Stiffness Properties Of Materials Research Articles

Semi-active vibro-acoustic control of vehicle transmission systems using a metal rubber-based isolator

This work is concerned about employing a semi-active metal rubber (MR)-based isolator to suppress noise and vibration for vehicle transmission systems. The adaptive stiffness and damping properties of MR material play a key role in the semi-active control effect. In this regard, a particular automotive transmission component—precisely, a plate dedicated to accommodating bearings—has been selected as the focus of research to control its noise and vibration. A microcomputer-driven control system is applied, featuring characteristics such as high performance, compact size, lightweight design, and energy efficiency, which make it ideal for testing in the automotive sector. The efficacy of the devised control scheme is assessed through the deployment of accelerometers and sound intensity probes to quantify the vibrations and the radiated acoustic power, respectively. Interesting noise and vibration reduction rates are achieved using both open-loop and closed-loop strategies. This research opens the horizons to employ MR material in a semi-active configuration for industrial requirements surpassing its classical passive implementation, notably in terms of broadband attenuation performance.

Towards a unified nonlocal, peridynamics framework for the coarse-graining of molecular dynamics data with fractures

Molecular dynamics (MD) has served as a powerful tool for designing materials with reduced reliance on laboratory testing. However, the use of MD directly to treat the deformation and failure of materials at the mesoscale is still largely beyond reach. In this work, we propose a learning framework to extract a peridynamics model as a mesoscale continuum surrogate from MD simulated material fracture data sets. Firstly, we develop a novel coarse-graining method, to automatically handle the material fracture and its corresponding discontinuities in the MD displacement data sets. Inspired by the weighted essentially non-oscillatory (WENO) scheme, the key idea lies at an adaptive procedure to automatically choose the locally smoothest stencil, then reconstruct the coarse-grained material displacement field as the piecewise smooth solutions containing discontinuities. Then, based on the coarse-grained MD data, a two-phase optimization-based learning approach is proposed to infer the optimal peridynamics model with damage criterion. In the first phase, we identify the optimal nonlocal kernel function from the data sets without material damage to capture the material stiffness properties. Then, in the second phase, the material damage criterion is learnt as a smoothed step function from the data with fractures. As a result, a peridynamics surrogate is obtained. As a continuum model, our peridynamics surrogate model can be employed in further prediction tasks with different grid resolutions from training, and hence allows for substantial reductions in computational cost compared with MD. We illustrate the efficacy of the proposed approach with several numerical tests for the dynamic crack propagation problem in a single-layer graphene. Our tests show that the proposed data-driven model is robust and generalizable, in the sense that it is capable of modeling the initialization and growth of fractures under discretization and loading settings that are different from the ones used during training.

Stress-based topology optimization for fiber composites with improved stiffness and strength: Integrating anisotropic and isotropic materials

Fiber-reinforced materials offer high stiffness- and strength-to-mass ratios to lightweight composite structures. To design stiff, strong, and lightweight fiber-reinforced composite structures, we propose a multimaterial anisotropic stress-constrained topology optimization framework that simultaneously optimizes geometry, distribution of anisotropic (i.e., orthotropic) and isotropic material phases, and local orientations of fiber reinforcements in the anisotropic phase. To achieve high performance in both stiffness and strength, we discover that both isotropic and anisotropic materials are needed: anisotropic materials are preferred in uniaxial members to increase stiffness, while isotropic materials are crucial at multi-axially stressed joints to enhance strength. We introduce multimaterial interpolation schemes to characterize both the stiffness and strength of composites made up of anisotropic and isotropic materials. The characterization of strength is enabled by a novel load factor-based yield function interpolation that consistently integrates anisotropic Tsai–Wu and isotropic von Mises yield criteria. We optimize stress-sensitive domains considering materials with various levels of stiffness and strength anisotropy as well as multiple load cases. The anisotropic stress constraints in the proposed framework effectively inform geometries to reduce stress concentration in fiber composites. The proposed framework provides a rational design paradigm for composite structures, capitalizing on dissimilar stiffness and strength properties of anisotropic and isotropic materials, to potentially benefit various engineering applications.

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.

Design of Asymmetric Parallel Manipulator for Axial-Bending Dynamic Stiffness Analysis

This paper presents an asymmetric 5-bar parallel manipulator capable of characterizing the dynamic stiffness properties of materials used in robotic joints in 2 degrees of freedom, axial and bending, simultaneously. The end effector is actuated by two stepper motors with linear rails. Two force sensors were added to estimate axial force and moment. Experiments were performed in axial compression, bending, and a mixed axial-bending motion. A spring-mass-spring system was constructed to evaluate the fabricated apparatus for frequency analysis up to 20Hz. The frequency analysis result was accurate when compared to the theoretical response of the system. Axial stiffness estimation had an error of 1.5%, bending stiffness had an error of 3.4%, and mixed-mode had a total error of 1.8%. Future experiments will showcase the versatility of the apparatus and test nonlinear samples.

Multiscale optimization of specific elastic properties and microscopic frequency band-gaps of architectured microtruss lattice materials

This paper proposes the development of lattice materials with the concurrent consideration of their specific elastic mechanical properties and their corresponding phononic wave filtering capabilities. A multi-objective and multiscale design optimization problem is presented where the microscopic geometric parameters of truss-like lattice unit cells are introduced as design variables by means of beams cross-section shape transformers. The optimization problem is posed to maximize the stiffness and strength properties of lattice materials along with their frequency band-gap aspect ratios while minimizing their relative density. Floquet-Bloch theorem is employed for the frequency band-gap analysis while the homogenized mechanical properties are estimated using the Cauchy-Born hypothesis and the Hill-Mandel principle of macro-homogeneity. It is found that the band-gap aspect ratios are directly proportional to the macroscopic mechanical properties of the lattice, therefore posing a trade-off design problem. Two case studies are presented for the multi-objective optimization problem including the triangular and the Kagome patched honeycomb topologies. It is demonstrated that the design objectives are satisfied with “I” shaped, horizontally hollow circular or diamond cross-sections. Design charts are introduced which enable the definition of lattice microscopic geometrical attributes required for lattice material development with optimal static macroscopic and dynamic microscopic characteristics.

Rock stiffness measurements fibre Bragg grating sensor (FBGs) and the effect of cyanoacrylate and epoxy resin as adhesive materials

This study investigates the influence of adhesive type and its thickness performance when a highly sensitive Fibre Bragg grating (FBG) sensor is used to determine the stiffness properties of rock and cementitious material. Laboratory uniaxial tests were conducted on limestone and cement-paste specimens, equipped with strain gauges and FBGs attached locally using cyanoacrylate and epoxy-based adhesives. Differences were observed in the FBGs measured strains and the calculated elastic parameters between sensors attached with cyanoacrylate and epoxy-based on the same material (rock and cement). Smaller changes in strain are observed when FBG is attached with cyanoacrylate. Finite Element modelling indicated a reduction in peak strain and increase in Young's modulus from FBG compared to the rock when the adhesive thickness is increased. Also, the strain and stiffness determined vary with the adhesive type. Cyanoacrylate adhesive is relatively more suitable as it gives FBG strain values closer to that of the rock as opposed to Epoxy.

Multiscale characterization and micromechanical modeling of crop stem materials

An essential prerequisite for the efficient biomechanical tailoring of crops is to accurately relate mechanical behavior to compositional and morphological properties across different length scales. In this article, we develop a multiscale approach to predict macroscale stiffness and strength properties of crop stem materials from their hierarchical microstructure. We first discuss the experimental multiscale characterization based on microimaging (micro-CT, light microscopy, transmission electron microscopy) and chemical analysis, with a particular focus on oat stems. We then derive in detail a general micromechanics-based model of macroscale stiffness and strength. We specify our model for oats and validate it against a series of bending experiments that we conducted with oat stem samples. In the context of biomechanical tailoring, we demonstrate that our model can predict the effects of genetic modifications of microscale composition and morphology on macroscale mechanical properties of thale cress that is available in the literature.

Analysis of influence of cold plasma on stiffness properties of polymeric materials

A model of the polyester fabric behavior subjected to plasma treatment with a reduced pressure is proposed to evaluate its deformability in its plane. The method for identifying stiffness properties is described, and the results of processing the full-scale experiments as well as the results of the numerical studies of the problem regarding stretching samples of the fabric are presented. For the numerical analysis of the deformation process of the fabric samples the finite element method was used. The proposed finite-element model of deformation of nonlinear elastic fabric materials allows us to study the patterns of behavior of the tissue samples under various loads, given that the material is not able to support the compressive loads. The developed technique for an experimental determination of the stiffness characteristics of fabrics according to the results of testing the samples, cut at different angles to the base, under various stretching forces, made it possible to analyze the influence of treatment of the fabric with a cold plasma on its mechanical characteristics.

Recent developments in semi-active control of magnetorheological materials-based sandwich structures: A review

Magnetorheological (MR) materials are kinds of smart materials whose rheological characteristics are controllable with the application of external magnetic fields. In the last few decades, MR materials are well established as one of the leading smart materials for use in adaptive sandwich structures and systems for salient vibration control. This article reviews the semi-active vibration suppression of flexible structures with smart materials of MR fluids (MRFs) and MR elastomers (MREs). Stiffness and damping characteristics of beams, plates, panels, and shells integrating the core layer of MRFs and MREs are discussed in terms of field-dependent controllability. To keep the integrity of the knowledge, this review includes a study on free and forced vibration characteristics of sandwich structures with fully and various configurations of partial MR treatments, stability analysis of MR sandwich structures under rotating conditions and developments in identifying the optimal locations of MR sandwich structures for better vibration control are also discussed. Further, this article focuses on the role of carbon nanotubes in enhancing the field-dependent stiffness and damping properties of MR materials. A few of the most relevant research articles are reviewed and presented here briefly.

Effects of material properties on the mobility of granular flow

In this study, we investigate the influence of material properties on the mobility of granular flow through granular column collapse experiments using the Smooth Particle Hydrodynamics method and a continuum constitutive model capable of describing the nonlinear responses of granular materials. Numerical simulations are systematically compared with available experimental data and well-established empirical laws to validate the capability of this numerical approach for simulating the dynamics of granular flow. Based on this validation, a series of numerical experiments is conducted to investigate the effects of strength properties (i.e. friction and dilation), density and stiffness properties (i.e. Young’s modulus and Poisson’s ratio) on the run-out distance and energy evolution of granular flows, which were unclear or contradictorily reported in previous experimental studies. We found that as the friction angle increases, the material is less mobilised and hence the run-out distance is shorter. In addition, a denser state (i.e. more dilation) facilitates its mobilisation associated with a greater volume expansion during the collapse. The density and stiffness properties of granular materials, nonetheless, have negligible effects on the deposit morphology and run-out distance of granular flow. To further quantify the effects of material properties, the run-out scaling law of granular flow, which describes the relationship between the run-out distance and the initial geometry of granular columns, is analysed and shown to be significantly influenced by the friction and dilation of the materials.

Experimental assessment of stiffness and energy dissipation properties of disk-shaped polymer-based composite specimens by in-plane torsion testing

Torsion testing machines are widely used either to measure the strength, stiffness and stress-strain properties of materials or to replicate real-life service conditions. In this paper, a novel experimental method is presented, based on the development of a dedicated steel structure to be used in conjunction with a universal testing machine. This equipment allows applying cyclic in-plane torsion loads on disk-shaped components. The proposed approach aims to enable the assessment of stiffness and damping properties on specimens enabling the application of higher loads in comparison with the traditional machines.Specifically, dynamic trials were performed by attaching the composite specimens and the steel structure to the testing machine, such that the uniaxial controlled displacements can be used to exert the desired cyclic loads onto the specimen. Both torsional stiffness and energy loss were measured from the steady-state load-displacement hysteresis cycles. Amplitudes of sine signals, from 0.05 to 0.2 mm, and a frequency ranging between 1 and 20 Hz, were used in the experiments. The results are presented comparing the behaviour of two polymer matrix composites, with the same number of identical laminae, but characterized by different stacking sequences, namely unidirectional and quasi-isotropic configurations.

Quantifying the Tensile Properties of Hevea brasiliensis – Silicone Biocomposite using Neo – Hookean Model

Incorporation of natural fibers into composites have been continuously researched in moving towards a greener environment. As environmental issues such as climate change and global warming is becoming severe, green technology is one of the ways to reduce it. Hevea brasiliensis or commonly called rubber tree produced a lot of sawdust during the conversion of the raw material into product. The sawdust is known as an agricultural waste which has no economic value. Therefore, this study for the first time attempts to utilize the Hevea brasiliensis sawdust by incorporating it with silicone rubber in the making of a new biocomposite material. The samples were prepared in two weight compositions, 0 wt% and 16 wt% in accordance to ASTM D412. Tensile properties of biocomposite was then determined using 3382 Universal Testing Machine 100kN (Instron, U.S.A., 2008). Neo Hookean hyperelastic model was employed where the material constant, C1 values were obtained. The graph plotted shows that the hyperelastic model used can mimic the deformation behavior of silicone biocomposites. The material constants are observed to increase as Hevea brasiliensis fiber are introduced into it. Hence, it can be concluded that pure silicone rubber has higher tensile strength compared to 16 wt% hevea brasiliensis – silicone biocomposite and the addition of fiber increase the stiffness properties of material produced.

Sensing of Damage and Repair of Cement Mortar Using Electromechanical Impedance.

Lead zirconium titanate (PZT) has recently emerged as a low-cost material for non-destructive monitoring for civil structures. Despite the numerous studies employing PZT transducers for structural health monitoring, no studies have assessed the effects of both damage and repair on the electromechanical impedance response in cementitious materials. To this end, this study was conducted to assess the effects of the damage and repair of mortar samples on the electromechanical response of a surface-mounted PZT transducer. When damage was introduced to the specimen in stages, the resonance frequencies of the admittance signature were shifted to lower frequencies as the damage increased, and an increase in the peak amplitude was detected, indicating an increase in the damping and a reduction in the material stiffness properties. Also, increasing the damage in the material has been shown to decrease the sensitivity of the PZT to further damage. During the repair process, a noticeable difference between the after-damage and the after-repair admittance signatures was noted. The root-mean-square deviation (RMSD) showed a decreasing trend during the repair process, when compared to the before repair RMSD response which indicated a partial recovery for the material properties by decreasing the damping property in the material.

Coupled Thermal-Mechanical Progressive Damage Model with Strain and Heating Rate Effects for Lightning Strike Damage Assessment

This paper proposes a progressive damage model incorporating strain and heating rate effects for the prediction of composite specimen damage resulting from simulated lightning strike test conditions. A mature and robust customised failure model has been developed. The method used a scaling factor approach and non-linear degradation models from published works to modify the material moduli, strength and stiffness properties to reflect the effects of combined strain and thermal loading. Hashin/Puck failure criteria was used prior to progressive damage modelling of the material. Each component of the method was benchmarked against appropriate literature. A three stage modelling framework was demonstrated where an initial plasma model predicts specimen surface loads (electrical, thermal, pressure); a coupled thermal-electric model predicts specimen temperature resulting from the electrical load; and a third, dynamic, coupled temperature-displacement, explicit model predicts the material state due to the thermal load, the resulting thermal-expansion and the lightning plasma applied pressure loading. Unprotected specimen damage results were presented for two SAE lightning test Waveforms (B & A); with the results illustrating how thermal and mechanical damage behaviour varied with waveform duration and peak current.

Fiber Optic Shape Sensing for Soft Robotics.

While soft material actuators can undergo large deformations to execute very complex motions, what is critically lacking in soft material robotic systems is the ability to collect high-resolution shape information for sophisticated functions such as environmental mapping, collision detection, and full state feedback control. This work explores the potential of a nearly commercial fiber optic shape sensor (FOSS) and presents the first demonstrations of a monolithic, multicore FOSS integrated into the structure of a fiber-reinforced soft actuator. In this pilot study, we report an open loop sensorized soft actuator capable of submillimeter position feedback that can detect the soft actuator's shape, environmental shapes, collision locations, and material stiffness properties.

Triaxial extension and tension tests on lime-cement-improved clay

This paper presents the results of a series of undrained and drained isotropic consolidated triaxial extension, tension and compression laboratory tests on lime-cement-improved very soft clay. The main objective of these tests was to investigate the material strength and stiffness properties for stress conditions similar to those expected on the passive side of excavations where a retaining structure is supported by Deep Mixing columns. The different stress paths to failure were obtained by varying the directions of the major and minor principal stresses in a conventional triaxial test cell. The undrained tests conducted at low consolidation stresses, corresponding to depths of approximately 0–10 m below the ground surface, revealed significant differences in undrained strength depending on the directions of the major and minor principal stresses, indicating anisotropic material behavior. Based on the undrained triaxial test results, the relationship among the undrained strength, the effective consolidation stress and the over-consolidation ratio (OCR) is presented for different stress paths to failure.The experimental data from the drained tests show that a failure surface comprised of a shear failure function based on the Mohr-Coulomb failure criterion and a tensile failure function based on the tensile strength and the confining stress can be applied for lime-cement-stabilized clay.

Microimaging-informed continuum micromechanics accurately predicts macroscopic stiffness and strength properties of hierarchical plant culm materials

Plant materials exhibit a wide range of highly anisotropic mechanical behavior due to a hierarchy of microheterogeneous structures at different length scales. In this article, we present a micromechanics approach that derives a hierarchical microstructure driven model of macroscopic stiffness and strength properties of anisotropic culm materials. As model input, it requires mechanical properties of the base constituents such as cellulose and lignin as well as morphology and volume fractions of all heterogeneous components at each hierarchical level. The latter can be retrieved from imaging data at different length scales, obtained from scanning electron and transmission electron microscopy. We illustrate our modeling approach for the example of bamboo that has gained increasing attention in the last decade due to its role as a sustainable building material. Validating its predictions of macroscopic stiffness moduli and ultimate strength with corresponding experimental measurements, we demonstrate that the micromechanics model provides excellent accuracy without any further phenomenological calibration. We also show that the multiscale modeling approach enables a better physics-based understanding of the origins of bamboo stiffness and strength across different scales.

Experimental study of the influence of preliminary complex mechanical loads on the deformation and strength properties of polymer composites

The paper discusses the issues of complex cyclic and low-speed impact loads on the strength and deformation properties of polymer composites. The results of experimental study of the influence of preliminary cyclic loads on the residual properties of samples of layered-fibrous composite materials under various layouts and loading modes are presented. Experiments were carried out using the research facilities of the Center for Experimental Mechanics (http://www.ckp-rf.ru/ckp/353547/). As part of the work, a series of tests was performed on fiberglass composite samples made with three types of laying the reinforcement layers [0/90], [±45], [0/30/0/60]. For each type of samples static strength and stiffness properties were determined. Fatigue tests were performed at the same level of maximum stress in the cycle, frequency and asymmetry coefficient. The dependences of the change in the residual strength properties of layered fibrous composites are presented in the form of fatigue sensitivity diagrams. For samples with layouts [0/90], [0/30/0/60], a staging change in relative residual static strength was noted. For the studies materials, areas of initial fatigue sensitivity, stabilization and exacerbation of fatigue sensitivity were revealed. The research of the regularities of changes in stiffness and strength properties of polymer composite materials (PCM) in the process of fatigue accumulation of damage at various stress levels of cyclic loads was conducted for samples with reinforcement angles [0/90]. The test results are presented in the form of diagrams of changes in the residual strength and stiffness properties of fiberglass samples. For the fiberglass specimens, in this range of loads, the dependences were non-linear and had a similar pattern of change. The results of the study of the influence of preliminary low-velocity impact of varying intensity on the residual mechanical characteristics of the sample plates of carbon-fiber composite materials with spatial reinforcement schemes are presented. As a result, it was noted that the additional preliminary shock reduces the residual strength, however, when failure, the stage of postcritical deformation is realized.

Primary yielding locus of cement-stabilized marine clay and its applications

ABSTRACTStrength and stiffness properties of materials are widely studied and used in civil engineering practice. However, most studies are based on unconfined conditions, which are different from real status of soil. This study investigated the primary yielding and yield locus for cement-stabilized marine clay. In this study, two types of cement-stabilized soils were studied through isotropic compression, triaxial drained shearing, unconfined compression, and bender element testing. Specimens with 20–50% of cement content and 7–90 days of curing period were used for the tests. Stress–strain behavior and primary yielding were evaluated, followed by construction of the primary yield locus. The characteristics of the primary yield locus and its development with curing time then were studied. The results showed that the properties of the primary yield locus were dependent on the type of stabilized soil, but were independent of the cement content and curing period. Thus, the approach provides a way to estimate the primary yield stress and drained stress path before primary yielding for cement-stabilized soil under confined condition. An empirical function was used to fit the primary yield locus. The primary isotropic yield stress was correlated to unconfined compressive strength or maximum shear modulus. Three indirect methods were proposed to predict the primary yield stress for cement-stabilized marine clay. The results showed that the primary yield stress can be estimated with reasonable accuracy.