Multiaxial Loading Conditions Research Articles

Utilizing Dynamic Analysis in the Complex Design of an Unconventional Three-Wheeled Vehicle with Enhancing Cornering Safety

Current trends in the transportation industry prioritize competitive rivalry, compelling manufacturers to prioritize concepts such as quality and reliability. These concepts are closely associated with public expectations of safety, vehicle lifespan, and trouble-free operation. However, the public must recognize that a vehicle weighing several hundred kilograms, moving at a non-zero speed, only contacts the road surface through a few points (depending on the number of wheels), each no larger than a human palm. Therefore, it is imperative to operate the vehicle in a manner that optimizes the behavior of these contact points. There are situations where drivers find themselves requiring dynamic vehicle handling, often unpredictable with a high degree of uncertainty. Rapid changes in direction become necessary in these cases. Such maneuvers can pose a significant risk of rollover for three-wheeled vehicles. Hence, the vehicle itself should contribute to increased ride safety. This paper presents key findings from the development of an unconventional three-wheeled vehicle utilizing the delta arrangement. Rollover safety for three-wheeled vehicles is currently well-managed, thanks to the utilization of electronic or mechatronic systems in delta-type vehicles to enhance stability. However, these systems require additional components. In contrast, the proposed control system operates solely on a mechanical principle, eliminating operational costs, energy consumption, maintenance expenses, and similar factors. The study also explores the absence of equivalent suspension and steering systems for front-wheel steering. Such designs are lacking in both practical applications and theoretical realms. Analytical and simulation calculations are compared in this study, highlighting the effectiveness of the newly proposed control system in enhancing stability and safety compared to conventional front-wheel suspension systems. Simulation programs provide more realistic results than analytical calculations due to their ability to account for dynamic effects on vehicle components and passengers, which is practically unfeasible in analytical approaches. Furthermore, this study focuses on investigating the fatigue life of material frames subjected to dynamic loading, which is a crucial aspect of ensuring safety. It is essential to have various testing devices to examine the fatigue life of materials under both uniaxial and multiaxial loading conditions. However, obtaining experimental results for fatigue life measurements of specific materials, which can be directly applied to one’s research, poses significant challenges. Hence, the proposed testing device plays a vital role in measuring material fatigue life and advancing the development of unconventional transportation methods. The information about the original testing device aligns perfectly with the article’s emphasis on dynamic analysis. The ultimate objective of all these efforts is to put the vehicle into practical operation for commercial utilization.

Micromechanical analysis of age‐induced strength reduction in a multiaxially loaded short‐fiber reinforced thermoplastic

AbstractIn this study, we demonstrate that the strength of a short‐fiber reinforced polymer as measured in uniaxial tension is not a good indicator for its strength under multiaxial loading conditions. To illustrate this fact, the influence of physical aging on the strength of a 20 wt% short‐fiber reinforced polycarbonate is studied for a uniaxial and biaxial loading condition. Results demonstrate that aging strongly reduces the strength in multiaxial loading, whereas, it increases in uniaxial loading. To rationalize these observations, a micromechanical analysis of the local stress state is performed using three‐dimensional (3D) representative volume elements (RVE) in combination with a constitutive model that adequately describes the intrinsic deformation response of the matrix. RVE simulations demonstrate that biaxial loading results in higher local hydrostatic stresses and triaxiality than the uniaxial loadcase for the composite system considered, and aging results in a shift towards higher values. The high triaxiality, the magnitude of the hydrostatic stress, and the shift in hydrostatic stress upon aging, presents a clear rationalization why physical aging induces a strength reduction in biaxial loading and not in uniaxial loading. These results highlight that care should be taken when predicting strength under complex loading conditions with only uniaxial data available.

Study on the Yield Behavior of Closed-Cell Foams under Multiaxial Loads Based on Different Yield Definitions

In this paper, the yield behavior of closed-cell foams under multiaxial load conditions is investigated via finite element analysis on the representative volume element (RVE) scale by using the regular Kelvin of RVE and random models of RVE, respectively. Several different definitions of yield are considered in the study. By benchmarking the simulations with the experimental data in the literature, it is shown that the elastic energy criterion is shown to be suitable for the definition of the yield point of closed-cell foams under different stress states. Based on the micro-scale elastic energy, which can be readily obtained by numerical simulation, a general yield definition is proposed to determine the yield behavior of the closed-cell foam materials at macroscopic scales. To test the adaptability of this general yield definition, we analyze multiple random models with different relative densities and inner structures. The results indicate that this general yield definition method can be used for different models, even applied to continuum materials.

Multi-axial elastic–viscoplastic curves of unidirectional carbon nanotube-polymer nanocomposites considering interphase and interface debonding using finite element modeling

This paper aims to predict the elastic-viscoplastic curves of unidirectional carbon nanotube (CNT)-reinforced polymer nanocomposites under the multi-axial tensions, including bi-axial transverse-transverse, bi-axial longitudinal-transverse and tri-axial longitudinal-transverse-transverse loadings by the use of finite element (FE) modeling. The role of the interphase between the CNT and polymer matrix as well as the debonding at the CNT/interphase interface in the stress-strain curves of nanocomposites is investigated. The polymer matrix and interphase region are characterized as elastic-viscoplastic materials, while the CNT behaves as the elastic material. The present results in uni-axial loading are compared to the available numerical outcomes for indicating the accuracy of the FE modeling. The simulation of multi-axial load conditions is based on the three-dimensional representative volume element (RVE) of the unidirectional CNT-polymer nanocomposite. The effect of interface strength on the elastic-viscoplastic stress-strain curves is examined under bi-axial and tri-axial loadings.

High-Cycle Fatigue Behavior of D2 Wheel Steel under Uniaxial and Multiaxial Loading Conditions for Potential Applications in the Railway Industry

This study investigates the fatigue damage evolution mechanisms of D2 wheel steel under high-cycle uniaxial and multiaxial loading conditions, with a focus on determining the fatigue crack growth threshold (FCGT). Uniaxial and multiaxial FCGT tests were performed on pre-cracked D2 wheel steel specimens subjected to high-frequency cyclic loading at stress ratios (R) of 0.1. The results indicate that the FCGT for D2 wheel steel under uniaxial loading conditions ranges between 8–9 MPa.m0.5, while under multiaxial loading conditions, it ranges between 6–9 MPa.m0.5. Scanning electron microscopy analysis revealed differences in the crack propagation mechanisms between the uniaxial and multiaxial tests, with cracks deviating from their path and following the microstructure in the uniaxial tests, and cracks propagating along planes of weakness in the multiaxial tests. These findings provide insights into the high-cycle fatigue behavior of D2 wheel steel under different loading conditions for potential applications in the railway industry.

A refined finite element model for UHPC-filled FRP tube column

A sound finite element model is essential for the nonlinear structural analysis of FRP tube-confined UHPC columns, wherein an accurate constitutive model to characterize the mechanical behavior of UHPC under passive constraints is of utmost importance. This study presents a refined finite element modeling methodology for the UHPC-filled FRP tube column. The constitutive model for UHPC under passive constraint is developed, in which the yield criterion, hardening/softening law, plastic flow rule, and damage evolution law are determined based on the experimental results of UHPC under multiaxial loading conditions. Furthermore, a solid element model of FRP tube with definable layer information is utilized to simulate the behavior of FRP tubes under complex stress states. The proposed finite element model is implemented in ABAQUS and verified through available experimental results. The results indicate that the proposed model can accurately predict the stress–strain behavior of confined UHPC with varying fiber and coarse aggregate contents, and describe the damage progression of UHPC and FRP tubes. Particularly, the interaction process between FRP and UHPC can be well reflected. The proposed finite element model serves as a paradigm for numerical analysis of UHPC-filled FRP tube elements and provides a reference for simulations of UHPC structures.

Fatigue strength and life prediction of lower limb venous stents under three-stage loading conditions

After the implantation of lower limb artery stents, the complex loading conditions imposed on the limb can lead to fatigue failure, which may induce inflammation and restenosis. To investigate the effect of multi-axial loading conditions on the fatigue performance of stents, five stents, namely APsolute Pro (APbott Vascular, USA), Complete SE (Medtronic, USA), Protégé EverFlex (PE3, USA), Pulsar-35 (Biotronik, Germany), and E-luminexx-B (Bard, USA), were analyzed based on the finite element method (FEM). Besides, their fatigue strength was determined under three levels of loading conditions, including tension-bending-torsion and compression-bending-torsion. Based on that, the fatigue life of these stents was predicted. The results showed that based on the nominal stress method, tension-bending-torsion loading had a more significant impact on the fatigue life of stents than compression-bending-torsion loading. Besides, two different types of initial cracks were analyzed by the fracture mechanics method. The results suggested that both the initial crack and the external load were the main causes of stent fatigue fractures. Compared with the loading nature, the influence of the initial crack on stent fatigue life was more significant. Under the same loading condition, the APsolute Pro stent had the longest fatigue life, while the E-luminexx-B stent had the shortest. Moreover, the mechanism of stent fatigue failure was revealed by exploring the fatigue performance and life prediction of stents under complex loading conditions. These findings have important implications for improving the structural design of stents and their clinical selection.

Multiaxial non-proportional fatigue behaviour and microstructural deformation mechanisms of 9%Cr steel at elevated temperature

High-temperature components utilised in practical service are often subjected to multiaxial non-proportional loading due to their complex geometry. In the present study, a set of strain-controlled fatigue tests were conducted on P92 steel at 600 °C, including uniaxial, multiaxial proportional, and multiaxial non-proportional loading conditions. Results reveal that the axial and shear stresses exhibit varied responses to the different non-proportionalities, with proportional loading resulting in the shortest fatigue life when the strain ratio is small. The non-proportional loading induces accelerated cyclic softening at axial direction while the shear stress is enhanced. Electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) analysis indicate that the increased role of shear stress promotes the dislocation motion from the planar slip to cross-slip under non-proportional loading, which in turn facilitates the microstructure evolution. It is also important to note that the evident development of microstructure and the combined effect of more crack initiations and more secondary cracks contribute to the lowest fatigue life under proportional loading.

Simulation of Crack Nucleation in Materials with Regularly Arranged Spherical Pores Under Multiaxial Loading Conditions

Simulation of Crack Nucleation in Materials with Regularly Arranged Spherical Pores Under Multiaxial Loading Conditions

Simulation of crack nucleation in materials with regularly arranged spherical pores under multiaxial loading conditions

A numerical study of the initial stage of crack growth in a material containing spherical pores under multiaxial compression (constrained conditions) has been carried out using the finite element method. The influence of the pore spacing and the mechanical properties of the material on the fracture localization and the direction of crack growth has been analyzed. Both brittle and ductile materials were studied. It has been established that material properties and the mutual arrangement of defects have a significant influence on the direction of propagation of cracks arising on the stress concentrators (structure defects), up to mutually perpendicular directions (for uniaxial of the characteristic sizes of the region of influence of spherical pores on each other, beyond which the stress fields of the neighboring elements of the structure do not overlap. The dependences of the sizes of this area on the elastic characteristics of the matrix material are shown. The obtained results are relevant for obtaining numerical estimates of the duration of the initial stages of quasi- brittle fracture of ceramic-based heterophase materials, refractories in particular. Ill. 6. Ref. 26. Tab. 1.

Molecular Dynamics Simulations Correlating Mechanical Property Changes of Alumina with Atomic Voids under Triaxial Tension Loading

The functionalization of nanoporous ceramics for applications in healthcare and defence necessitates the study of the effects of geometric structures on their fundamental mechanical properties. However, there is a lack of research on their stiffness and fracture strength along diverse directions under multi-axial loading conditions, particularly with the existence of typical voids in the models. In this study, accurate atomic models and corresponding properties were meticulously selected and validated for further investigation. Comparisons were made between typical material geometric and elastic properties with measured results to ensure the reliability of the selected models. The mechanical behavior of nanoporous alumina under multiaxial stretching was explored through molecular dynamics simulations. The results indicated that the stiffness of nanoporous alumina ceramics under uniaxial tension was greater, while the fracture strength was lower compared to that under multiaxial loading. The fracture of nanoporous ceramics under multi-axial stretching, was mainly dominated by void and crack extension, atomic bond fracture, and cracking with different orientations. Furthermore, the effects of increasing strain rates on the void volume fraction were found to be similar across different initial radii. It was also found that the increasing tension loading rates had greater effects on decreasing the fracture strain. These findings provide additional insight into the fracture mechanisms of nanoporous ceramics under complex loading states, which can also contribute to the development of higher-scale models in the future.

Multiaxial fatigue life prediction for various metallic materials based on the hybrid CNN‐LSTM neural network

AbstractA new algorithm optimization‐based hybrid neural network model is proposed in the present study for the multiaxial fatigue life prediction of various metallic materials. Firstly, a convolutional neural network (CNN) is applied to extract the in‐depth features from the loading sequence composed of the critical fatigue loading conditions. Meanwhile, the multiaxial historical loading information with time‐series features is retained. Then, a long short‐term memory (LSTM) network is adopted to capture the time‐series features and in‐depth features of the CNN output. Finally, a full connection layer is used to achieve dimensional transformation, which makes the fatigue life predictable. Herein, the hyperparameters of the LSTM network are automatically determined using the slime mold algorithm (SMA). The test results demonstrate that the proposed model has pleasant prediction performance and extrapolation capability, and it is suitable for the life prediction of various metallic materials under uniaxial, proportional multiaxial, nonproportional multiaxial loading conditions.

Failure Strength of Automotive Steering Knuckle Made of Metal Matrix Composite

This article presents the static performance of composite steering knuckle due to drive on an equivalent road, including different types of roughness and maneuvers. To achieve this purpose, the driving of a full-vehicle model was simulated using the multi-body dynamics (MBD) method, and the imposed loads on connection points of the steering knuckle to different components of the suspension system were extracted considering various maneuvers. Next, CATIA software was used to prepare a smooth model of the steering knuckle by employing coordinate measuring machine (CMM) data. Stress analysis was performed under the maximum value of the loading history in finite element (FE) software. Eventually, the safety factor was calculated based on some well-known criteria for static failure of the composite materials. Moreover, the optimum value of tungsten carbide as a reinforcing substance in aluminum composite was estimated to increase failure strength. The results show that an increase in tungsten carbide leads to an increase in the strength of the steering knuckle under purely axial loads (normal stress criterion) and also that an increase in this substance leads to a decrease in the strength of the part under shear loads (shear stress criterion). Therefore, based on the nature of the loads (i.e., multi-axial non-proportional random amplitude loading conditions) applied to the automotive steering knuckle due to actual conditions, this metal matrix composite (aluminum matrix and tungsten carbide as reinforcement) is not practical.

Three-dimensional full-field velocity measurements in shock compression experiments using stereo digital image correlation.

Shock compression plate impact experiments conventionally rely on point-wise velocimetry measurements based on laser-based interferometric techniques. This study presents an experimental methodology to measure the free surface full-field particle velocity in shock compression experiments using high-speed imaging and three-dimensional (3D) digital image correlation (DIC). The experimental setup has a temporal resolution of 100ns with a spatial resolution varying from 90 to 200μm/pixel. Experiments were conducted under three different plate impact configurations to measure spatially resolved free surface velocity and validate the experimental technique. First, a normal impact experiment was conducted on polycarbonate to measure the macroscopic full-field normal free surface velocity. Second, an isentropic compression experiment on Y-cut quartz-tungsten carbide assembly is performed to measure the particle velocity for experiments involving ramp compression waves. To explore the capability of the technique in multiaxial loading conditions, a pressure shear plate impact experiment was conducted to measure both the normal and transverse free surface velocities under combined normal and shear loading. The velocities measured in the experiments using digital image correlation are validated against previous data obtained from laser interferometry. Numerical simulations were also performed using established material models to compare and validate the experimental velocity profiles for these different impact configurations. The novel ability of the employed experimental setup to measure full-field free surface velocities with high spatial resolutions in shock compression experiments is demonstrated for the first time in this work.

A review on micromechanical modelling of progressive failure in unidirectional fibre-reinforced composites

The recent decades have seen various attempts at the numerical modelling of fibre-reinforced polymer (FRP) composites in the aerospace, auto and marine sectors due to their excellent mechanical properties. However, it is still challenging to accurately predict the failure of the composites because of their anisotropic and inhomogeneous characteristics, multiple failure modes and their interaction, especially under multiaxial loading conditions. Micromechanics-based numerical models, such as representative volume elements (RVEs), were developed to understand the progressive failure mechanisms of composites, and assessing existing failure criteria. To this aim, this review paper summarises the development of micromechanics-based RVE modelling of unidirectional (UD) FRP composites reported in the literature, with a focus on those models developed using finite element (FE) and discrete element (DE) methods. The generation of fibre spatial distribution, constitutive models of material constituents as well as periodic boundary conditions are briefly introduced. The progressive failure mechanisms of UD FRP composites simulated by RVEs under various loadings are discussed and the comparison of failure envelopes predicted by numerical results and classical failure criteria are reviewed.

On material-agnostic fatigue life prediction using Buckingham Pi Theorem

A robust, quantitative analysis is needed to prevent frequent, catastrophic failure of components in powerplants and aircraft, to cite but two examples, due to cyclic loading that could lead to fatigue failure. The model presented in this research will be useful in the reliable design and safe operation of components and equipment. A fatigue life (the dependent variable) prediction model, which employs both stress-based, and stress–strain based criteria is presented that uses the Buckingham Pi Theorem with the experimental parameters influencing fatigue behaviour taken as the independent variables. The validation of the model is done using reliable, frequently used uniaxial fatigue data, culled from the NIMS (National Institute for Materials Science, Tsukuba, Japan) fatigue database on important industrial alloys that experience fatigue loading in service. (No reliable data on such a scale were available to test the validity of this model under multi-axial fatigue loading conditions.) It is demonstrated that the model predicts the experimental results accurately. The accuracy of prediction is examined for every case and compared with that of some other existing methods. Moreover, the potential applicability of this analysis in areas not yet validated is examined.

Experimental and numerical investigation of the influence of multiaxial loading conditions on the failure behavior of clinched joints

Destructive testing methods are used to determine the joint characteristics of mechanical joining technologies by testing the joints under different types of loads. In real load cases, however, combined loading conditions arise in complex structures that cannot be investigated experimentally at present. The objective of this study is to adapt a so-called L-specimen geometry for mechanical joints to introduce combined peel and shear tensile loading, taking into account plastic pre-deformation of the joined parts. A new specimen geometry is presented to investigate three different clinched joints using different materials, namely HCT590X as well as EN AW-6014 T4. The load capacity behavior, as well as the failure behavior, is analyzed based on failure modes for pure shear, pure peel, and combined loading. Furthermore, the L-specimen is investigated by numerical simulation and compared with the experimental results.

Deformation and Damage Behavior of a 1Cr-Cast Steel Under Multiaxial Loading at Elevated Temperatures

Abstract Rising demands on material performance at high temperature in components under complex loading such as steam- and gas turbine housings require an increase in versatility and precision of component life modeling approaches. However, the database to calibrate those models is commonly derived from uni-axial testing. The impact of multi-axial loading, both proportional and nonproportional, is usually addressed theoretically by the use of equivalent stress/strain formulations or reduction ratios derived from few specific validation tests. Therefore, a research program which systematically investigates the fatigue life of a 1Cr-cast steel both experimentally and theoretically has been initiated recently. For the experimental part, cruciform specimens are tested in a servohydraulic biaxial test rig equipped with an induction heating device. Each experiment is accompanied with finite element simulations before and after the test to parametrize the loading condition and derive equivalent loading parameters at hot-spot locations. When assessing cycles until crack initiation in the experiments using the von Mises equivalent strain range, a reoccurring sequence in the impact of the axis ratio can be observed. Beside the fatigue life in terms of cycles to crack initiation, the multi-axial loading conditions may also affect the deformation behavior, in detail cyclic softening. Such effects are discussed by comparing the produced experimental evidence with results gained from a unified constitutive material model. Furthermore, different lifetime parameters are applied in order to judge their accuracy and suitability for design applications.

Strengthening Modulus and Softening Strength of Nanoporous Gold in Multiaxial Tension: Insights from Molecular Dynamics.

The functionalized applications of nanoporous metals place clear requirements on their basic mechanical properties, yet there is a lack of research on the mechanical response under multiaxial loading conditions. In this work, the mechanical behaviors of nanoporous gold under multiaxial tension are investigated via molecular dynamics simulations. The mechanical properties under different loading conditions are compared and the microstructure evolution is analyzed to clarify the deformation mechanisms of nanoporous gold in biaxial and triaxial tension. It is found that the modulus of nanoporous gold in multiaxial tension is strengthened and the strength is softened compared to uniaxial tension. The failure of nanoporous gold in multiaxial tension is dominated by the progressive yielding, necking, and rupture of ligaments along the multiple uniaxial loading directions. The dislocation activity under multiaxial loads is more intense and more prone to plastic deformation, ultimately resulting in lower strength and smaller failure strain. The findings provide more insight into the understanding of the deformation mechanisms of nanoporous metals under complex stress states.

Local buckling on large sandwich panels used in light aviation: Experimental setup and failure scenarios

The design of light aircraft sandwich structures is driven by a local buckling phenomenon named “wrinkling” which can be the primary cause of failure of such structures. Structural tests using the VERTEX methodology were performed to access the wrinkling behaviour of 558x536mm2 technological sandwich specimens representative of the design used in light aviation. The operating principle of the VERTEX machine is the use of four hydraulic actuators to load a rectangular box structure, the upper part of the central box being closed by the sandwich under test. Thus, sandwich specimens were tested under compressive and shear loading. A wrinkling scenario was identified thanks to Stereo Digital Image Correlation and a high-speed camera. Wrinkling localisation is driven by mechanical and geometrical aspects. Experiments on wrinkling in sandwich panels remain rare in the literature at this level of the test pyramid for certification of aeronautical structures. This upper scale presents some advantages as it allows multiaxial loading and boundary conditions consistent with a lightweight aeronautical structure. Technological elements can also be added to study their influence on the structure. The result will lead to interesting future investigations on the dialogue between experiments and models in a forthcoming paper.