Large Deformation Range Research Articles

A semi-analytical model for predicting nonlinear tensile behaviour of corrugated flexible composite skin

This paper seeks to present a semi-analytical model for predicting the nonlinear tensile properties of corrugated flexible composite skin (FCS) within large deformation range based on iterative integration procedure. The FCS is constructed with two thin-walled curved fibre-reinforced-plastics (FRP) composite shells with a biaxially symmetrical lenticular cross-section, which can be stretched largely along the corrugated direction through pure elastic deformation. Analytical formulations for tensile stiffness of the FCS are derived based on the unit virtual load method, and geometrical equations are established to describe tensile deformation of the FCS. By means of linear elastic and strain energy theory, new geometry and tensile force increment of extended FCS are calculated at a given small increment of tensile displacement. In order to obtain the tensile behaviour of the FCS within large deformation range, semi-analytical model is presented by using the iterative calculation, and then is verified from experiments. Finally, the effect of the geometry on tensile behaviour of the FCS is analyzed numerically.

High strain rate response of bio-composites using split Hopkinson pressure bar and digital image correlation technique

ABSTRACTIn this research, high strain rate response and energy absorption characteristics under dynamic compression loading of five different bio-composites were studied using a compression split Hopkinson pressure bar (SHPB) and DIC (digital image correlation) technique. This study is to map suitability of plant-based materials instead of petroleum-based plastic as a constituent raw material in composites. Bio-composites panels were made from Southern yellow pine (SYP), Corn starch (CS), and Methylene diphenyl diisocyanate (MDI) using a Dieffenbacher hot press. The ability of non-contact DIC analysis served as a valuable tool to measure the strains over a large range of deformation in wood-based bio-composites subjected to high strain rate compressive loading. Among all, Material 2 bio-composite with high manufacturing pressure had highest peak strength, shows that material behaviour at high strain rates is strongly dependent on the manufacturing pressure during fabrication. Presence of corn starch marginally increased the energy absorption capacity.

Modeling and Verification of a New Hyperelastic Model for Rubber‐Like Materials

The essential evaluation criterion for the hyperelastic model is its ability to describe the mechanical behavior of rubber‐like materials under different deformation modes over a large deformation range accurately. Based on the Seth strain tensor invariant, a new hyperelastic model for isotropic and incompressible rubber‐like materials is proposed. In order to investigate the prediction ability of the new model, the parameters of the new model, the Yeoh model, and the Carroll model are identified by test data of 8% vulcanized rubber and two different types of carbon black filled rubber, respectively. To this end, the data of uniaxial tension and equibiaxial tension are used simultaneously. Then, the same set of model parameters is used for prediction of pure shear (plane tension) deformation. The results show that the new model not only can predict the test data of pure shear (or plane tension) accurately, but also can be reliable to describe the response of various rubber materials over a large deformation range. Finally, the finite element simulation and experiment on static stiffness of rubber bushing are carried out based on the new model. By comparison of the experimental data with the simulation data, the new model can accurately reflect the mechanical behavior of rubber bushing. The new model can be used for performance analysis of rubber products and has better application value.

Critical Phenomena in Portevin–Le Chatelier effect during compression of aluminium-magnesium alloy and stored energy evolution

This work was inspired by works of Gianfranco D’Anna (2000) where the Portevin-Le Chaˆtelier effect (PLC) was investigated by compressing Al-Mg alloy specimen in a very large deformation range and the results were interpreted from the viewpoint of phase transitions and critical phenomena. Two critical points where deformation process changes from “laminar” to jerky flow and back were noticed. We found that the second critical point where the rate of the serrations is decreased before the macroscopic fracture is not reachable for some alloys even with proposed geometry. We have tested 2 sets of specimens made of the same AMG6 alloy (~6% of magnesium) but with different amount of Si obtained from different producers. Specimens with a higher amount of Si tends to fracture before reaching the second point.Also, we have measured the amount of stored energy which can be recovered as heat during the annealing process. We used the differential scanning calorimeter STA "Jupiter" 449. We found that the amount of this energy sharply increases with the beginning of PLC serrations (first critical point) and drops at a second critical point or at macroscopic fracture. This can be related to a special type of critical phenomena—structural scaling transitions in mesodefect ensembles and associated structural relaxation mechanisms Naimark (2016)

Numerical and experimental investigation of an elastoplastic contact model for spherical discrete elements

A contact model for the normal interaction between elastoplastic spherical discrete elements has been investigated in the present paper. The Walton–Braun model with linear loading and unloading has been revisited. The main objectives of the research have been to validate the applicability of the linear loading and unloading models and estimate the loading and unloading stiffness parameters. The investigation has combined experimental tests and finite element simulations. Both experimental and numerical results have proved that the interaction between the spheres subjected to a contact pressure inducing a plastic deformation can be approximated by a linear relationship in quite a large range of elastoplastic deformation. Similarly, the linear model has been shown to be suitable for the unloading. It has been demonstrated that the Storåkers model provides a good evaluation of the loading stiffness for the elastoplastic contact and the unloading stiffness can be assumed as varying linearly with the deformation of the contacting spheres. The unloading stiffness can be expressed in a convenient way as a function of the Young’s modulus and certain scaling factor dependent on the dimensionless parameter defining the level of the sphere deformation.

Irreversible hardening of a colloidal gel under shear: The smart response of natural rubber latex gels

Natural rubber is obtained by processing natural rubber latex, a liquid colloidal suspension that rapidly gels after exudation from the tree. We prepared such gels by acidification, in a large range of particle volume fractions, and investigated their rheological properties. We show that natural rubber latex gels exhibit a unique behavior of irreversible strain hardening: when subjected to a large enough strain, the elastic modulus increases irreversibly. Hardening proceeds over a large range of deformations in such a way that the material maintains an elastic modulus close to, or slightly higher than the imposed shear stress. Local displacements inside the gel are investigated by ultrasound imaging coupled to oscillatory rheometry, together with a Fourier decomposition of the oscillatory response of the material during hardening. Our observations suggest that hardening is associated with irreversible local rearrangements of the fractal structure, which occur homogeneously throughout the sample.

Investigations in the field of material mechanics using strain gages

AbstractIn this contribution, investigations of the stress‐strain behavior of different metals using strain gage technique are presented. The measurement of strains using strain gages provides high measuring accuracy. In case of large deformations, the nonlinearity of the resistance‐strain‐relation, including elastic and plastic strain of the gage grid material, has to be considered. Moreover, for the detection of large deformations, high‐elongation strain gages and special bonding adhesives are used. Furthermore, at larger resistance changes the nonlinearity of the Wheatstone bridge has to be taken into account. As an example, the stress‐strain behavior of the steel 50CrV4 with 3 different process states in the small deformation range during tensile tests is demonstrated. The differences of the resulting stress‐strain curves of the material in the different process states are analyzed. Additionally, specimens of the aluminum alloy EN AW‐2024 are investigated in a large deformation range using tensile tests. Therein, the strain transmission enabled by the bonding is in the special focus. Furthermore, results of the large deformation tests are compared to the strain measurement using Digital Image Correlation.

Effects of different steel-concrete composite slabs on rigid steel beam-column connection under a column removal scenario

Trapezoidal and Reentrant are two ordinary deck profiles in modern steel-concrete composite floor system in China. The progressive collapse resistance of rigid steel beam-column connections with these two different composite deck profiles was experimentally investigated. This research addressed progressive collapse behavior of components evaluated by removing columns through the alternate load path method where the connections simulated the behavior of connections from a multi-bay steel moment-resisting frame. Also, collapse resistance of the connection above the removed column and the adjacent connection was considered. The results were compared with a bare steel subassembly, which has the same configuration but without composite slab, the load carrying capacity of the specimen with trapezoidal steel deck is improved by 28% and the specimen with reentrant steel deck is improved by 44%. The type of steel decks influenced the degree of restraint to the beam top flange and resistance of the connection. The specimen with trapezoidal steel deck had a higher plastic rotation capacity than the reentrant one, but the specimen with reentrant steel deck had improved composite behavior in the large deformation range and, therefore, developed more catenary action than the specimens with trapezoidal steel deck. Overall, the specimens with reentrant steel deck had a better performance under the progressive collapse situation, however, some constructional measures must be made to delay the bottom beam flange fracture.

An alternative procedure to identify stress-strain relation for DP980 sheet over a large strain range

In sheet metal forming, the standard uniaxial tensile test is a well-established testing method used to achieve stress-strain relation or flow curve for examined material. In agreement with the development of material science, the number of forming processes that exceeded the maximum uniform strain observed in a uniaxial tensile test is myriad. To obtain the relationship between stresses and strains over a large range of deformation, extrapolation of a common hardening model (Swift model or Voce model) is only accepted for some specific materials. Therefore, expensive calibrating methods, such as inverse finite element analysis and virtual field method, are widely used to identify the flow curve for recently developed sheet materials, for example, advanced high strength steels or aluminium alloys. This study presents an alternative procedure to identify the flow curve for sheet metals by using the extrapolation method. Key to the success of this procedure is using the Kim-Tuan hardening model, a newly developed hardening model proposed by the authors. The examined material is DP980 sheet that is tested material in Benchmark 01 of the NUMISHEET 2018 conference. To verify the accuracy of the calibrated flow curve, this curve is imported into a finite element analysis for a uniaxial tensile specimen and computational loading forces according to gauge length displacement are compared with experimental observation supported from the Benchmark’s data.

Enhancing the deformation range of ionic polymer metal composites through electrostatic actuation

The large range of deformations of ionic polymer metal composites (IPMCs) has often been proposed as a key advantage of these soft active materials. Nevertheless, many applications in soft robotics still cannot be addressed by current IPMC technology, demanding an even wider deformation range. Here, we empirically demonstrate the feasibility of integrating electrostatic actuation to enhance IPMC deformations. Through the use of external contactless electrodes, an electrostatic pressure is generated on the IPMC, thereby magnifying the deformation elicited by the small voltage applied across its electrodes. A mathematical model is established to predict the onset of the pull-in instability, which defines when electrostatic actuation can be effectively utilized to enhance IPMC performance.

Mesoscopic friction and network morphology control the mechanics and processing of carbon nanotube yarns

Carbon nanotube (CNT) yarns are synthetic nanomaterials of interest for diverse applications. To bring fundamental understanding into the yarn formation process, we perform mesoscopic scale distinct element method (mDEM) simulations for the stretching of CNT networks. The parameters used by mDEM, including the mesoscale friction, are based on full atomistic results. By bridging across the atomistic and mesoscopic length scales, our model predicts accurately the mechanical response of the network over a large deformation range. At small and moderate deformations, the microstructural evolution is dominated by zipping relaxations directed along the applied strain direction. At larger deformations, the occurrence of energetic elasticity promotes yarn densification, by lowering CNT waviness and eliminating squashed pores. Next, by varying the mesoscopic dissipation as well as the network structure, we reveal that the mesoscale friction and film morphology are key factors for the yarn formation: While lack of friction compromises the strain-induced alignment process, phononic and polymeric friction promote CNT alignment by enabling load transfer and directed zipping relaxations, especially in networks containing long and entangled CNTs. Yarns drawn from cellular networks are shown instead to maintain high porosity, even with enhanced polymeric friction.

Compliant four-bar linkage synthesis with second-order flexure hinge approximation

The paper discusses an original methodology for addressing the synthesis of a compliant four-bar mechanism for prescribed finite coupler motion. The proposed method is based on the modelling of the four flexure hinges by using a planetary arrangement (two external cylinders rolling without slipping one on the other) able to accurately reproduce the relative motion between connected parts for a large range of deformation. The adopted approach allows a trade-off between accuracy and limited complexity in deducing the closure loop equations of the whole mechanism. The methodology is applied on a test case of a four-bar compliant linkage whose coupler occupies a prescribed set of finitely separated positions. The synthesized linkage has been analysed both with a pseudo-rigid model (built with mid-sized hinges) and a nonlinear finite element model.

Reduction of Dynamic Impacts in Block Made of Concrete - Rubber Composites

Abstract The paper presents numerical analysis of block made of three layers: concrete with I-shape rubber pads, space filled with air and concrete with embedded cross rubber pads, respectively. The block is subjected to the dynamic load. To the analysis as rubber the hyperelastic incompressible Zahorski material model was assumed. This material well describes the real material properties in the range of large elastic deformations. Embedded rubber pads provide an additional protection against the transversal dynamic load. ADINA software was utilized to perform numerical analysis of determining the percentage damping factor of rubber-concrete composite in comparison with block made of concrete.

Triple shape memory polymers by 4D printing

This article aims at introducing triple shape memory polymers (SMPs) by four-dimensional (4D) printing technology and shaping adaptive structures for mechanical/bio-medical devices. The main approach is based on arranging hot–cold programming of SMPs with fused decomposition modeling technology to engineer adaptive structures with triple shape memory effect (SME). Experiments are conducted to characterize elasto-plastic and hyper-elastic thermo-mechanical material properties of SMPs in low and high temperatures at large deformation regime. The feasibility of the dual and triple SMPs with self-bending features is demonstrated experimentally. It is advantageous in situations either where it is desired to perform mechanical manipulations on the 4D printed objects for specific purposes or when they experience cold programming inevitably before activation. A phenomenological 3D constitutive model is developed for quantitative understanding of dual/triple SME of SMPs fabricated by 4D printing in the large deformation range. Governing equations of equilibrium are established for adaptive structures on the basis of the nonlinear Green–Lagrange strains. They are then solved by developing a finite element approach along with an elastic-predictor plastic-corrector return map procedure accomplished by the Newton–Raphson method. The computational tool is applied to simulate dual/triple SMP structures enabled by 4D printing and explore hot–cold programming mechanisms behind material tailoring. It is shown that the 4D printed dual/triple SMPs have great potential in mechanical/bio-medical applications such as self-bending gripers/stents and self-shrinking/tightening staples.

Control of Oxidation and Spin State in a Single-Molecule Junction.

The oxidation and spin state of a metal-organic molecule determine its chemical reactivity and magnetic properties. Here, we demonstrate the reversible control of the oxidation and spin state in a single Fe porphyrin molecule in the force field of the tip of a scanning tunneling microscope. Within the regimes of half-integer and integer spin state, we can further track the evolution of the magnetocrystalline anisotropy. Our experimental results are corroborated by density functional theory and wave function theory. This combined analysis allows us to draw a complete picture of the molecular states over a large range of intramolecular deformations.

A Nonlinear Viscoelastic Model for Adipose Tissue Representing Tissue Response at a Wide Range of Strain Rates and High Strain Levels.

Finite element human body models (FEHBMs) are nowadays commonly used to simulate pre- and in-crash occupant response in order to develop advanced safety systems. In this study, a biofidelic model for adipose tissue is developed for this application. It is a nonlinear viscoelastic model based on the Reese et al.'s formulation. The model is formulated in a large strain framework and applied for finite element (FE) simulation of two types of experiments: rheological experiments and ramped-displacement experiments. The adipose tissue behavior in both experiments is represented well by this model. It indicates the capability of the model to be used in large deformation and wide range of strain rates for application in human body models.

DESIGN OPTIMIZATION OF C-SHAPED SUPERELASTIC SMA SHEET WITH CONSTANT FORCE

Constant force component is very useful in medical device, such as forceps with constant force, which may prevent soft tissues from injures due to overloading. This paper studied the optimization procedure in constant force component for superelastic shape memory alloy, and tried to find the rule of obtaining constant force within a relatively large deformation range for superelastic C-shaped shape memory alloy sheet. The optimization concept of combing finite element analysis in ANSYS with genetic algorithm in MATLAB was presented for designing constant force component using superelastic SMA. The computational optimization and experimental results of the C-shaped shape memory alloy sheet showed that the proposed optimization method was potential for superelastic shape memory alloy. The optimization results were consistent with the experimental results. It was demonstrated that constant force could be obtained within a relatively large deformation range by varying the initial shape of the superelastic SMA component.

A flexible piezoresistive carbon black network in silicone rubber for wide range deformation and strain sensing

This work presents the design, fabrication, and measurement of a piezoresistive device with a carbon black (CB) particle network in a highly flexible silicone rubber for large deformation and wide range strain sensing. The piezoresistive composite film was fabricated with a mixture of silicone rubber and CB filler particles. The test results showed that the CB particle network in the silicone rubber strongly affected the resistance of the device during the process of drawing and its recovery. We found that the 50% volume ratio of CB filler particles showed a lower relative resistance than the 33.3% volume ratio of CB filler particles, but with an advantage of good resistance recovery stability and a smaller perturbation error (smaller changed resistance) during the periodic back and forth linear motor test. With both having a 50% volume ratio of CB filler particles and a 33.3% volume ratio of CB filler particles, one can reach up to 200% strain with resistances 18 kΩ and 110 kΩ, respectively. We also found that the relative resistance increased in an approximately linear relationship corresponding to the value of step-increased instantaneous length for the reported device. Moreover, an application test through hand drawing was used to demonstrate the piezoresistive performance of the device, which showed that the reported device was capable of measuring the instantaneous length with large deformation.

The translational force acting on an elastic filament confined in a fluid-filled channel of varying width

A phenomenon that is exploited in material processing and also arises naturally in material systems is the confinement of a flexible elastic filament within a long, hollow tube and the potential transport of that filament along the length of the tube. The objective of the present paper is to describe the general nature of that confinement and to propose a physical model which can serve as a basis for extracting a quantitative estimate of the magnitude of a driving force for translation of the filament along the length of the confining tube. The focus is on fluctuations of a single filament confined to a planar motion within a tapered channel, including the prospect of fluctuations into the range of large deformation.

Effect of nodal mass on macroscopic mechanical properties of nanoporous metals

The current work investigates the effect of the nodal mass on the macroscopic mechanical behavior of nanoporous metals using the Finite Element Method. A nodal corrected beam modeling concept is introduced that allows local incorporation of the effective elastoplastic mechanical behavior of the nodal mass in the nodal area of a representative volume element (RVE). The calibration to the corresponding Finite Element solid model is achieved by integrating additional geometry and material parameters to the so-called nodal areas in the beam model. With this technique an excellent prediction can be achieved over a large range of deformation for different types of RVEs. From the results of the nodal corrected beam model, modified leading constants are determined in the scaling laws for Young's modulus and yield strength. The effect of the nodal correction is also studied with respect to various randomization levels. Finally, the ligament size dependent strength is analyzed by applying the proposed model to experimental data. It could be shown that the nodal correction improves the overall agreement with literature data, particularly for such data points that are related to samples with a high solid fraction.