Compressive Loading Conditions Research Articles

A Volume Averaging FEM-Based Fracture Model for Damage Process in Cohesive-Frictional Solids

In this study, a mesh-independent fracture model is implemented in the standard finite-element (FE) framework by leveraging a volume averaging approach. For the tension regime, a cohesive crack model is adopted for the onset and propagation of the crack, in which the direction of a new crack is defined as the eigenvector of the maximum principal stress. For the compression regime, the Coulomb criterion is considered for the onset and propagation of the crack, and the new crack direction is obtained based on the Mohr–Coulomb criterion by employing the residual friction angle. In addition, a new return mapping algorithm, i.e., the general return mapping, is developed for both compression and tension loading conditions to improve the numerical robustness, convergence, and accuracy. Finally, in order to validate the constitutive behavior, a stress-point calculation is performed, followed by boundary value problems to illustrate the robustness of the suggested return mapping algorithms and the mesh-independence effects of the volume averaging methodology.

Numerical Simulation and Experimental Study of Porous Titanium Implants under Compressive Loading Conditions

Numerical Simulation and Experimental Study of Porous Titanium Implants under Compressive Loading Conditions

Fatigue Life Prediction for the Skin Structures of Aircraft Sensor Pod Under Acoustic Load with Mean Stress

The skin structure of sensor pod mounted on the exterior of aircraft can be exposed to the acoustic dynamic load and static load such as aerodynamic pressure and inertial load during flight. Fatigue life prediction of structural model under acoustic load should be performed and also differential stiffness of model modified by static load should be considered. The acoustic noise test spectrum of MIL-STD-810G was applied to the structural model and the stress response power spectral density (PSD) was calculated. The frequency response analysis was performed with or without prestress induced by inplane static load, and the response spectrum was compared. Time series data was generated using the calculated PSD, and the time and frequency domain fatigue life were predicted and compared. The variation of stress response spectrum due to static load and predicted fatigue life according to the different structural model considering mean stress were examined and decreasing fatigue life was observed in the model with prestress of compressive static load.

Loading conditions impact on the compression fatigue behavior of filled styrene butadiene rubber

Abstract Fatigue failure, commonly encountered in rubber materials, is a critical issue. In this study, the compression fatigue tests of filled styrene-butadiene rubber (SBR) under different loading conditions were performed, applying cylindrical specimens. A stress–strain curve and modulus drop curves were generated by nine fatigue loading cases, covering different R ratios in the range of 0 < R < 1. The temperature variation in the process of compression fatigue was explored. Three different approaches were applied to investigate the fatigue life of the SBR (it is used twice hence abbreviation should be used) vulcanizates. These methods were validated in assessing the fatigue failure of the specimens. According to the experimental fatigue life, a fatigue life prediction model based on strain amplitude as the damage parameter was established. The results demonstrated that both R ratio and strain amplitude could affect the fatigue life. For all the loading cases, the fatigue life generally increases with the increase of R ratio. Under the compression loading condition, the narrower range of strain and the lower mean strain are beneficial to the fatigue resistance of rubbers, which also indicates a larger pre-load provides much higher fatigue resistance. During the fatigue loading, the temperature rises rapidly until it reaches a peak value, then drops slightly, and finally reaches a plateau.

Network-based modelling of mechano-inflammatory chondrocyte regulation in early osteoarthritis.

Osteoarthritis (OA) is a debilitating joint disease characterized by articular cartilage degradation, inflammation and pain. An extensive range of in vivo and in vitro studies evidences that mechanical loads induce changes in chondrocyte gene expression, through a process known as mechanotransduction. It involves cascades of complex molecular interactions that convert physical signals into cellular response(s) that favor either chondroprotection or cartilage destruction. Systematic representations of those interactions can positively inform early strategies for OA management, and dynamic modelling allows semi-quantitative representations of the steady states of complex biological system according to imposed initial conditions. Yet, mechanotransduction is rarely integrated. Hence, a novel mechano-sensitive network-based model is proposed, in the form of a continuous dynamical system: an interactome of a set of 118 nodes, i.e., mechano-sensitive cellular receptors, second messengers, transcription factors and proteins, related among each other through a specific topology of 358 directed edges is developed. Results show that under physio-osmotic initial conditions, an anabolic state is reached, whereas initial perturbations caused by pro-inflammatory and injurious mechanical loads leads to a catabolic profile of node expression. More specifically, healthy chondrocyte markers (Sox9 and CITED2) are fully expressed under physio-osmotic conditions, and reduced under inflammation, or injurious loadings. In contrast, NF-κB and Runx2, characteristic of an osteoarthritic chondrocyte, become activated under inflammation or excessive loading regimes. A literature-based evaluation shows that the model can replicate 94% of the experiments tested. Sensitivity analysis based on a factorial design of a treatment shows that inflammation has the strongest influence on chondrocyte metabolism, along with a significant deleterious effect of static compressive loads. At the same time, anti-inflammatory therapies appear as the most promising ones, though the restoration of structural protein production seems to remain a major challenge even in beneficial mechanical environments. The newly developed mechano-sensitive network model for chondrocyte activity reveals a unique potential to reflect load-induced chondroprotection or articular cartilage degradation in different mechano-chemical-environments.

Experimental and Numerical Study on the Mechanical Performance of Dou-Gong Bracket at the Corner under Vertical Load

ABSTRACT This paper is focused on the mechanical performance of the Dou-Gong bracket at the corner under vertical load. A full-scaled specimen was tested under the static compressive load. The load-displacement curves, load distribution law and displacement of components were discussed. A finite element model was established and validated with test results. The deformation and stress of the whole Dou-Gong bracket and main components were analyzed, and the influence of the wood properties and friction coefficients was studied. The results show that there are four stages in the load-displacement curve and the plastic stiffness is 76.36% lower than that in the elastic stage. The components in the oblique 45° direction mainly transfer the force, while the load distribution ratios in the width and oblique 45° directions of the lower layer is closer to 1. The displacements of the components in oblique 45° direction in the No. 2 and No. 3 layers are smaller than those of the components in width direction. With the increase of the compressive strength, the elastic moduli in the radial direction and the friction coefficients, the stiffness in the plastic stage increases and the maximum displacement decreases. However, the compressive strength and the elastic moduli in the longitudinal direction have little effect on the load-displacement curves.

Impact loading of additively manufactured metallic stochastic sheet-based cellular material

The mechanical response of additively manufactured sheet-based stochastic cellular materials under impact loading was investigated in this work. Samples with four different relative densities (13%, 16%, 19%, and 21%) were fabricated out of 316 L stainless steel using the powder bed fusion (PBF) additive manufacturing (AM) technique. The samples were then tested under quasi-static and dynamic (impact) compressive loading conditions to evaluate their mechanical behavior. All analyzed samples showed a similar progressive plateau stress behavior at all analyzed strain rates. The Crash Force Efficiency (CFE) values of samples at analyzed strain rates were in the range of 67–70%, indicating the uniformity of their mechanical response, which is a vital application feature. The samples exhibited excellent Specific Energy Absorption (SEA) capacity ranging between 5 and 9.2 J/g in the quasi-static deformation mode while achieving up to 35 J/g in the shock deformation mode. Thus, the proposed design approach has great potential for impact and blast mitigation applications. The first and second critical loading velocities of analyzed samples are proportional to the relative density and are in the range of 25–32 m/s and 43–56 m/s, respectively. Minor strain rate hardening was observed in quasi-static deformation mode, while a significant strain rate hardening was observed in shock deformation mode achieved by powder gun testing. The developed and validated computational models offered a more detailed analysis of the deformation mechanism and provided means to predict the sample's behavior at very high strain rates.

Mandrel Bend Test of Screen-Printed Silver Conductors

Abstract Flexible electronics are electronic devices and components that can be stretched, bent, twisted, and folded without losing their functionality. Flexible electronics is conformable, lightweight, easily tailorable, and low-cost, and thus, flexible electronics is increasingly being explored in health care, internet of things, automotive, aerospace, communication, safety, security, and food-related applications. Also, flexible electronics can now support increased functionality as well as various fabrication techniques. With an increased adaptation of flexible electronics, research is being conducted to better understand the failure mechanism of flexible electronics and thus improve their reliability and service life. In this paper, a cyclic mandrel bend test has been designed and carried out on printed conductors with PET and PI substrates. With the designed test apparatus, both tensile and compressive bend tests have been performed. Using a four-wire method, the resistance change of the printed conductors with different widths has been measured in situ under tensile and compressive loading conditions using mandrels with different radii. The results have been compared among different conductor widths, bending modes, and substrate materials. Besides, in situ SEM images have been taken to understand the failure mechanisms of the printed conductors. Based on the study, it is seen that there exists a direct correlation between the mandrel diameter, the damage in the printed conductor, and thus, the resistance change with cyclic mandrel testing. Also, it is seen that the damage under compressive bending mode is significantly lower than the damage under tensile bending mode.

Investigations into Nonlinear Effects of Normal Pressures on Dynamic Cyclic Responses of Novel 3D-Printed TPMS Bridge Bearings

Bridge bearings are one of the most important components in bridge systems. Typical bearings are extensively used in small- to medium-span highway bridges since they are economical and offer a good performance at service-level conditions. On the other hand, common bridge bearings possess a low performance-to-weight ratio under combined compression and shear loading conditions (low crashworthiness and specific energy absorption), due to their heavy weight, high costs, and the non-recyclability of steel and elastomer materials. With the help of a relatively higher ratio of a 3D-printed triply periodic minimal surface (TPMS) structure, this method can potentially be used for bridge bearing applications. However, the cyclic responses of this TPMS structure used in bearings have never been completely investigated. This study is the world’s first to investigate the effects of normal pressure on the cyclic responses of novel 3D-printed TPMS bridge bearings. A numerical TPMS unit cell model considering the effects of normal pressure on cyclic responses of a novel TPMS bridge bearing is developed and validated with experimental data. The numerical results reveal new insights related to the nonlinear effects of normal pressure on the cyclic behaviours of 3D-printed TPMS bearings. Higher normal pressures result in a higher degree of nonlinearity in the dynamic cyclic responses of the 3D-printed TPMS bearings.

Enhancement of Mechanical Properties Through Design Modification in Mechanical Metamaterials

Mechanical metamaterials draws everyone’s attention and expands its scope due to their exceptionally controllable mechanical properties, along with the advancement in additive manufacturing technology, which facilitates the easy fabrication of the metamaterial. The experimental survey presented in this document involves the design of the hybrid type model (Anti-tetra chiral) and its two variants with modified dimensions, simulation for the designed models for compressive loading conditions using loads 50N, 75N and 100N for each variant of varied dimensions. Inconel 718 material is considered for the simulation study. After simulations, the results obtained are transformed into graphical representation to further analyse the compressive strength that each model can withstand.. Key Words: Mechanical Metamaterials, Hybrid model, additive manufacturing technology

EXPERIMENTAL REPORT ON GLASS PANELS AGAINST STATIC AND REPEATED IN-PLANE COMPRESSION LOADING

Primary load-bearing members used in glass structures, such as columns consisting of glass panels, are frequently subjected to in-plane loading. Its allowable stress for safety design appears to be a significant subject. By analyzing the results of static (without repeated loading) and cycling compression loading tests, the authors explore the mechanical features and failure mechanism of the tempered glass panels subjective to in-plane compression loading, including its ultimate stress and buckling load. In addition, a statistical method based on the experimental results is adopted to evaluate the allowable compressive stress. The experimental results show that the ultimate loads of specimens with high slenderness ratios satisfy Euler's critical load formula. In contrast, the ultimate loads of specimens with low thickness ratios distribute in a certain variance range. For the cycling loading test, after 30 times of repeated loading with maximum stress equivalent to 2/3 of the ultimate static stress, the average strength is almost the same or bigger than that of static loading tests. No fatigue fracture due to repeated loading was found for the tempered glass panels. Consequently, the allowable stress for in-plane compressive loading can be formulated based on Euler's critical load formula for a glass panel with a bigger slenderness ratio. The formulation for the allowable compressive stress of a glass panel with a smaller slenderness ratio is promoted using statistical analysis with a 95 percent confidence level for the safety design.

Investigations of piles by bidirectional static loading test in Astana soils

The article presents the results of vertical static load tests of diametral and deep bored piles specially conducted at the construction site of EXPO-2017 in Astana, Kazakhstan. The methodology for determining the bearing capacity of the pile is summarized. Bored piles with a length of 31.5 m and a diameter of 1000 mm were tested. Vertical static load tests were conducted for the following load configurations: Bidirectional Static Loading Test (according to ASTM D8169), Static Compression Loading Test according to ASTM D1143-07 and Static Loading Test according to GOST 5686-12. The method presented in the paper can serve as practical guidelines to assess the capacities of bored piles installed in the field. This geotechnical investigation is important for understanding the soil-structures interaction on difficult soil ground conditions related to the construction sites.

The change of glass transition temperature under general stress state in amorphous materials

The phenomenon of the change in glass transition temperature (Tg) upon externally applied stresses in amorphous materials has been known for a long time. However, most of the existing works focus on the effects of hydrostatic stress state, while the effect of a general stress state on glass transition behaviors remains largely unknown. In this work, molecular dynamics (MD) simulations are first performed on typical amorphous polymers and alloys to probe the change of Tg under different stress states. It is found that Tg changes linearly with pure hydrostatic stress, while under shear stress, Tg changes nonlinearly with the stress magnitude. This further leads to an asymmetric change in Tg under uniaxial tension and compression loading conditions. Based on the above observations, a theoretical model based on the free volume theory and Eyring model is proposed to quantify the change of Tg under general stress states. Comparison with simulation results and existing experimental data reported in the literature demonstrate that the theoretical model can capture the stress dependence of Tg in amorphous materials. Potential applications in tuning Tg through external stress and the sensitivity of Tg to hydrostatic and shear stresses for different amorphous materials are subsequently discussed. The current work reveals the dependence of Tg on general stress states, pointing out potential routes to tune the mechanical properties of amorphous materials.

An efficient micromechanics-based finite element model for failure analysis of laminated composites

Accurately predicting ultimate strength of composite laminate is still a great challenge, especially only based on the constituent properties. In this paper, the micromechanics Bridging Model and systematic failure criteria for the constituent materials with emphasis on matrix failures subjected to three dimensional (3D) loads are compiled into a UMAT subroutine for ABAQUS to analyze failures of a laminated composite structure. The main purpose of this research is to greatly reduce calculation costs for loading conditions of in-plane tension or compression by introducing a simplified 3D finite element model based on the Pipes-Pagano theory. In all calculation cases, only the constituent properties together with the transverse tensile strength of unidirectional composite are needed as input data. Later in this paper, sufficient illustrations of 81 different composite laminates composed of 14 material systems are analyzed to confirm the practicability of this model.

Biomechanical comparison of different rod-to-rod connectors to a conventional titanium- and cobalt chromium posterior spinal fixation system

IntroductionSeveral types of rod-to-rod connectors are available for the extension of spinal fixation systems. However, scientific literature regarding the mechanical performance of different rod-to-rod connector systems is lacking. Research questionThe goal of this study was to evaluate the mechanical characteristics of axial and lateral rod connectors in comparison to a conventional pedicle screw rod (titanium and cobalt chromium) construct. Material and methodSix types of instrumentations were investigated in a standardized test model to quantify the mechanical differences: 1: titanium rod; 2: titanium rod with axial connector; 3: titanium rod with lateral connector; 4: cobalt chromium rod; 5: cobalt chromium rod with axial connector; 6: cobalt chromium rod with lateral connector. All groups were tested in static compression, static torsion and dynamic compression and statistically compared regarding failure load and stiffness. ResultsIn static compression loading, the use of connectors increased the construct stiffness, but unaffected the yield load. The use of a cobalt chromium rod significantly increased by approximately 40% the yield load and stiffness in comparison to the titanium rod configurations. Under dynamic compression, a similar or higher fatigue strength for all tested groups in comparison to the titanium rod configuration was evaluated, with the exception of titanium rod with axial connector. ConclusionBiomechanically, using rod connectors is a secure way for the extension of a construct and is mechanically equal to a conventional screw rod construct. However, in clinical use, attention should be paid regarding placement of the connectors at high loaded areas.

Numerical-experimental study on the compressive behaviour of repaired composite panels

Barely Visible Impact Damages (BVID) caused by impact phenomena during maintenance and in-service missions can be a critical issue for composite structures. BVIDs may induce delaminations and intra-laminar damages, which can considerably reduce stiffness and strength of composite laminates leading to component replacement or repair.This work is aimed to numerically and experimentally investigate the mechanical behaviour of a repaired aeronautical composite stiffened panel subjected to compressive loading conditions. A numerical activity has been performed by introducing Finite Element models in the ABAQUS FEM environment with the aim to numerically simulate the mechanical behaviour of the investigated stiffened panel configuration. Indeed, a pristine panel configuration and a repaired panel configuration have been numerically modelled. In the repaired configuration a stepped bonded patch has been used to simulate the repair process. Then, an experimental testing activity has been performed on the repaired stiffened panel configuration and experimental data have been compared to results obtained from the numerical studies for model validation purposes. The validated numerical model has been used to perform a sensitivity analysis on the compressive behaviour of repaired stiffened panels with patches to assess the influence of stacking sequence and sizes of the repair patches on the panel's mechanical behaviour. Although other components are involved in the tightness of the repair patch, the work proved that the stacking sequence of the patch play the main role in the effectiveness of the process in recovering the mechanical performances and overall behaviour of the component.

A regulatory role of Piezo1 in apoptosis of periodontal tissue and periodontal ligament fibroblasts during orthodontic tooth movement.

Investigation on the effect of Piezo1 on periodontal tissue and periodontal ligament fibroblasts (PDLFs) under mechanical stress and the underlying mechanism. The orthodontic tooth movement rat model was established via an orthodontic spiral tension spring. PDLFs were cultured and subjected to 2.0g/cm2 static compressive loading. Blocked the Piezo1 via Piezo1 inhibitor, GsMTx4. TUNEL staining and flow cytometry determined the apoptosis rate of periodontal tissue and PDLFs in rats. Expression of Piezo1, p-p38 and ERK1/2 was analysed by immunofluorescence assay and western blotting. Piezo1 inhibitor GsMTx4 relieved the increased expression of Piezo1, ERK1/2 and p-p38, and alleviated apoptosis in periodontal tissue and PDLFs under compressive loading. Piezo1 inhibition can alleviate force-induced apoptosis and damage in rats' periodontal tissue and PDLFs, and regulate the p38/ERK1/2 signalling pathway.

Bio-inspired Ti‐6Al‐4V mechanical metamaterials fabricated using selective laser melting process

In the current study, porous architecture of the Euplectella aspergillum has been used to mimic mechanical metamaterial. Modelled metamaterial are fabricated using selective laser melting (SLM) process with Ti-6Al-4V alloy. The fabricated metamaterials are mechanically tested under quasi-static compressive loading condition. The heat treatment effect on compressive behavior and microstructure is also observed. The as-printed metamaterial has strength (173.36 MPa) and fracture strain (2.96%), whereas heat-treatment decreases the strength to (146.08 MPa) and increases the fracture strain to (12.60%). The increase in ductility after heat treatment is due to the formation of β-Ti and decrease in residual stresses. The presence of β-Ti phase is confirmed using microstructural and X-ray diffraction method. X-ray diffraction also confirms the decrease in tensile residual stress value from (179.5 ± 4.5 MPa) for as-printed to (96.5 ± 2.4 MPa) after heat-treatment process. Normal residual stress value is also dependent on the location of measurement on the metamaterial. However, heat treatment and location of measurement have no effect on shear residual stress. In the last, finite element simulation has been carried out to visualize the effect of diagonal struts on the deformation behavior. The result shows diagonal struts in the E. aspergillum based metamaterial helps to prevent global buckling and uniformly distribute the load, hence improves the strength of the metamaterial. • 2D Metamaterials are derived from Euplectella aspergillum • Metamaterials are fabricated using selective laser melting process with Ti-6Al-4V alloy • Mechanical and fracture behavior of the as-printed and heat-treated samples is compared • Bio-inspired metamaterial shows improved buckling resistance properties • Residual stress decreases with heat treatment and it is dependent on the topology

Structural response and energy absorption assessment of corrugated wall mechanical metamaterials under static and dynamic compressive loading

Mechanical metamaterials, especially corrugated wall structure with negative Poisson's ratio, have received much attention since it offers more options for energy absorption. Herein, the effects of structure factors, wall thickness, and gradient design on the structural response and energy absorption performance of corrugated wall metamaterials have been explored using finite element simulations, quasi-static compression tests and dynamic plate-impact tests. The energy absorption performance was evaluated using indexes such as energy absorption efficiency, specific energy absorption, plateau stress, etc. The results show that the difference in the deformation and interaction mechanism between corrugated walls leads to different mechanical responses of the structure. Compared with the normal sample, the gradient setting of the wall thickness (t) increases the negative Poisson's ratio by 44.6%, and the gradient setting of the structure factor (h/L) increases the maximum energy absorption efficiency to 80.52% (an increase by 14.7%). Finally, plate-impact tests demonstrate that the corrugated gradient structure has better energy dissipation performance than the corrugated normal structure. Compared with the normal sample, the thickness gradient sample and the structure factor gradient sample reduce the impact load of the structure by 42.89% and 34.56%, respectively. This work can strengthen our capability of engineering tunable energy-absorbing device for a wide range of application.

Biomimicking Nature-Inspired Design Structures-An Experimental and Simulation Approach Using Additive Manufacturing.

Whether it is a plant- or animal-based bio-inspiration design, it has always been able to address one or more product/component optimisation issues. Today's scientists or engineers look to nature for an optimal, economically viable, long-term solution. Similarly, a proposal is made in this current work to use seven different bio-inspired structures for automotive impact resistance. All seven of these structures are derived from plant and animal species and are intended to be tested for compressive loading to achieve load-bearing capacity. The work may even cater to optimisation techniques to solve the real-time problem using algorithm-based generative shape designs built using CATIA V6 in unit dimension. The samples were optimised with Rhino 7 software and then simulated with ANSYS workbench. To carry out the comparative study, an experimental work of bioprinting in fused deposition modelling (3D printing) was carried out. The goal is to compare the results across all formats and choose the best-performing concept. The results were obtained for compressive load, flexural load, and fatigue load conditions, particularly the number of life cycles, safety factor, damage tolerance, and bi-axiality indicator. When compared to previous research, the results are in good agreement. Because of their multifunctional properties combining soft and high stiffness and lightweight properties of novel materials, novel materials have many potential applications in the medical, aerospace, and automotive sectors.