Tension Compression Research Articles

Effects of Material Orientation and Degree of Deformation on the Tension–Compression Asymmetry of AA2024‒T4

Effects of Material Orientation and Degree of Deformation on the Tension–Compression Asymmetry of AA2024‒T4

Reverse Torque and Wear of Internal Connections of Metal-Based Abutments Under Cyclic Loading.

Evaluate the reverse torque values and wear of internal connections caused by metal-based zirconia abutments under cyclic loading. Thirty implants were divided into three groups (n = 10), based on connection systems: Interference-fit cone-screw (Cortical Master Flash MI Fit-MTA and Cortical Master Flash MI RP-MTB), and Internal hexagon (Cortical Titanium Master Connect AR-IH). Metal-based zirconia abutments were tightened into the implant, and zirconia crowns were bonded using resin cement. All specimens underwent cyclic loading at 300 N and 9 Hz for 1,000,000 cycles. Reverse torques were assessed postloading, and wear was analyzed using scanning electron microscopy (SEM). Statistical analysis employed one-way ANOVA for reverse torque and wear values, with significant differences assessed via the Tukey test (α = 0.05). Significant differences in reverse torque values were found among groups: MTA (24.9 N), MTB (24.1 N), and IH (14.4 N). The IH group showed higher mean wear values on the tension side (121.0) and compression side (112.6), with a wear difference of 8.4. The interference-fit cone-screw abutments demonstrated significantly reduced torque loss and morphology after cyclic loading, reflecting enhanced performance. Although the stability of the metal base zirconia abutments to the implants was accurate, clinicians should be cautious about torque loss and more wear when using internal hexagon connections.

Elastic–plastic bending analysis of beams with tension–compression asymmetry: bimodular effect and strength differential effect

Elastic–plastic bending analysis of beams with tension–compression asymmetry: bimodular effect and strength differential effect

The focal mechanism and field investigations of mining-induced earthquake by super-thick and weak cementation overburden strata fracturing

Mining-induced earthquake (MIE) is a non-natural earthquake induced by mining activities. In Ordos mining area, super-thick and weak cementation overburden strata (STWCS) are common occurrence in Jurassic coal seam overlying strata. To explain and quantify the focal mechanism and roof fracture characteristics of MIE under the STWCS, the surface subsidence, ground borehole televiewer imaging and microseismic monitoring technologies were used to observe the fracturing of STWCS. The relative moment tensor method was also used to explore quantify focal mechanism of MIE. The results show that the development height of rock fractures increases, and the STWCS start to break when the panel below retreats along goafs. During this period, the surface stepped subsidence increases rapidly, and MIEs with magnitude above 2.0 begin to appear. The inversion matrix is constructed with the relative moment tensor method to solve the source mechanism of coal mining microearthquakes. The matrix improves the inversion efficiency and accuracy, thus being suitable for solving the focal mechanism of MIE by roof breaking. When coal seam is mined under the STWCS, the dip angle of focal rupture surface is mainly between 0° and 30°, accounting for about 50% of the total. The seismic source is mainly featured with roof horizontal separation tension and roof rotation compression instability. During mining along goafs, the seismic sources displayed a tendency of upward expansion and the shear slip ruptures were more than that in the solid coal mining stage. The focal mechanism of the MIEs in Shilawusu Coal mine was caused by the primary and periodic tension rupture of the STWCS and shear slip rupture. With the continuous mining of the panel, there is still the possibility of another round of MIEs. The research results provide a reference for the prediction, risk assessment and disaster control of MIEs under extremely thick overburden strata.

Emergence of bimodulus (tension–compression asymmetric) behavior modeled in granular micromechanics framework

Many materials exhibit a bimodulus behavior which manifests as tension–compression asymmetry under uniaxial loading conditions. From the viewpoint of engineering analyses and design, attempts have been made to properly account for this asymmetry by defining bimodulus models under various multiaxial loading conditions. The models available in the literature propose a complex set of cases valid for different combination of tensile/compressive loading characterized in either strain or stress space based on classical continuum mechanics. The key drawback of these propositions is the attempt to reduce an inherently nonlinear problem to a simpler linear one in opposition to the clear evidence of loading dependency. Moreover, the proposed approaches are generally conceived in an orthotropic framework even though the material is initially isotropic. It is only upon the deformation that an apparent anisotropy is induced due to the tension–compression asymmetry, which cannot be considered in the initial, reference, configuration. Indeed, from a fundamental viewpoint, the emergence of the macroscale asymmetry and induced anisotropy has its roots in the microscale mechanics of an otherwise isotropic (or other) microstructure. To further expatiate the fundamental view, we exploit the granular micromechanics paradigm to present a simple continuum model within the isotropic framework in reference configuration. Using this approach, the macroscale tension–compression asymmetry and induced anisotropy is shown to emerge naturally without the inconsistencies observed in the methods proposed in the literature.

The Derivation of CRSS in pure Ti and Ti-Al Alloys

The work focuses on the determination of the critical resolved shear stress (CRSS) in titanium (Ti) and titanium-aluminum (Ti-Al) alloys, influenced by an array of factors such as non-symmetric fault energies and minimum energy paths, dislocation core-widths, short-range order (SRO) effects which alter the local atomic environment, and tension-compression (T-C) asymmetry affected by intermittent slip motion. To address these multifaceted complexities, an advanced theory has been developed, offering an in-depth understanding of the mechanisms underlying slip behavior. The active slip systems in these materials are basal, prismatic, and pyramidal planes, with the latter involving both 〈a〉 and 〈c+a〉 dislocations. Each slip system is characterized by distinct Wigner-Seitz cell configurations for misfit energy calculations, varying partial dislocation separation distances, and unique dislocation trajectories—all critical to precise CRSS calculations. The theoretical CRSS results were validated against a comprehensive range of experimental data, demonstrating a strong agreement and underscoring the model's efficacy.

Leveraging Biotensegrity for Sports Performance: An Ecological Dynamics Perspective

Traditional sports science methods typically adopt reductionist approaches, focusing on isolated components of performance. Whilst insightful, reductionist approaches often fail to capture the interconnected nature of athletic movements and environmental interactions. In recent decades, two more holistic approaches, ecological dynamics and biotensegrity, have emerged. Ecological dynamics merges nonlinear dynamical systems theory with ecological psychology, delving into the intricate interplay among an athlete’s perceptual experiences, coordination patterns, and the dynamic sporting environment, providing a contemporary framework for exploring goal-directed behaviour and human adaptability. Biotensegrity, rooted in the tensegrity model, offers a holistic view of body posture and movement, emphasising the distribution of forces and signalling through a dynamic, multi scale network of continuous tension and discontinuous compression. By synthesising biotensegrity with ecological dynamics, we can cast new light on elite sports performance, highlighting the pivotal role of perception-action coupling in athlete-environment interactions. Here, we explore the potential value of integrating these two highly compatible perspectives, with the goal of contributing towards the advancement of athletic performance across various sports disciplines. This integrative framework offers a flexible, nuanced, and individualised approach to understanding sports performance, and represents a promising and relatively uncharted territory in sports science, inviting further research and practical applications.

Investigation of Fatigue Assessment Method for Glass Fiber Reinforced Composite Hull Structures Based on Stiffness Degradation

A study was conducted on the fatigue assessment method for composite ship structures under complex marine environments, and a fatigue assessment method based on the principle of stiffness degradation was proposed. Fatigue tests were performed on the composite material of the target ship to obtain the stiffness degradation parameters under tension–compression loading. Four fatigue hotspot areas in the midsection of the hull were selected, and mesh refinement was applied to these locations to accurately capture the variations in stress gradients. The structural stress response transfer function was calculated, and the short-term and long-term distribution data of wave loads were obtained. Finally, the fatigue life of the target ship hotspots was predicted by combining spectral fatigue analysis with the stiffness degradation theory. The results indicate that the connection between the bulkhead stiffener and the inner bottom plate has the shortest fatigue life, and its dimensions were optimized.

Study on Mechanical Characteristics of Discontinuous Cut-Off Wall of Dam Foundation Based on Plastic Damage Calculation Method

Dam foundations are prone to leakage damage after being exposed to long-term water action, which seriously affects the operation safety of the dam. At present, concrete cut-off walls serve an important means of anti-seepage for dam foundations. However, due to construction challenges, the cut-off wall needs to be poured segment-by-segment during the construction process, and the joints between adjacent segments become weak parts for seepage prevention. Therefore, it is crucial to clarify the stress state of segmented discontinuous concrete cut-off walls. Based on the Lee-Fenves framework and the tension–compression constitutive relationship of fracture energy, a plastic damage calculation method was established in this paper to characterize the mechanical behavior of discontinuous cut-off walls. The method was then used to analyze the mechanical performance of discontinuous walls with segment joints containing slurry cake. The research results showed that compared to the continuous cut-off wall, the vertical settlement in the middle part of the discontinuous cut-off wall increased by 5.8%, and the displacement along the river flow direction decreased by 35.3%. As the wall segment width decreased, the joint opening and the degree of tensile damage were reduced accordingly, while the compressive damage in the middle and lower parts of the wall was intensified. As the wall depth decreased, the constraints and load on the bottom of the wall showed obvious changes, leading to a reduced stress and damage level of the wall. The findings provide reference for the design and safety control of cut-off walls.

Unified characterization of failure surfaces and golden-ratio ductile-to-brittle classification for isotropic materials

The failure surface, often referred to as the failure angle, defines the specific planar orientation within a material that reaches its load-carrying capacity, represented by material strengths. Analyzing this critical surface is elemental for material characterization, providing profound insights into ductility and brittleness. Despite the diversity of methodologies employed for determining the failure plane from various criteria, a universally accepted theory that systematically governs this characteristic across a broad spectrum of isotropic materials remains elusive. Therefore, this paper aims to develop a unified framework for predicting the failure surface for all homogeneous isotropic solids by considering the convergence of three key material constitutive models: elasticity, failure, and plasticity. A universal energy-based failure criterion is utilized to determine failure angles under fundamental loading scenarios, including uniaxial tension, uniaxial compression, pure shear, and biaxial tension–compression. The sliding, splitting, and crushing behaviors are obtained from the direct and shear strain increments, while the ratio of the two strain increments elucidates the dominant roles in ductile and brittle failure modes. For the first time, the developed theory links the failure angle to Poisson’s ratio, and uniaxial strength properties, unveiling a connection between intrinsic material parameters and extrinsic ductility and brittleness induced by external loadings. The failure angle representing ductile-to-brittle transition under the applied stresses in the principal stress coordinates is shown to be directly related to the golden ratio and independent of loading types. This research addresses longstanding mysteries by providing a deeper understanding of the physics of solids and suggesting potential applications with a phase-field model for predicting the evolving fracture direction.

Fracture toughness of fibre failure modes in laminated composites under dynamic loading

Abstract The fracture toughness regarding fibre tensile failure and fibre compression kinking was measured using compact tension and compact compression specimens on a uniaxial bi-directional electromagnetic Hopkinson bar system. During the dynamic tests, the strain/displacement fields were monitored using the digital image correlation technique with a high-speed camera. Digital and scanning electron microscopy were used to investigate the fracture faces of the tested specimens. The initial fracture toughness for fibre tensile failure under quasi-static and dynamic loading was 166 kJ/m2 and 113 kJ/m2, respectively. For fibre compression kinking, the initial fracture toughness was approximately 120 kJ/m2 for both loading conditions. Less fibre pull-out may be responsible for the decrease in fracture toughness for fibre tensile failure under dynamic loading. Whereas for fibre compression kinking failure, there was no significant difference in the fracture faces of the damaged specimens at different loading rates.

An experimental investigation of fatigue performance and damage distribution mechanism in Bi-Directional GFRP composites

This study presents an experimental investigation of the fatigue performance and damage distribution mechanism of bi-directional GFRP composites. Uniaxial fatigue tests have been conducted under load-control, at stress ratios, R = 0.1, 0.5 and critical stress ratio (χ=-0.9). The influence of gauge length and surface roughness on fatigue life has been examined for R = 0.1. An infrared (IR) camera is employed to monitor temperature evolution and capture thermal images during the fatigue experiments. Fatigue stiffness degradation, energy dissipated per cycle, and severity of damage progression have been analyzed to elucidate the effects of stress levels and mean stress on fatigue performance. At higher stress levels, the damage is intense and localized, resulting in relatively shorter life due to fiber-breakage accompanied by rapid fatigue stiffness degradation. At lower stress levels, the damage is uniformly distributed and less severe, primarily involves stress concentration, resulting in longer fatigue lives. The study highlights the contrasting damage progression mechanisms for tension–tension and tension–compression fatigue. Under tension–tension fatigue, an oval-shaped damage zone forms perpendicular to the loading direction indicating transverse crack propagation, while under tension–compression fatigue, the damage zone aligns parallel to the loading direction indicating longitudinal crack propagation due to compressive loading.

Numerical modelling of complex modulus tests on asphalt concrete using the 2D discrete element method

The VENoL analytical model was developed to reproduce the nonlinear viscoelastic behaviour of asphalt concrete in dynamic analysis. In this paper, it is integrated as a contact law in a 2D model using the discrete element method (DEM). The asphalt concrete is modelled on a macroscopic scale. The VENoL model is applied in the numerical code without any recalibration of its analytical parameters. Particular attention is paid to modelling variations in the Poisson’s ratio as a function of test conditions. This integration is checked by comparing the results of the numerical model with those extracted from the literature for complex modulus tests in direct tension–compression. Despite the use of a macroscopic scale, it appears that the model can reproduce porosity effects through the mechanisms of DEM. Using the same set of parameters, two-point bending tests are also conducted to ensure their compliance in the characterisation of bituminous mixes.

Spatial distribution of soil pore structure and response characteristics of physical parameters in the subsidence area induced by shallow-buried extra-thick coal seam mining

The development of ground fissures in the subsidence area induced by shallow-buried extra-thick coal seam mining leads to a decrease in soil water-holding capacity and vegetation withering. The investigation of the spatial distribution characteristics of soil pore structure in mining-induced subsidence areas and the elucidation of the response mechanism between soil physical parameters and soil structure are essential prerequisites for achieving effective ecological environment protection and restoration in mining areas. In this study, three-dimensional visualization reconstruction of soil porosity, pore diameter, roundness rate and pore connectivity at different profile depths in subsidence area caused by ultra-thick coal seam mining was conducted by using the soil CT scanning technology. Additionally, a correlation analysis model was established between physical parameters such as soil moisture content, bulk density, and pore structure parameters. The results indicate that: (1) Compared to the non-subsidence area, the number, size, and proportion of soil pores significantly increase in the tension zone, compression zone, and neutral zone, and the pore network and connectivity are extensively interconnected, and the fissure development in the tension zone is most significant, and the soil pores in the subsidence compression zone are concentrated on one side due to the influence of soil deformation. (2) As the depth of the soil profile increases, the level of soil pore development significantly decreases. The large profile depth (40–100 cm) causes a significant decrease in pore development. (3) There is a significant correlation between soil pore structure parameters and soil physical parameters (P ≤ 0.05), a highly significant correlation between soil pore structure parameters and soil moisture content (P ≤ 0.01), and a highly significant correlation between soil texture and soil moisture content (P ≤ 0.01). This research is of great significance for guiding underground production layout and repairing damaged soil.

Types and application of auxetic cells: A review

Auxetic materials and structures have been largely regarded because of their superior mechanical properties compared to other structures. These materials and structures contract (expand) laterally under uniaxial compression (tension). In this study, we have investigated different types of auxetic cells such as reentrant, chiral and non-chiral, rotating polygonal, and etc. Also, we have described their mechanical properties in a separate section. The applications of these cells were also investigated in various fields of automotive, medical and etc. In this study, in addition to previous works, recent works have also been introduced. Being a comprehensive reference for different types of auxetic cells, this study helps researchers design various auxetic structures.

Toward a Test-Based Methodology to Evaluate Unrestrained Torso Neck Braces Using the Hybrid III ATD and MATD Neck

<div>The introduction of unrestrained torso neck braces as a safety intervention for helmeted motorcycle riders has introduced a set of unsolved challenges. Understanding the injury prevention afforded by these devices depends on a reliable test methodology by which to critically evaluate their efficacy against the most common mechanisms of neck injury. An inverted pendulum test is proposed to evaluate compression flexion (CF), tension flexion (TF), and tension extension (TE) of the neck using a Hybrid III anthropomorphic test device (HIII ATD) neck and a motorcycle-specific ATD (MATD) neck. In addition to investigating methods to quantify the beneficial effects of a neck brace, potential adverse effects of such a device are evaluated by measuring and evaluating relevant neck response measures. To that end, measured data using a current neck brace were analyzed and applied to various injury criteria related to the ATD neck used to compare the injury risk predicted by each parameter. The HIII ATD neck allows for a more conservative evaluation due to its exaggerated response in compression and may be more suitable in evaluating the neck injury criterion and injury risk in CF loading for low energy impacts. The MATD neck is limited to certain impact modalities, particularly the uncoupled behavior between head and neck during hyperextension, and individual neck measures at lower impact energy due to its limited structural integrity in direct head impacts. In the proposed tests, injury mechanisms were initially associated with a pre-impact head orientation and expected head and neck motion. However, these associations are not definitive. Although the most relevant neck injury mechanisms related to the unrestrained torso were addressed, the authors suggest that the presented tests are supplemented by a method to evaluate higher energy vertex impacts as a means to determine a neck brace’s efficacy during this loading modality.</div>

Design, Evaluation, and Implementation of a Novel Magnetic Resonance Imaging-Compatible Physiologic Loading Simulator for Ex-Vivo Joints.

Quantitative magnetic resonance imaging (qMRI), in combination with mechanical testing, offers potential to investigate how loading (e.g., from daily physical exercise) is related to joint and tissue function. However, current testing devices compatible with magnetic resonance imaging (MRI) are often limited to uniaxial compression, often applying low loads, or loading individual tissues (instead of multiple), while more complex simulators do not facilitate MRI. Hence, in this work, we designed, built and tested (N = 1) an MRI-compatible multi-axial load-control system, which enables scanning cadaveric joints (healthy or pathologic) loaded to physiologically relevant levels. Testing involved estimating and validating physiologic loading conditions before implementing them experimentally on cadaver knees to simulate and image gait loading (stance and swing). The resulting design consisted of a portable loading device featuring pneumatic actuators to reach a combined loading scenario, including axial compression (≤2.5 kN), shear (≤1 kN), bending (≤30 N·m) and muscle tension. Initial laboratory testing was carried out; specifically, the device was instrumented with force and pressure sensors to evaluate loading and contact response repeatability in one cadaver knee specimen. This loading system was able to simulate healthy or pathologic gait with reasonable repeatability (e.g., 1.23-2.91% coefficient of variation for axial compression), comparable to current state-of-the-art simulators, leading to generally consistent contact responses. Contact measurements demonstrated a tibiofemoral to patellofemoral load transfer with knee flexion and large contact pressures concentrated over small sites between the femoral cartilage and menisci, agreeing with experimental studies and numerical simulations in the literature.

Viscoelastic–viscoplastic model with ductile damage accounting for tension–compression asymmetry and hydrostatic pressure effect for polyamide 66

This paper proposes a model for predicting the complex inelastic mechanical response of polyamide 66. Polyamide 66 is a semi-crystalline pressure-sensitive polymer that exhibits asymmetric yielding behavior, in which the yield strength is slightly higher in compression. With this in mind, an I1-J2 yield function considering the asymmetric behavior and the hydrostatic pressure effect is presented and integrated into a phenomenological viscoelastic–viscoplastic model accounting for ductile damage. The corresponding thermodynamic framework and constitutive laws are discussed. Then, an experimental approach is presented to identify the model parameters through mechanical tests with different loading paths to capture the active mechanisms. The experimental findings obtained from uni-axial and multi-axial (tension-torsion) mechanical tests and the numerical model are used in an optimization algorithm to identify the model parameters. A parametric analysis is performed to study the effect of the asymmetric behavior on the state variables under different loading conditions using the identified parameters. The present model responses are in good agreement with the experimental data, and the combination of the experimental and numerical results demonstrates and states the asymmetric behavior of polyamide at relative humidity (RH) of 50%, which is captured by the suggested model. It is also worth pointing out that the parametric study conducted on a notched plate using finite element simulations showcases the structural computation capabilities of the proposed model.

Contribution of the Self‐Heating Method in the Characterization of the Fatigue Damage of Materials With Defects Resulting From Additive Manufacturing

ABSTRACTThis paper investigates the ability of the self‐heating method to characterize the fatigue behavior of 316L stainless steel produced by Laser Powder Bed Fusion. Nearly dense cylinders are built vertically using various process parameters corresponding to various volumetric energy densities. Fatigue specimens are then machined from these cylinders and polished. Fully reversed tension–compression fatigue tests (R = −1) are conducted. The self‐heating method is used for the estimation of the fatigue limits. These fatigue limits are compared to results obtained from S‐N curves in the high cycle regime. Whatever the set of process parameters, the self‐heating curves show three distinct domains of heat dissipation. Thanks to microstructure analysis, fractographic observations, and correlations with S–N curves, these domains can be closely linked to damage mechanisms associated or not with defects.

The effects of CNT type, alignment and dopants on piezoresistance in CNT fibres

Carbon nanotube fibres (CNTF) are piezoresistive, hence heralded as deformation sensors in applications ranging from flexible touch sensors to artificial skins and robotics. This work studies the piezoresistive behaviour of a wide range of CNT fibres from different sources, processing routes and microstructures. It provides a unifying view of the factors controlling piezoresistance in CNT fibres and related nanocarbon networks. We clarify the role of alignment and concentration of dopants and the constituent CNT type, demonstrating that the origin of piezoresistance in aligned fibres is the direct deformation of the constituent nanotubes, therefore, it is governed by the bulk modulus and thus the degree of CNT alignment. Doping through intercalation, which does not affect modulus or CNT separation, is detrimental to piezoresistive sensing, reducing the gauge factor proportionally to its decrease in resistivity. Aligned fibres show a quasi-linear piezoresistive response, with a positive change in resistance for all deformation modes applied: axial tension, axial or transverse compression. The axial gauge factor is shown to be proportional to fibre Young's modulus, with values of 2–9 for fibres spun from aerogels and above 30 for undoped fibres spun from liquid crystal solutions, respectively. Piezoresistance is attributed to the formation of internal barriers for conduction between metallic regions, which arise from the heterogeneous stress distribution along individual CNTs inherent in shear lag-type stress transfer. Commercial multifilament CNT yarns with a high degree of alignment and a format amenable for integration in large structures have demonstrated the piezoresistive gauge factors of 4 and sufficient sensitivity at strains below 1 % suitable for structural health monitoring of engineering structural composites.