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In this paper, a three-dimensional anisotropic multi-surface model for the in-plane elastoplastic deformation of paper and paperboard is developed. The model is based on the concept of structural tensors. It employs three different yield functions and parameterised consistency conditions for three different loading scenarios. The evolution of the yield surface with plastic strain is described by multiple hardening variables. Furthermore, the evolution equations are integrated using the unconditionally stable backward Euler method. Also, the internal variables are updated using a particular form of the elastic predictor/plastic corrector algorithm. The constitutive model is calibrated from a set of simple uniaxial tension tests performed in various directions of the material and is validated against loading in other directions. Additionally, the predictive capability as well as the numerical performance of the constitutive model is accessed against an existing non-quadratic plasticity model. Finally, the applicability of the constitutive model is demonstrated by performing a tensile test on a paperboard with a hole. [ABSTRACT FROM AUTHOR]

The problem of failure in the facings of a corrugated board is investigated by means of a mechanical model utilizing the principles of continuum damage mechanics. To evaluate the predictive capability of the model, experiments have been conducted on in-plane isotropic single and two-ply paper sheets manufactured in the laboratory. It is found that there is a qualitative agreement between model and experiments. The model can predict if delamination will occur before the top-ply loses its in-plane load carrying capacity due to material degradation. To circumvent delamination problems, a material with low stiffness should be used in the top-ply (as compared to the bottom-ply) and a very thin top-ply should be avoided. It is exemplified that it is possible to steer the failure mode by optimizing the degree of beating or the ply thickness. It is demonstrated that plasticity may be omitted in the analysis if one is only interested in characterizing the expected type of failure mode. An important key result is that, if the circumstances are that severe damage growth takes place in the crack-tip region, then delamination most likely occur which may be in contradiction to what is anticipated from classical theories of fracture mechanics. [ABSTRACT FROM AUTHOR]

For research on the effect of different working loads on the deformation of variable base circle radius scroll expander scroll teeth, a multi-field-coupled calculation method is proposed to reveal the deformation law of scroll teeth under different working loads. In this paper, the equations of the variable base radius profile are derived using the normal isometric method to establish a three-dimensional model of the variable base radius scroll expander. The CFD dynamic mesh technique is used to simulate the working process of a variable base radius scroll expander to obtain the flow field variation in the inner part of the working chamber. The results of the simulation are applied to the scroll teeth by interpolation to analyze the deformation of the scroll under single-field loading and multi-field coupling, to obtain the deformation law of the scroll teeth. The results of the study show that the deformation of the scroll teeth does not decrease linearly with the involute spreading angle from the head to the tail of the teeth due to the uneven temperature distribution of the scroll expander. The thermal stress of the temperature load impacts the deformation trend and amount of the scroll tooth, whereas the gas force load just modifies the amount of scroll tooth deformation and has a lower effect on the scroll tooth's deformation trend. Under different loads, the same deformation and different deformation on the scroll teeth can interact with each other to reduce the scroll tooth deformation to a certain extent. [ABSTRACT FROM AUTHOR]

The dynamic mechanical response and deformation mechanism of poly (ε-caprolactone) (PCL) and epoxy resins shape memory polymer (SMP) composites were investigated in this paper. The SMP composites were a blend of PCL and epoxy resins by using the facile melt-mixing method. The distribution of PCL in the composites was observed by SEM, which was in from microparticle morphology to continuous morphology with the increasing PCL content. And the dynamic mechanical analyzer (DMA) tests were performed to demonstrate the viscoelastic properties and shape memory effect of the PCL/EP composites. Based on the above characterization of PCL/EP composites, the split Hopkinson pressure bar (SHPB) tests were performed to study the dynamic mechanical properties at the strain rates of 4000/s to 7000/s. The results showed that the flow stress increased with the increasing strain rate, which exhibited an obvious sensitivity to strain rate. However, the flow stress of PCL/EP decreases with the increasing PCL content due to the low strength of PCL. And PCL/EP composites failed in a typical ductile failure mode under quasi-static loading, whereas an excellent plastic deformation ability was observed at high strain rates, which was attributed to the heat generated by the plastic work during the adiabatic compression. Combining with the experimental results, the corresponding deformation mechanism was also discussed. [ABSTRACT FROM AUTHOR]

The contact between the tire and the road surface causes tread deformation, and using traditional methods to measure tire tread deformation is difficult and time-consuming. Therefore, based on the principle of the digital image correlation method, this paper develops a binocular vision measurement system and realizes the measurement of tire tread deformation through the test bench for tire ground pressure distribution measurement. The related programs of the measurement system, including camera calibration, image matching, and strain fitting, are proposed. The deformation measurement accuracy of the test bench is validated by the sprayed speckle rubber sheet test, and the relative error of the theoretical value and measurement value is within 2%. The tire tread deformation test under static loading conditions was carried out using the test bench, and the tread strain distribution in the contact area was obtained. The analysis of the test results shows that the strain distribution in the contact patch is axisymmetric under static loading conditions. The longitudinal (tire rolling direction) deformation of the tread at the leading edge and the trailing edge area of the contact patch has the largest strain, while the deformation of the shoulder area on both sides of the contact patch is relatively small. For lateral (tire axial direction) deformation, the leading edge and the trailing edge areas of the contact patch are less deformed, and the strain distribution is approximately axisymmetric. The shoulder area of the contact surface has a larger deformation. The tire's outer shoulder area has a larger deformation than the inside shoulder area, which may be due to the asymmetric tread structure of the tire. For the vertical deformation of the tread, the central area of the tread has the smallest strain, while the surrounding area has a much larger vertical strain. [ABSTRACT FROM AUTHOR]

Soft robots have been investigated for various applications due to their inherently superior deformability and flexibility compared to rigid-link robots. However, these robots struggle to perform tasks that require on-demand stiffness, that is, exerting sufficient forces within allowable deflection. In addition, the soft and compliant materials also introduce large deformation and non-negligible nonlinearity, which makes the stiffness analysis and modelling of soft robots fundamentally challenging. This paper proposes a modelling framework to investigate the underlying stiffness and the equivalent compliance properties of soft robots under different configurations. Firstly, a modelling and analysis methodology is described based on Lie theory. Here, we derive two sets (the piecewise constant curvature and Cosserat rod model) of compliance models. Furthermore, the methodology can accommodate the nonlinear responses (e.g., bending angles) resulting from elongation of robots. Using this proposed methodology, the general Cartesian stiffness or compliance matrix can be derived and used for configuration-dependent stiffness analysis. The proposed framework is then instantiated and implemented on fluidic-driven soft continuum robots. The efficacy and modelling accuracy of the proposed methodology are validated using both simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study on the forming mechanism and bearing behavior of single-lap composite riveted joints with different hole diameters (4.82 mm and 4.9 mm) and squeeze forces (15 KN, 18 KN, 20 KN, and 23 KN). Pressure riveting and tensile tests are conducted to composite riveted joints to obtain the joint interference, joint stiffness and bearing strength needed to quantitatively evaluate their deformation features and mechanical properties. Furthermore, microscopic studies on damaged areas using applying ultra-depth three-dimensional microscope to monitor damage evolution are conducted to comprehend the joint shear failure mechanism. Results show that the hole diameter and riveting force have a significant effect on the performance of the joint. The forming damage occurs mainly in the hole wall near the driven head and is dominated by fiber crushing and interfacial shear cracks. The radial expansion of the rivet shank is not uniform under the riveting force and the whole is drum shaped. But the hole expansion of the joint at 4.82 mm hole diameter is more uniform than 4.9 mm, which would lead to better joint stiffness and bearing strength. Moreover, high interference fit would cause the shear fracture of the rivet, while lower interference joints are dominated by compression-pull mixed failure. In general, the size of interference fit is an unneglectable factor in the composite riveted joints that should be thoroughly investigated. [ABSTRACT FROM AUTHOR]

The grasping transfer deformation of textile fabrics is the primary problem faced by textile production automation. During the automatic transfer process of textile fabrics, due to its own flexibility, large deformations are brought about, which leads to the problem of overlapping folds before the fabric is formed. In this paper, the end gripper composed of non-contact Bernoulli suction cups is used to adsorb and transfer the textile fabric, and the fluid structure coupling analysis method is used to calculate the adsorption force under different inlet pressures by using the macroscopic continuous model of the end effector adsorbing the fabric. The fluid structure coupling adsorption model is established, and the effects of the number and layout of suction cups and different inlet pressure on the deformation of flexible fabric during clamping are analyzed and studied. The deformation effect of the end effector in the process of transferring fabric is verified by simulation and visual experiment. The results show that the optimal working parameters of the end effector obtained by fluid structure coupling simulation are consistent with the test. When the end effector adopts five suction cups and the air inlet pressure is 0.3 MPa, the deformation is the smallest. This study provides a new method to solve the problem of automatic grasping and transfer of textile fabrics, and provides technical support for improving the automation level of garment industry. [ABSTRACT FROM AUTHOR]

This paper describes aspects within an experimental and theoretical programme aimed generally at improving the structural performance of laminated beams fabricated from Irish-grown Sitka spruce. Such timber is characterised by low density and small dimensions, is likely to distort when dried and tends to fail in tension due to the presence of knots. The well-established technique of laminating timber overcomes some of these disadvantages and the improvements are most marked with low quality donor material. It has been found that the addition of modest ratios of FRP composite reinforcement can suppress tension failure in beams. The study of failure modes, particularly in tension-reinforced beams, is the main focus of this paper. It establishes that the ultimate load capacity depends on the behavior of the timber in compression, resulting in much more consistent behavior as well as a considerable increase in flexural stiffness. [ABSTRACT FROM AUTHOR]

Auxetic woven fabrics made with special geometrical structures have gained the interest of textile scientists in recent years. This paper reports a study on auxetic woven fabric based on a double-directional parallel in-phase zig-zag foldable geometrical structure. Such a fabric has been already produced and investigated for its negative Poisson's ratio effect in two principal directions (weft and warp directions). However, its negative Poisson's ratio effect in biased tensile directions as well as under repeated tensile loading conditions has not been studied yet. Therefore, in this paper, these two limitations are addressed. The auxetic woven fabric was firstly fabricated, and then subjected not only to tensile tests in different tensile directions, including two principle directions and three biased directions, but also to repeated tensile loading. It was found that both the negative Poisson's ratio effect and the resistance to tensile deformation are dependent upon the tensile direction, and the highest negative Poisson's ratio effect and higher resistance to tensile deformation are obtained in two principal directions. [ABSTRACT FROM AUTHOR]

Continuum robots exhibit promising adaptability and dexterity for soft manipulation due to their intrinsic compliance. However, this compliance may lead to challenges in modeling as well as positioning and loading. In this paper, a virtual work-based static model is established to describe the deformation and mechanics of continuum robots with a generic rod-driven structure, taking the geometric constraint of the drive rods into account. Following this, this paper presents a novel variable stiffness mechanism powered by a set of embedded Shape Memory Alloy (SMA) springs, which can make the drive rods become 'locked' on the body structure with different configurations. The resulting effects of variable stiffness are then presented in the static model by introducing tensions of the SMA and friction on the rods. Compared with conventional models, there is no need to predefine the actuation forces of the drive rods; instead, actuation displacements are used in this new mechanism system with stiffness being regulated. As a result, the phenomenon that the continuum robot can exhibit an S-shaped curve when subject to single-directional forces is observed and analyzed. Simulations and experiments demonstrated that the presented mechanism has stiffness variation of over 287% and further demonstrated that the mechanism and its model are achievable with good accuracy, such that the ratio of positioning error is less than 2.23% at the robot end-effector to the robot length. [ABSTRACT FROM AUTHOR]

There are many engineering design problems that call for rubber components as the best solution. Vulcanized rubber has found its way into all sorts of devices, from the universal automobile pneumatic tire to the ubiquitous compliant bushing. Some high-speed rail vehicle suspensions make use of rubber, not only in the air spring itself, but also in the auxiliary spring. The mechanical characteristics of this component influence vehicle dynamics and, therefore, accurate spring models with which to conduct dynamic analysis would make for powerful design tools. Nevertheless, the mechanical behavior of rubber defies simple modeling on account of stress relaxation, creep, set, viscosity, internal friction, and nonlinear stress–strain relations. Despite the advances in the micromechanical understanding of these phenomena, as well as in the macroscopic modeling of rubber spring behavior, there is ample room for refinement, and this is precisely the goal of this paper. The mechanical behavior of a particular rubber spring for high speed rail vehicles has been characterized. The results reveal the necessary components of the model, and suggest the appropriate procedure for parameter extraction. Our model proposal consists of three elements in parallel: a nonlinear elastic spring; a “soft friction” element; and a Maxwell viscous component. The characterization procedure takes into account both stress relaxation and nonlinear elasticity. The proposed model accurately reproduces experimental results and may then be used with confidence in any type of numerical simulation. Nevertheless, for this statement to be true, the problem of “numerical softening” potentially induced by soft friction models should be resolved. The paper will show that a trailing moving average filter, seamlessly tied to the model, wipes out the softening effect. [ABSTRACT FROM AUTHOR]

Geometric parameters of 4D printed bilayer structure determine its deformation to a great extent. This paper proposed a geometric design method of 4D printed bilayer structures for accurate folding deformation. To precisely calculate the deformation, a folding deformation model of 4D printed bilayer structure is constructed considering thickness ratio and elastic modulus ratio. Then, for a target folding deformation, an adaptive surrogate-based optimization method is employed to obtain the geometric parameters of a given 4D printed bilayer structure. The numerical and physical experimental results show that the geometric parameters of 4D printed bilayer structure can be well designed by the proposed method. [ABSTRACT FROM AUTHOR]

The hypersonic waverider using the morphing configuration can improve the overall performance and broaden the flight range. On the other hand, the hypersonic waverider belongs to the lightweight construction, leading to the presence of the intrinsic elasticity. As a result, the integrated consideration of the active deformation and elastic action is important for the morphing waverider to realize global optimization. In this paper, the contro-integrated design methods are proposed for the morphing waverider to implement the trade-off analysis between the active deformation and intrinsic elasticity. First, the parametric model is built to describe the hypersonic flight characteristics. Then, the elastic dynamics is introduced to quantify the coupling responses associated with the angle of attack and elevon deflection. Furthermore, the integrated design is considered for the active deformation and inherent elastic action, and also the control law is designed to suppress the active and passive morphing disturbances. Finally, the simulation is conducted to test the effectiveness of the presented methods for the morphing waverider. [ABSTRACT FROM AUTHOR]

In this paper, variationally consistent layer-wise trigonometric shear deformation theory has been extended to deal with free vibration of two-layered laminated cross-ply plates. Governing differential equations are derived by making use of a displacement field which allows a sinusoidal variation of the in-plane displacements through the laminate thickness. In this displacement based theory, constitutive relations between shear-stress and shear-strains are satisfied in both the layers, and, therefore, shear correction factor is not required. Compatibility at the layer interface in respect of in-plane displacement and compatibility in respect of transverse shear-stress is satisfied, yet present theory contains fewer unknown variables than that of the first order shear deformation theory. Effects of rotary inertia and other inertias are also included. Efficacy of the present theory is demonstrated through illustrative examples. [ABSTRACT FROM AUTHOR]

This paper deals with elastic-plastic stress analysis of symmetric cross-ply [0/90]2 and angle-ply [30/30]2, [45/45]2, [60/60]2 aluminum metal-matrix laminated plates under thermal loads varying linearly along the thickness. The temperature is T0 at the upper and lower surfaces, respectively. The solution is performed for satisfying thermal elastic-plastic stress-strain relations and boundary conditions for small plastic deformations. Tsai-Hill Criterion is used as a yield criterion. Residual stresses distributions along the thickness of the plates are obtained. All the residual stress components are in static balance with respect to middle plane of the laminates since they are symmetric in opposite signs. The magnitude of the residual stress components is the highest at the upper and lower surfaces. [ABSTRACT FROM AUTHOR]

The paper deals with shear resistance of RC beams reinforced with fibre reinforced polymer reinforcement. The experimental programme presented here is part of an extensive research activity focused on comparing the development of shear carrying mechanisms in concrete beams reinforced with either steel or FRP reinforcement. Two sets of beams with equivalent geometrical characteristics were examined. Three beams were reinforced in flexure with conventional longitudinal steel bars and three beams with equivalent glass FRP bars. Shear reinforcement was provided in the form of transverse external links manufactured using glass fibres for the first set of beams and carbon fibres for the second. The experimental programme is described and findings of the project are reported and discussed in the context of the development of design guidelines urgently needed to support the wider use of FRP reinforcement for structural concrete applications. [ABSTRACT FROM AUTHOR]

Part I of this two-part paper presented the framework to integrate the simulation of resin flow and stress development during the manufacturing process of composites. In the current paper, the integrated approach developed in Part I for isotropic materials is extended to the case of transversely isotropic materials. Various numerical examples are considered in which the results obtained from the integrated approach are compared to those generated from the previously established models for processing induced stress development. These comparisons serve to elucidate the importance of accounting for the spatial and temporal variations in the resin volume fraction during processing and its effect on stress development. Such effects cannot be investigated in a non-integrated simulation environment where volume fraction variations due to resin flow have to be mapped sequentially from the flow simulation onto the next phase of the process simulation which treats the resin as an elastic or viscoelastic solid. [ABSTRACT FROM AUTHOR]

Electroactive polymers with time-dependent behavior are considered in the present paper by way of a new physics-based micromechanical model; such viscoelastic response is described by the internal evolution of the polymer network, providing a new viewpoint on the stress relaxation occurring in elastomers. The main peculiarity of such internally rearranging materials is their capacity to locally reset their reference stress-free state, leading to a mechanical behavior that relaxes out (eases off) an induced stress state and that can thus be assimilated to a sort of internal self-healing process. Such high deformability and recoverability displayed by dynamically cross-linked polymers can be conveniently exploited when they are coupled in electromechanical problems; the deformation induced by an electric field can be easily tuned by the intensity of the electric field itself and the obtained shape can be maintained without any electric influence once the material microstructure has rearranged after a sufficient curing time. In the present paper, both features of the polymeric material, that is, internal remodeling and electromechanical coupled response, are considered and a theoretical framework is established to simulate representative boundary value problems. [ABSTRACT FROM AUTHOR]

This research deals with the dynamic analysis of a rectangular plate made of porous materials. The porous plate is subjected to a dynamic transverse load and is resting on a Pasternak foundation. Linear poroelasticity theory is used to obtain the Biot formulation of the constitutive equations for the porous material. Also, the Young modulus and density of the porous plate vary in the transverse direction versus the porosity of the plate. Tennessee marble is the porous material that used in this paper. Reddy’s third-order shear deformation theory with five unknowns, the energy method, and Hamilton’s principle are applied to derive the equations of motion of the porous plate. These equations are solved by a differential quadrature method as a numerical method due to five coupled large equations. A detailed numerical study indicates the significant effects of aspect ratio, thickness ratio, boundary conditions, elastic medium, load intensity, and porosity on deflection of the porous plate. Results of this study can be useful to design of pneumatic conveying, handling, and control systems. [ABSTRACT FROM AUTHOR]

High Pressure Resin Transfer Molding (HP-RTM) is a new variant of composite Resin Transfer Molding (RTM) process that enables a short cycle time and a high composite strength to weight ratio, thus presents a great potential for fabricating automotive structural parts. Due to the high injection pressure, fiber-tow washout is becoming one of the major defects which impact the properties of composite materials. To predict and mitigate the fiber-tow washout problem, approaches of both experimental process optimization and computational prediction are essential. In this paper, an experimental study of fiber-tow washout is undertaken to determine the flow injection limits beyond which the preform deformation can be observed at various fiber volume fractions. A feasibility map is developed for a specific fabric and resin combination. It provides a means to determine the injection rates and fiber volume fractions to fabricate a quality part with minimal in-plane fiber washout due to the hydrodynamically flow-induced force during the HP-RTM process. [ABSTRACT FROM AUTHOR]

In this paper, we address the active deformation control of compliant objects by robot manipulators. The control of deformations is needed to automate several important tasks, for example, the manipulation of soft tissues, shaping of food materials, or needle insertion. Note that in many of these applications, the object’s deformation properties are not known. To cope with this issue, in this paper we present two new visual servoing approaches to explicitly servo-control elastic deformations. The novelty of our kinematic controllers lies in its uncalibrated behavior; our adaptive methods do not require the prior identification of the object’s deformation model and the camera’s intrinsic/extrinsic parameters. This feature provides a way to automatically control deformations in a model-free manner. The experimental results that we report validate the feasibility of our controllers. [ABSTRACT FROM PUBLISHER]

The multistage axial compressor is one of the critical components of aero-engines and plays a key role in their performance, reliability, and economy. Tip clearance has a significant impact on the performance and stability of multistage axial compressors. Due to blade and disk deformations, tip clearance will vary significantly in different operating conditions. Thus, tip clearance should be accurately estimated when evaluating compressor performance. This paper proposes a new model to predict changes of tip clearance of multistage axial compressors in different operating conditions. A first-principles approach is used to estimate the change of tip clearance caused by thermal and mechanical deformation. The span-wise temperature distribution across each stage of the multistage compressors is considered by the proposed model in this paper. The model was validated by General Electric Company (GE) E3 engine experimental results. Using the model, the performance of an 11-stage axial compressor is simulated. The results show that accounting for tip clearance variations has a 0.5% impact on the calculated mass flow rate and a 1% impact on the calculated efficiency. Thus, variations of tip clearance at different operating conditions cannot be ignored and the proposed new model is useful to accurately predict the performance of multistage axial compressor. [ABSTRACT FROM AUTHOR]

It has been demonstrated in previous research that the collision closing speed in a collision of a motorcycle or scooter with a car can be estimated on the basis of the residual crushing damage shared between the two vehicles, using an energy-derived relationship between the residual crushing damage and the collision closing speed. This paper reviews the original research and develops two further models that allow independent estimates of the collision closing speed to be calculated on the basis of either the residual deformation to the motorcycle or the residual deformation to the car. The models are validated from further crash test data taken from the literature. The principal results of the analyses are presented in the form of two predictive equations, together with the associated uncertainty that arises from the nature of the various constructions and stiffnesses of the vehicles within the population fleet. Comparison is made with other analyses in the literature. Further consideration is given to deviations from the mean estimate for subsets of the fleet population, taking into account the fact that the sides of cars have portions of various stiffnesses and that the mean stiffness of the sides of cars differed historically from those of modern models. Correction factors are presented which allows for a refined prediction based on the vehicle age and the car impact location. [ABSTRACT FROM AUTHOR]

Scissor seat suspension is used widely for attenuating the cab vibration of commercial vehicles, and obtaining its dynamics characteristics accurately is the basis of scissor seat suspension optimization, control and development. As a result, this paper focuses on the scissor seat suspension dynamics modeling and characteristics analysis. Firstly, the scissor seat suspension constraint dynamics equations are derived according to the detailed physical structure. Then, a numerical algorithm with the Baumgarte is proposed to solve the derived multi-body dynamics model which considers the correlation between generalized velocity q and acceleration q in the numerical iteration procedure. Finally, a simplified scissor seat suspension vertical dynamics model is formulated. The "spring equivalent leverage ratio" defined as the ratio of the spring vertical deformation to the relative displacement between the upper base and the lower base, as well as the "damper equivalent leverage ratio" defined as the ratio of the damper vertical velocity to the relative velocity between the upper and lower base, are proposed to study the scissor seat suspension vertical dynamics characteristics. This paper demonstrates that the proposed scissor seat suspension multi-body dynamics model provides a precise dynamics characteristics description, which can be used for the scissor seat suspension structure optimization and virtual product development. Additionally, the proposed simplified scissor seat suspension vertical dynamics model shows benefits for its control strategies development. [ABSTRACT FROM AUTHOR]

This paper aims to produce nanoscale crimped fibers using stuffer box crimping and bubble electrospinning. Nanofibers are originally obtained via a ruptured bubble and then crimped with the stuffer box crimping method. During this spinning process, the governing equations for nonlinear transverse vibration of an axially moving viscoelastic beam with finite deformation are established using the Hamiltonian principle. The crimp frequency is affected by many factors, including spinning conditions and mechanical properties of fibers. The obtained governing equations can be further used for numerical or analytical study of the crimping mechanism. [ABSTRACT FROM AUTHOR]

In this paper, a novel formulation for modeling the vibration of spatial flexible mechanisms and robots is introduced. The formulation is based on the concepts of equivalent rigid-link system (ERLS) that allows kinematic equations of motion for the ERLS decoupled from the compatibility equations of the displacement at the joint to be written. With respect to the available literature, in which the ERLS concept has been proposed together with a finite element method (FEM) approach (ERLS-FEM), the formulation is extended in this paper through a modal approach and, in particular, a component mode synthesis technique which allows a reduced-order system of dynamic equations to be maintained even when a fine discretization is needed. The model is validated numerically by comparing it with the results obtained from the Adams-Flex™ software, which implements the well-known floating frame of reference approach for a benchmark L-shaped mechanism. A good agreement between the two models is shown. [ABSTRACT FROM AUTHOR]

The effect of support spans on single-hit ballistic limit and the effect of pre-existing ballistic damage on multi-hit ballistic limit for two S-2 glass/SC15 composite laminate thicknesses (i.e. 13.6 mm and 20.5 mm) using 0.50cal fragment simulating projectiles have been experimentally investigated in a companion paper. The main objective of this paper is to simulate and correlate the multi-hit ballistic experiments using finite element analyses. One multi-hit ballistic impact scenario on two different composite laminate thicknesses is considered in the present analyses. Finite element model of the impact scenario is developed using three-dimensional solid elements and are solved using LS-DYNA and the progressive composite damage model MAT162. The MAT162 properties and parameters of plain-weave S-2 glass/SC15 composites used in the present simulations were validated in our previous work. Multi-hit impact cases are simulated by sequentially impacting the composite laminate with five different fragment simulating projectiles at five different impact locations at an interval of 200 micro-seconds. Good correlations of ballistic limit velocities between experiments and finite element analyses are obtained. In addition, finite element analyses provided time histories of projectile and laminate dynamics, and damage evolution and interactions for the multi-hit impact cases. Detailed simulation results and comparison with the experiments are presented. [ABSTRACT FROM PUBLISHER]

This paper presents a practical algorithm for the simulation of interactive deformation in a 3D polygonal mesh model. The algorithm combines the conventional simulation of deformation using a spring-mass-damping model, solved by explicit numerical integration, with a set of heuristics to describe certain features of the transient behaviour, to increase the speed and stability of solution. In particular, this algorithm was designed to be used in the simulation of synthetic environments where it is necessary to model realistically, in real time, the effect on non-rigid surfaces being touched, pushed, pulled or squashed. Such objects can be solid or hollow, and have plastic, elastic or fabric-like properties. The algorithm is presented in an integrated form including collision detection and adaptive refinement so that it may be used in a self-contained way as part of a simulation loop to include human interface devices that capture data and render a realistic stereoscopic image in real time. The algorithm is designed to be used with polygonal mesh models representing complex topology, such as the human anatomy in a virtual-surgery training simulator. The paper evaluates the model behaviour qualitatively and then concludes with some examples of the use of the algorithm. [ABSTRACT FROM AUTHOR]

The simulation of elastic human body deformation and the garment pressure distribution when wearing tight-fitting clothing is critical for the biomechanical design of functional apparel products. In this paper, we propose a new geometric interpolatory volumetric subdivision scheme over the hexahedron lattice to simulate the deformation of an elastic human body and the distribution of garment pressures. The displacement of the initial coarsest lattice of the deformed elastic human body is calculated by the iterative integration of the Lagrangian dynamic equation, which reflects the interactive reactions between the fabric and the elastic human body. The subsequent refined lattices after the deformation of initial and coarsest lattice of the human body are computed using the volumetric interpolatory subdivision scheme and eventually generate a continuous solid human body in the limit. The distribution of garment pressures is also calculated after the deformation of the elastic human body in this paper. In addition to the geometrical characteristics, we assign material and physical properties to the control vertices of the volume lattices; for example, the displacement of initial lattices of the deformed human body in this paper, and apply the same subdivision rules on the control lattices to acquire smoothly interpolated properties. This scheme is a potential method for both the dynamic and static volume modeling, and it can also be utilized in a wide range of applications. [ABSTRACT FROM AUTHOR]

A high precision triangular plate bending element proposed by the second author of this paper has been upgraded for the free vibration analysis of laminated composite right angle triangular plates. The effect of shear deformation has been incorporated. An efficient mass lumping scheme with rotary inertia has been recommended. Numerical examples of composite triangular plates having different thickness ratios, side ratios, fibre-orientations, number of layers and boundary conditions have been solved by this element. For validation of the present formulation and element few results on isotropic and orthotropic plates have been compared with those obtained from literatures. The results on composite plates have been presented as new results. [ABSTRACT FROM AUTHOR]

Weft-knitted fabric is formed by interlocking loops, which results in an unstable and easily deformable structure. In particular, fancy weft-knitted fabric exhibits diverse structural variations and uneven distribution, leading to more prominent characteristics of instability and deformation. Achieving the desired pattern effect and dimensions often requires drawing multiple designs. In this work, to obtain the geometric model of fancy fabric, mesh-loop models with movement vectors are established based on the basic structure of four stitch types: plain stitch, tuck, float, and loop transfer. The cubic Catmull–Rom spline curves are used to fit the geometric centerline of the yarn. The movement vectors are used to represent the changes in the position of the key points of the standard loops in the fancy fabric, which are derived from the analysis of the pattern grid. A physical model is established based on the force analysis of the yarn, and the positions of yarn control points are determined by solving the Euler–Lagrange dynamic equations. Through iterative calculations, the deformation effects of the fabric are obtained, enabling the simulation of fancy weft-knitted fabric. The proposed algorithms were implemented using Visual C++. The reliability and accuracy of the simulation method are demonstrated by comparing the contours of the simulation results with the actual samples. [ABSTRACT FROM AUTHOR]

This paper details a complete crush model for composite materials with focus on shear dominated crushing under a three-dimensional stress state. The damage evolution laws and final failure strain conditions are based on data extracted from shear experiments. The main advantages of the current model include the following: no need to measure the fracture toughness in shear and transverse compression, mesh objectivity without the need for a regular mesh and finite element characteristic length, a pressure dependency of the nonlinear shear response, accounting for load reversal and some orthotropic effects (making the model suitable for noncrimp fabric composites). The model is validated against a range of relevant experiments, namely a through-the-thickness compression specimen and a flat crush coupon with the fibres oriented at 45° and 90° to the load. Damage growth mechanisms, orientation of the fracture plane, nonlinear evolution of Poisson's ratio and energy absorption are accurately predicted. [ABSTRACT FROM AUTHOR]

This paper argues that the groove-wound licker-in racks' spiral mounting leads teeth with an inclination angle to the rotating direction. Theoretical analysis of forces on the fibers is carried out when the inclination angle is 0 and θ: when the teeth enter the fiber layer, the inclination angle makes the pressure on fibers increases rapidly and leads to a stronger friction force on fibers. It also leads to increases in both contact area and the wrap angle of the fiber around the teeth. This article also uses ANSYS Explicit Dynamics to simulate the fiber assembly carded by a tooth, when the inclination angle is 0°, 1° and 2°. When the inclination angle of the model is 1°, its fiber deformation is 1.35 times that of 0°; its elastic strain and stress concentration coefficient are 1.40 times than that of 0°; when the inclination angle of the model is 2°, its fiber deformation is 1.72 times than that of 0°; its elastic strain and stress concentration coefficient are 2 times than that of 0°. As with the inclinations increasing, the fiber deformations increase in time grow from 0.0634 and 0.08477 to 0.10584. The simulation also shows that when the tooth works on the fibers, there is a sudden compressive stress on fibers and then this pressure transfers with time. From all of the above, the inclination angle on licker-in teeth results in larger strain and deformation on fibers, so that this inclination angle should be decreased as much as possible in practice. [ABSTRACT FROM AUTHOR]

The deformation of rain droplet at the leading edge of a wing is critical to the aerodynamic characteristics of the aircraft under heavy rainfall and icing conditions. This study introduces the improvement of the Taylor analogy breakup and Clark models for prediction of droplet deformation near the leading edge of an airfoil. The slip velocity is considered as time-variant in the improved Taylor analogy breakup model. The viscous force is optimized in the improved Clark model. The prediction results suggest that the Clark models predict better results than the Taylor analogy breakup models. Besides, the improved Clark model has the highest prediction accuracy. However, considering the Clark model is derived based on a two-dimensional model, even the improved model still has some unavoidable deviations from the real situation. In addition, the simplified surface area in the surface tension force and the approximation of the pressure force in the original Clark model are very effective, thus are kept the same in the improved Clark model. [ABSTRACT FROM AUTHOR]

In this paper, we present a mechanical model describing the visco-hyperelastic properties of short fiber reinforced polymer composites, with the purpose to study the reinforcement and fracture mechanisms. On the basis of the Kelvin–Voigt model and deformation behavior of material, the visco-hyperelastic model is developed. The micro-structure of fibers with different distributions in polymers is taken into account. The position and orientation of the fibers are evaluated by numerical analysis, and the demonstration shows that they have a dramatic effect on the reinforcement mechanisms even for the same volume fraction. Given that the interfacial property is influenced by the interfacial region and mold flow direction, a modified function is introduced to characterize the interfacial bonding strength. Furthermore, the model provides reasonable prediction of the fracture toughness. [ABSTRACT FROM AUTHOR]

The deformable fluid actuators available on the market, i.e. pneumatic muscles and pneumatic springs, are designed to mainly exert compressive or tensile forces. This paper deals with a novel fluid deformable actuator, with three membranes, called BiFAc3, whose particular feature is the ability to exert both tensile and compressive forces. The structure of the actuator is based on three cylindrical coaxial nonisotropic membranes connected to two end plates, whose original shape allows the independent supply of the three internal chambers. The first part of the paper deals with the internal structure and the geometry of the actuator, describes the operating principle and presents a prototype. The second part presents a modelling methodology that can be used to design and analyse the actuator in dynamic applications. The mathematical model of the actuator is based on three different levels of complexity which correspond to three consecutive design stages. The model has been experimentally validated: it is a useful tool for the choice of the actuator’s geometrical dimensions, in order to satisfy specific applicative requirements. [ABSTRACT FROM AUTHOR]

The nature of the contact between the occupants and the interior structure of a vehicle following a collision is the primary cause of injury in car accidents. The interior parts of vehicles are typically made from various kinds of plastic. The deformation and failure of these materials largely determine the injury risk to the occupants. Among the various materials used to fabricate the interior parts of vehicles, plastics exhibit softening, dilatational, pressure-dependent and anisotropic characteristics, which should be considered in the design of the interior parts of those vehicles. However, it is difficult to describe the mechanical behaviour of plastics because classical models (e.g. the piecewise-linear plasticity model) using the isotropic yield criterion and the hardening rule are typically applied. Therefore, the objective of this study was to advance the numerical modelling technique for the interior materials of a vehicle and to suggest the test process for obtaining the material parameters. This paper compares the various material models that can be applied to plastics and describes a phenomenological model that includes a variable Poisson’s ratio, damage and stress–strain characteristics which are dependent on the rate of change in the applied load. Several tests were carried out to evaluate the mechanical characteristics of plastics and to obtain the parameters of the phenomenological material model. Free-motion headform impact in a pillar trim was analysed to compare the differences between the classical model and the phenomenological model. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the protective properties of warp-knitted spacer fabrics developed for protecting the human body on impact. A drop-weight impact tester was used to test the fabrics in a hemispherical form to simulate the use of impact protectors in real life. The study consists of two parts. The first part, presented in the current paper, focuses on the impact behavior of a typical spacer fabric impacted at different levels of energy. The analysis includes the impact process and the energy absorption and force attenuation properties of the spacer fabric. Frequency domain analysis is also used, to identify the different deformation and damage modes of the fabric under various levels of impact energy. The results show that the impact behavior of the fabric under impact in the hemispherical form is different from that in the planar form. The results also indicate that the curvature of the fabric can reduce energy absorption during the impact process and therefore reduce the force attenuation properties of the spacer fabric. This study provides a better understanding of the protective properties of spacer fabrics. The effect of fabric structural parameters and lamination on the protective properties of spacer fabrics under impact will be presented in Part II. [ABSTRACT FROM PUBLISHER]

This paper develops a nonlocal strain gradient plate model for vibration analysis of graphene sheets under nonuniform in-plane mechanical loads. For more accurate analysis of graphene sheets, the proposed theory contains two scale parameters related to the nonlocal and strain gradient effects. Graphene sheet is modeled via a two-variable shear deformation plate theory needless of shear correction factors. Governing equations of a nonlocal strain gradient graphene sheet on elastic substrate are derived via Hamilton’s principle. Galerkin’s method is implemented to solve the governing equations for different boundary conditions. Effects of different factors such as in-plane loading, load factor, nonlocal parameter, length scale parameter, elastic foundation, and boundary conditions on vibration characteristics of graphene sheets are examined. [ABSTRACT FROM AUTHOR]

Process modelling of thermoset matrix composites is typically divided into two distinct and sequential steps: (i) flow-compaction analysis before gelation of the resin when it behaves in a fluid-like manner, and (ii) thermomechanical analysis after gelation when appreciable modulus and thereby stress development occurs. This two-part paper presents a novel approach to integrate the simulation of resin flow and stress development seamlessly during the processing of composites. Part I lays the theoretical foundation for the simpler case of isotropic materials while Part II extends the methodology to the case of transversely isotropic materials. The formulation is implemented in a 2D plane strain finite element code written in MATLAB. Relevant numerical examples are presented to demonstrate both aspects of flow-compaction and stress development throughout the curing process of thermoset matrix composite materials. The effects of resin flow on the development and the final values of residual stresses are investigated. [ABSTRACT FROM AUTHOR]

We propose a new three-dimensional formulation based on the mixed tangential-displacement normal-normal-stress method for elasticity. In elastic tangential-displacement normal-normal-stress elements, the tangential component of the displacement field and the normal component of the stress vector are degrees of freedom and continuous across interelement interfaces. Tangential-displacement normal-normal-stress finite elements have been shown to be locking-free with respect to shear locking in thin elements, which makes them suitable for the discretization of laminates or macrofiber composites. In the current paper, we extend the formulation to piezoelectric materials by adding the electric potential as degree of freedom. [ABSTRACT FROM AUTHOR]

In this paper, free and forced vibrations, and also resonance and pulse phenomena in sandwich plates with an isotropic core and composite reinforced by wavy carbon nanotube (CNT) face sheets are studied based on a mesh-free method and first order shear deformation theory (FSDT). The sandwich plates are resting on Pasternak elastic foundation and subjected to periodic loads. In the mesh-free analysis, moving least squares (MLS) shape functions are used for approximation of displacement field in the weak form of motion equation and the transformation method is used for imposition of essential boundary conditions. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness and their mechanical properties are estimated by an extended rule of mixture. Effects of CNT distribution, volume fraction, aspect ratio and waviness, and also effects of Pasternak’s elastic foundation coefficients, sandwich plate thickness, face sheets thickness, plate aspect ratio and time depended force are investigated on the free and forced vibrations, and resonance behavior of the sandwich plates with wavy CNT-reinforced face sheets. [ABSTRACT FROM AUTHOR]

This paper focuses on the problem of parametrically excited doubly curved sandwich shells with carbon nanotubes reinforced composite (CNTRC) facesheets subjected to in-plane periodic load. The panels consist of cylindrical and spherical shells modeled using QUAD-8 element which was developed using higher-order shear flexible theory. The formulation considers the secondary effects such as the influence of in-plane and rotary inertia terms, and the aerodynamic pressure when the panel is exposed to air flow. The governing equations developed are solved based on eigenvalue approach. The limits of the principal instability zone predicted here are graphically represented using excitation frequencies against the load amplitudes. The results of this study are tested against the available solutions in the literature. A detailed study considering various design parameters including structural theories on the dynamic instability boundaries and its associated origin of instability regions is conducted. These parameters include the CNT volume content, thermal environment, aspect ratio, thickness ratio of core and facesheet, and radius of curvature. [ABSTRACT FROM AUTHOR]

Compared with regular honeycombs, irregular honeycombs are more representative of real foams, and thus more suitable for the study of foam mechanics. In this paper, the deformation and failure progression in the irregular honeycombs are investigated by analysing the images captured in order to gain an improved understanding on foam failure. Irregular honeycombs with varying cell wall thickness, cell size and cell shape were manufactured using a three-dimensional printer and tested under compression. The behaviour of irregular honeycombs is found to be different from that of regular honeycombs. In irregular honeycombs, cell walls start to fracture at some point, initially at a low speed from multiple locations. The global stress reaches its maximum value shortly after the first fracture of cell walls. Only a few cell walls buckle in the specimens with cells of irregular shape. Fracture is more likely to occur to thin and long cell walls aligned within a medium angle (around 30 to 60°) to the compressive load. However, the susceptibility of a cell wall is to fracture is also affected by its neighbouring cell walls. Strong and stiff neighbouring cell walls could shield load away and protect it from breaking. Because of this, it is better to think of a weak spot as a region, rather than an individual cell or cell wall. Overall, the more uniform cell wall size and thickness are, the better the mechanical performance of cellular solids is. [ABSTRACT FROM AUTHOR]

As a form of passive control, padding rubber layers onto the most heavily deformed zones of a system can improve the dynamic behavior and the acoustic comfort of a vehicle system. This paper proposes an extensive hybrid modal synthesis method in order to study coupled fluid-structure systems, in retaining a few degrees of freedom. Modal criteria, corresponding to noise transmission paths between substructures in the system, have been derived to characterize the dynamic phenomenon from a modal view. These criteria were then substituted by Kriging interpolation models to avoid prohibitive simulation steps during optimization of the complex system. Once the mathematical models of the investigated modal criteria were established and the multi-objective functions for rubber characteristics defined, an approximate optimal solution leading to superior dynamic performance could be obtained based on a genetic algorithm. The analytical results and numerical experiments conducted have also justified the efficiency of our proposed strategy. [ABSTRACT FROM AUTHOR]

Free vibration of a beam with multiple arbitrarily placed lateral viscous dampers is investigated to gain insight into the intrinsic dynamic features of non-proportional damped systems. In terms of virtual boundary condition method, complex modes of a damper-beam system are achieved, and the solution is also suitable for the beams that have different boundary conditions. The features of the wave numbers satisfying the frequency equation were discussed in theory. The orthogonality analysis conducted in this paper provides two orthogonality conditions for complex modes. Pseudoundamped natural frequencies, damping ratios and complex modes are surveyed via numerical study. The analysis on the evolution of complex modes shows that the increasing damping would lead to over damped modes, and the mode shape that corresponds to the small one of a pair of real-valued natural frequencies is close to the static deformation shape of a beam subjected to static forces located at the positions of the dampers. For the rest modes that would never be over damped with increasing damping, the mode shapes and corresponding psuedoundamped natural frequencies will converge to that of a beam with rolling supports located at where dampers are placed. The exact solution of free vibration of a multiple-span beam is presented in addition. [ABSTRACT FROM AUTHOR]

Existing extension-twist coupling in composite tubes can result in undesirable deformations, which may in turn interfere with their normal performance. In this work, a quantitative factor was developed to examine the existence of such coupling in circular composite tubes using the non-classical composite beam theory. The theoretical formulation considered transverse shear and three-dimensional (3D) elastic effects in laminated walls. Therefore, the coupling factor can be used in both thin-walled and thick-walled composite tubes. The numerical values for the coupling factor calculated using the present approach were compared to those obtained from a 3D validated finite element model on 10 composite tubes with different stacking sequences. The findings suggested that the coupling factor could accurately detect existing coupling between extension and twist in composite tubes regardless of their stacking sequence. The paper also proposed a number of design guidelines that could be used in order to eliminate the extension-twist coupling in composite tubes. [ABSTRACT FROM AUTHOR]

Large space structures experience changing thermal environment during orbiting the earth. The resultant temperature gradients induce structural deformations that may downgrade performance of payloads conducting high precision missions and even affect stability of the spacecraft. So, it is extremely important to analyze thermally induced deformation of large space structures for routine operation. In this paper, the ultra-large truss support membrane structure on satellite is characterized and studied. The methodology of thermal quasi-static deformation is formulated and the procedure of thermo-structural analysis is proposed. The thermostructural analysis model with hollow tubes is developed based on finite difference method and finite element method. With heat fluxes from solar radiation, earth radiation, and earth albedo radiation being considered, the temperature distribution filed is obtained from the thermal analysis and then applied to the structural analysis model to calculate quasi-static deformations and root mean square errors with orbital angles. Results show that temperature gradients along circumferential direction of tubes can induce prominent shape error. The proposed method is useful for predicting thermally induced deformation of large space structures and valuable for designing active control systems to compensate for disturbances. [ABSTRACT FROM AUTHOR]

Multi-segment shell typical of underwater vehicles is currently important underwater equipment. Stealth performance is a key indicator to improve the working capacity of underwater vehicles. Low-noise design is an important means to improve stealthy performance. Accurate and effective identification of its structure Frequency Response Function (FRF) is the premise of low-noise design. However, the multi-section shell joint interface has many connection points, complex transmission path and typical nonlinear characteristics, which challenges the acquisition of its structural FRF. The Receptance Coupling Substructure Analysis (RCSA) is used to segment the multi-stage shell, which can realize the integration of finite element method and experimental method, and provide an effective way to obtain the FRF of multi-segment shell. At the same time, the multi-segment shell is a typical thin-wall structure, and its actual buckling process under impact is a nonlinear (large deformation) process. Therefore, the nonlinear joint interface is constructed based on linear connection, and the RCSA for nonlinear joint interface is studied. On the basis of accurately obtaining the FRF, it is of theoretical and application significance to study the low noise design of shell. [ABSTRACT FROM AUTHOR]