polystyrene (EPS) foam during combined compression and shear loading (CCSL). EPS foam is tested experimentally in a newly developed test rig for CCSL (V-test). The response is compared against the simulation using three different constitutive models available in LS-DYNA (M83, M126, and M181). The models are assessed by their ability to capture the correct response, focusing on how well the continuum models can capture the phenomenological events seen in the experiments. The results show that the models perform well in compression, as expected. However, we point out limitations in the shear response and significant limitations in the unloading response, both important for oblique helmet testing. Due to these limitations, we conclude that the existing models are inadequate for accurately simulating oblique helmet impacts. There is a clear need to develop and implement new constitutive models focused on capturing CCSL including the unloading. Additionally, frictional sliding was found to substantially influence the measured response in the V-test method. Minimizing interface sliding is therefore critical for isolating the material behavior.