Macro-mechanical Model Research Articles

Modeling and Analysis of Resistance-Sensing Characteristics for Two-Way Shape Memory Alloy-Based Deep-Sea Actuators

Deep-sea actuators based on shape memory alloys (SMAs) are an emerging frontier field of multidisciplinary crossover, and the resistive sensing characteristics are the basis for the drive control of SMA deep-sea actuators. The resistance and resistivity of SMAs are complex and highly dependent on temperature and stress, and there is no complete description of SMAs for extreme environments of high pressure, low temperature, and high salinity in the deep sea. In this study, the logistic function is introduced to improve the kinetic equation of phase transition, and the macromechanical model, the law of resistance, and the resistivity mixing rule are integrated to model and analyze the resistive self-awareness characteristics of two-way shape memory alloy deep-sea actuators. The complex coupling relationships among resistance, strain, stress, resistivity, and temperature under constant load conditions are investigated, and the validity of the resistance-sensing model is verified by the water bath cycling test. The results show that the predicted values of the model agree well with the measured values. The self-perceived relationship between the resistance and deformation of the two-way shape memory alloy can be effectively expressed, which provides theoretical model support for the design of memory alloy deep sea actuators and sensorless drive control.

FlexScale: Modeling and Characterization of Flexible Scaled Sheets

We present a computational approach for modeling the mechanical behavior of flexible scaled sheet materials---3D-printed hard scales embedded in a soft substrate. Balancing strength and flexibility, these structured materials find applications in protective gear, soft robotics, and 3D-printed fashion. To unlock their full potential, however, we must unravel the complex relation between scale pattern and mechanical properties. To address this problem, we propose a contact-aware homogenization approach that distills native-level simulation data into a novel macromechanical model. This macro-model combines piecewise-quadratic uniaxial fits with polar interpolation using circular harmonics, allowing for efficient simulation of large-scale patterns. We apply our approach to explore the space of isohedral scale patterns, revealing a diverse range of anisotropic and nonlinear material behaviors. Through an extensive set of experiments, we show that our models reproduce various scale-level effects while offering good qualitative agreement with physical prototypes on the macro-level.

Manufacturing, characterization, and macromechanical modeling of short flax/hemp fiber-hybrid reinforced polypropylene

The present work focuses on the manufacturing, mechanical characterization, and modeling of hybrid Flax/Hemp/Polypropylene (PP) composites under dry conditions. Geometric parameters of the fibers were measured both before and after the melt processing. The results indicated that the processed fibers, especially the hybrid ones, had a narrowed length distribution with an average fiber length of 0.48 mm for hybrids compared to 0.62 mm for non-hybrids. The hybrid composites were mechanically characterized using basic and loading-unloading tensile tests with various fiber combinations and weight percentages. The study also examined the effect of strain rate and cutting angle on the behaviors of the composites. The results demonstrated the significance of fiber orientation as the primary factor in explaining mechanical variations. The tensile strength and Young's Modulus of FH30 composites (PP + 15 wt% flax + 15 wt% hemp) increased by about 24.1 % and 10.9 %, respectively, when the plates were cut into dumbbell shapes at a 90° angle to the injection molding flow direction, compared to a cut at 0° The study also showed that the tensile strength is directly proportional to the mass fraction of reinforcements, with an increase in tensile strength by 7.9 % for 0° cut angle specimens between FH10 (PP + 5 wt% flax + 5 wt% hemp) and FH30 bio-composites, while the uniform strain is inversely proportional to the mass fraction of reinforcements, evidenced by a reduction in uniform strain of 30 % between FH10 and FH30 samples. Morphological observations revealed the presence of bands indicating the propagation of micro-cracks, as well as debonding or cohesive failure. Finally, a Perzyna-type elasto-viscoplastic constitutive model was applied to accurately predict the overall mechanical response of a hybrid composite material. Specifically, the model successfully captured the tension deformation behavior of hybrid natural short-fiber thermoplastic composites, including the elastic stage, yield stress, and nonlinear hardening.

Nonlinear Deflection Characteristics of Weakly Bonded Curved Composite Structure Under Hygro-Thermo-Mechanical Loadings

A customized MATLAB algorithm is developed for internally separated laminated composite panels experiencing large geometric deformations. The algorithm is designed to calculate nonlinear deflection responses under the effect of combined hygro-thermo-mechanical (HTM) loading. The hygrothermal (HT) load on the panel is in-plane, whereas the mechanical load acts upon the structure transversely. The analysis has adopted various kinematic theories and finite element (FE) techniques to determine the deformations computationally. The deflection behavior of the composite is characterized through a macro mechanical model considering the nonlinearity in geometry with and without accounting for the stretching effects across the panel thickness. Additionally, the changes in composite properties due to the environment and/or loadings are adopted to achieve a realistic response, preserving continuity assumptions between the individual layers of the weakly bonded structure. Moreover, various numerical examples are examined through different models to illustrate the influences of environmental factors and design-specific parameters on the flexural strength of weakly bonded structures. The findings strongly emphasize the necessity of employing diverse kinematic models when examining laminated structures, both with and without HT loading, while also acknowledging the potential for debonding.

A multiscale finite element analysis model for predicting the effect of micro-aeration on the fragmentation of chocolate during the first bite

The emerging need to reduce the calorific value of foods, while simultaneously improving the consumer perception drives the quest for developing new food structures that satisfy both criteria. Aiming to shed light on the influence that micro-aeration has on the breakdown of chocolate during the early stages of the oral processing, this paper summarises the development of multi scale, in silico Finite Element (FE) models for the first bite. A micro-mechanical analysis was first employed to predict the impact on the mechanical properties of chocolate at two microaeration levels, i.e. f=10vol% and f=15vol%. The estimated elastic, plastic and fracture properties from the micromechanical model were subsequently fed into a macroscopic simulation of the first bite. Both micromechanical and the macromechanical models for the 10vol% and 15vol% porosity chocolate are compared to experimental data for validation purposes. The micromechanical models are compared to data from literature on mechanical testing of the same two chocolate materials whereas the first bite macromechanical model was compared to in vitro experimental data obtained in this study using a 3D printed molar teeth test rig mounted to a mechanical tester. Finally, the particle size distribution of the fragmented chocolate during the first bite was estimated from the in silico model and compared to in vivo literature data on the same chocolate materials and in vitro experimental data from this work. All comparisons between the in silico models and the in vitro/in vivo data led to good agreement. Our modelling methodology provides a cost-efficient tool for the investigation of new food structures that reduce the calorific value while enhancing the taste perception.

Modelling fracture due to corrosion and mechanical loading in reinforced concrete

Corrosion in reinforced concrete is an important feature which can lead to increased deformation and cracking, as well as to premature failure. In the present work, macro-mechanical modelling of corrosion is performed, namely the degradation of bond–slip between concrete and steel. A mixed-mode damage model is adopted, in which the interaction between the bond–slip law and the stress acting in the neighbourhood of the concrete–steel bar interface is taken into account. Bond–slip degradation is modelled using an evolutionary bond–slip relationship, which depends on the level of corrosion. Different relevant loading cases are studied. Special attention is given to the evolution of corrosion in time, under constant load. This is done by adopting a Total Iterative Approach, in which the structure is reevaluated each time step, upon damage increase due to corrosion. Pullout tests are presented to illustrate the performance of the model. Bending tests are also performed to evaluate the influence of corrosion at structural level.

Parametric analysis and numerical optimisation of spinach root vibration shovel cutting using discrete element method

Shovelling the soil and cutting the roots is the first step in harvesting the whole spinach plant, which determines the movement state of spinach plants, the state of soil fragmentation and root soil separation force. Therefore, it is necessary to thoroughly study the process of shovelling the soil and cutting the roots. Firstly, micromechanical and macromechanical models of shovel cutting were built. It was induced that vibration shovel cutting was conducive to soil fragmentation and root-soil separation by the theoretical models. Secondly, a vibration shovel cutting mechanism was proposed. In order to study the interaction mechanism of root-soil-shovel, a root-soil composite discrete element model was established and calibrated. Vibration shovel cutting simulation test was carried out based on the model. The effects of three vibration shovel cutting parameters (vibration amplitude, vibration frequency and cutting speed) on the number of bond by bonding (BOND) breakage, root-soil movement law, soil uplift height and root-soil separation in normal vibration, tangential vibration and non-vibration were analyzed. BOND breakage was conducive to spinach aggregation and root-soil separation by simulation analysis. As determined by response surface analysis, the optimal combination of parameters for the maximum number (80363) of BOND breakage and the minimum soil uplift height (19.4 mm) was vibration amplitude of 3 mm, vibration frequency of 40 Hz and cutting speed of 0.3 m/s. Finally, the vibration shovel cutting model was verified experimentally by field tests. This study provides a method to study the interaction mechanism of root-soil-shovel.

A Macromechanical Constitutive Model for Rebar Buckling

Rebar buckling and fracture have been experimentally observed to cause significant degradation of the mechanical properties of reinforced concrete (RC) elements and should be accounted for in the analysis of RC structures. While data on the material properties of steel rebar are widely available, test data on rebar buckling remain scarce. This paper proposes a macromechanical model capable of predicting rebar buckling responses solely on the basis of steel material properties and the rebar geometry, even when rebar buckling experimental data are not available. This is achieved by computationally building the uniaxial stress-strain constitutive response at each analysis step through the equilibrium in the deformed configuration of the buckled rebar and through the cross-sectional constitutive response. The equilibrium in the deformed configuration is treated in a manner consistent with the corotational formulation, while the cross-sectional constitutive response is built through integration of a uniaxial damage plasticity model over the cross-section area. Rebar buckling is triggered by an initial imperfection, while low-cycle fatigue effects are reproduced through the uniaxial damage plasticity steel material model, without the need for cycle-counting algorithms. The proposed model is translated to a computer code, calibrated to a set of experimental data, validated to separate test data, and subsequently used in the analysis of an experimentally studied RC column that experienced rebar buckling under cyclic loading. Using the proposed model, the analysis captured the response of the RC column and the experimentally observed strength deterioration due to rebar buckling.

Orthotropic multisurface model with damage for macromechanical analysis of masonry structures

A novel macromechanical model with damage for the analysis of masonry structures in-plane loaded is presented. The model accounts for the directional mechanical properties typically characterizing response of masonry with regular texture. Indeed, the real heterogeneous material is modeled as a fictitious homogenized medium with orthotropic elastic constitutive behavior along the masonry natural axes, identified as the parallel and normal directions to bed joints orientation. The different strength characteristics along each material axis are taken into account by properly defining a damage matrix, which accounts for failure mechanisms due to axial tensile and compressive states, as well as shear. A suitable criterion is introduced, resulting in a damage limit surface geometrically defined in the space of the damage associated variables by the intersection of two ellipsoids and an hyperboloid. The model is implemented into a finite element procedure where the mesh-dependency numerical issue is avoided by adopting a nonlocal integral formulation. Validation examples, involving simple uni-axial and bi-axial tests, as well as more complex loading conditions, are provided to prove the model performances at both material and structural scale.

A component-based macro-mechanical model for inter-module connections in steel volumetric buildings

Inter-module connections (IMC) are a research focus closely related to the robustness of steel volumetric buildings (VB). Many IMC have been proposed by numerous researchers and engineers, experimentally tested and numerically studied using finite element models. However, there are insufficient IMC macro models available, which imposes challenges for engineers to construct a global numerical VB model. Hence, this study aims to close the gap with a component-based macro-mechanical model for the macro-modelling of IMC in steel VB. In this paper, a comprehensive IMC database was collected to identify and characterise the active components. Two types of macro-mechanical models (H-shape and Q-shape) consisting of P-V-M links have been proposed and a novel uplifting mechanism has been derived for a typical IMC (bolted tie plate with shear key). The proposed macro-mechanical model and other existing macro-models were then compared with existing pushover experiments from an IMC subassembly. The proposed macro-mechanical model shows a good match to the existing experimental results, and it is adaptable to existing IMC.

Numerical investigation of the compressive behavior of 2.5D woven carbon-fiber (2.5D-CFRP) honeycomb and experimental validation

In this work, the quasi-static compression behavior of a 2.5D woven carbon-fiber (2.5D-CFRP) honeycomb was numerically investigated by using two optimized models based on a conventional macro-mechanical model and the representative volume element (RVE) model. We introduced a viscosity regularization criterion into the conventional macro-mechanical model to improve the accuracy of the simulations. The relationship between the viscosity coefficient and simulation accuracy was analyzed using the displacement-load profile of the 2.5D-CFRP honeycomb under quasi-static compression. We further clarified the damage mechanism during the crushing of the 2.5D-CFRP honeycomb. An RVE model simulation was performed by using the combined VUMAT subroutine, which represented the damage state of fibers in different lay-up directions of the 2.5D-CFRP honeycomb. The results showed that the modified macro-mechanical model represented the twisting and folding mechanism of the honeycomb walls during quasi-static compression rather than the damage of the fibers at the intersection of the honeycomb walls.

Investigation on microstructure evolution of clayey soils: A review focusing on wetting/drying process

Variability in moisture content is a common condition in natural soils. It influences soil properties significantly. A comprehensive understanding of the evolution of soil microstructure in wetting/drying process is of great significance for interpretation of soil macro hydro-mechanical behavior. In this review paper, methods that are commonly used to study soil microstructure are summarized. Among them are scanning electron microscope (SEM), environmental SEM (ESEM), mercury intrusion porosimetry (MIP) and computed tomography (CT) technology. Moreover, progress in research on the soil microstructure evolution during drying, wetting and wetting/drying cycles is summarized based on reviews of a large body of research papers published in the past several decades. Soils compacted on the wet side of optimum water content generally have a matrix-type structure with a monomodal pore size distribution (PSD), whereas soils compacted on the dry side of optimum water content display an aggregate structure that exhibits bimodal PSD. During drying, decrease in soil volume is mainly caused by the shrinkage of inter-aggregate pores. During wetting, both the intra- and inter-aggregate pores increase gradually in number and sizes. Changes in the characteristics of the soil pore structure significantly depend on stress state as the soil is subjected to wetting. During wetting/drying cycles, soil structural change is not completely reversible, and the generated cumulative swelling/shrinkage deformation mainly derives from macro-pores. Furthermore, based on this analysis and identified research needs, some important areas of research focus are proposed for future work. These areas include innovative methods of sample preparation, new observation techniques, fast quantitative analysis of soil structure, integration of microstructural parameters into macro-mechanical models, and soil microstructure evolution characteristics under multi-field coupled conditions.

Study on the interface toughening of particle/fibre reinforced epoxy composites with molecularly designed core–shell particles and various interface 3D models

Poor interface toughening reduces the utilisation of particle/fibre-reinforced thermoset polymer composites in many engineering applications. Numerous studies have been performed on polymer and fibre component modifications, yet utilising fillers in epoxy is a promising way to improve interface toughness. Here, a molecularly designed core–shell particle (CSP) is introduced into the epoxy polymer to generate a strong interface through an epoxy coupling agent acrylate shell and styrene-butadiene rubber core. The nanocomposite material, in particular, has an excellent tensile strength of 166% and exceptional elongation of 245%; these properties further improve the interlaminar shear strength of 225% in carbon fibre-reinforced polymer composite. Moreover, CSP gives better shear effects and stress transferability to the fibre–matrix interface region. It was clarified systematically by developing a 3D micro- and macro-mechanical model from field emission scanning electron microscopy (FESEM) and surface fracture analysis. Meanwhile, results suggest that effective toughness is achieved by well-dispersed and void growth, filler-epoxy interaction and strong matrix-fibre interfaces. With these features, this study emphasises a way to analyse composite structures and fibre laminates which can help engineering design strategies for various applications.

Cyclic compression behaviour of multilayered nanostructured foams: Numerical meso scale modelling and experimental validation

In the present paper the mechanical fatigue behavior of a complex porous and hierarchical structure at a macroscopic scale is investigated from the experimental point of view. A numerical model describing the cyclic behavior is developed considering the geometric structure of the foam and the constitutive model, using a macro-mechanical hyperelastic material Ogden models. The coated open cell foam is characterized by Representative Volume Element of Finite Elements (FEA-RVE) model at the mesoscale with periodic boundary conditions. The RVE model is based on the microscopic foam topology and density, then a tessellation is applied to randomly generate the inner structure. The FEA model is then inserted, and the overall response is validated and calibrated from quasi-static and fatigue compression tests run at two different frequencies. The mesoscale model is used to simulate the mechanism involved in the compression of PU hierarchical composite foams, the structure buckling and the dissipated energy.

Configurational forces in ferroelectric structures analyzed by a macromechanical switching model

Polycrystalline ferroelectric ceramics are widely used in sensors, actuators, microelectromechanical systems, etc. If a ferroelectric structure possesses some defects like voids or inhomogeneities, its reliability is reduced, and undesired non-homogeneous local concentrations of the electromechanical fields occur. Under the applied external loading, a domain switching region evolves in the vicinity of defects, which is manifested as a reorientation of the remanent polarization vector. In the current work, the nonlinear electromechanical behavior of ferroelectric ceramics is computed by means of three-dimensional finite element analysis, using the phenomenological continuum mechanics model suggested by Landis (J. Mech. Phys. Solids 50(1):127–152, 2002. https://doi.org/10.1016/s0022-5096(01)00021-7) and numerically implemented by Stark (Int. J. Solids Struct. 80:359–367, 2015. https://doi.org/10.1016/j.ijsolstr.2015.09.004). This constitutive law is combined with user-developed elements in Abaqus commercial code for nonlinear coupled electromechanical analyses. By use of the numerical simulations, the evolution of all field variables, in particular of the polarization, is tracked. In a post-processing step, the configurational forces are computed, which express the thermodynamic driving forces acting on the defect. As a typical defect, we consider a circular void in the ferroelectric structure exposed to an alternating electric field. Additionally to the void, other inhomogeneities, namely, a strip of dissimilar material as well as dielectric and piezoelectric inclusions, are investigated. For all cases, the redistribution and evolution of the configurational forces are studied. Besides the essential findings and methodology achieved in this work, the developed software can serve as a basis for further investigations on the failure of composite smart structures and explicit crack modeling using fracture mechanical concepts.

Numerical hygrothermal frequency of pre-damage shallow shell panel: A nonlinear FE approach

ABSTRACT In this work, the nonlinear eigenvalues of the debonded composite panel (flat, single and doubly curve) are evaluated under unlike humidity and temperature conditions. To obtain the said modal responses a macro mechanical isoparametric finite element-based numerical model of pre-damage laminated composite is developed. The structural panel deformations are counted through two different kinematic theories with small deviations (related to the drilling degrees of freedom). The geometrical distortions of the panel component are expressed using the common Green’s strain relation in Lagrangian scope. The governing differential equation (converted to nonlinear eigenvalue equations) is derived from a dynamic version of the variational principle. The direct iterative approach has been adopted to compute the nonlinear frequencies in association with the finite element steps. Also, the element sensitivity behavior of the obtained numerical solution is verified and extended further to check the efficacy (comparing the results from the published domain). In continuation, the nonlinear modal values are computed through a series of examples considering the role of debonding with the structural parameters in detail.

FE-based damage modeling approach for short fiber reinforced thermoplastics under quasi-static load coupling anisotropic viscoplasticity and matrix degradation

It is challenging to predict the material degradation and crack initiation of short fiber reinforced thermoplastics (SFRT) components with high computation efficiency and low parameter identification effort. To achieve that, this work utilizes a hybrid method combining micro- and macro-mechanical approaches to describe the damage-coupled material behavior of SFRT. The Mori-Tanaka mean-field homogenization method is used to determine the effective linear elastic properties of SFRT, whereas the consideration of plasticity is based on a macro-mechanical anisotropic viscoplastic model. The effect of micro-damage in the matrix material on the macroscopic behaviors of SFRT is considered within the Continuum Damage Mechanics (CDM) framework. A nonlinear damage evolution law is implemented to account for the nonlinearity in the damage evolution. Targeting industrial applications, the proposed damage-coupled material model is implemented into the commercial FE software ANSYS with a novel stepwise damage updating process, requiring no user-defined subroutine. The model is calibrated with experimental data on flat specimens under monotonic and cyclic tensile loading. The FE simulation with the calibrated material model accurately describes the anisotropic deformation and crack initiation of the investigated SFRT material observed in experiments.

Theoretical study including physic-based material model to identify underlying effect of vibration amplitude on residual stress distribution of ultrasonic burnishing process

The potential of distribution of compressive residual stress at deep surface layers caused by ultrasonic-based surface sever plastic deformation (SSPD) has attracted researchers' attention to deeply study the mechanism of the process by simulation models. In majority of the researches, macro-mechanical Johnson-Cook (JC) model was utilized to govern material constitutive behavior. However, the large differences between measured and predicted values of residual stress of some materials imply that the underlying mechanism is still unclear and merits further studies. In the present work, a new physics-based constitutive equation incorporating micromechanics of initial grain size, dislocation evolution, dislocation drag and acoustic softening has been developed to obtain plastic flow stress. Then, the mechanic of the ultrasonic burnishing process incorporating superposition of static and dynamic loads was simulated using concept of expanding cavity model (ECM). The residual stress has been further calculated through combination of developed models aiming to discover the undying mechanism of vibration amplitude effect on stress fields. In order to confirm the obtained results, series of ultrasonic burnishing experiments have been carried out on AA6061-T6 under different vibration amplitude. The obtained results revealed that the developed analytical models of residual stress field are considerably more accurate than those previously established that took the macro-mechanical constitutive models to calculate plastic flow stress. Through the developed simulation model, it was studied in depth that how the vibration amplitude as the most adjustable ultrasonic vibration parameter determine variation of residual stress field. It has been demonstrated that the acoustic softening because of presence of ultrasonic energy field has the greatest impact in generation of compressive residual stress in surface and beneath layers.

Design, Analysis, and Modeling of Curved Photovoltaic Surfaces Using Composite Materials

Currently, the use of photovoltaic solar energy has increased considerably due to the development of new materials and the ease to produce them, which has significantly reduced its acquisition costs. Most commercial photovoltaic modules have a flat geometry and are manufactured using metal reinforcement plates and glass sheets, which limits their use in irregular surfaces such as roofs and facades (BIPV) and the transportation sector (VIPV). The purpose of this study is to analyze the design implications of curved photovoltaic surfaces using composite materials. Considering operation and maintenance requirements, the most suitable reinforcement and encapsulation materials are selected based on references and experimental tests. It was found that the maximum radius of curvature that a polycrystalline silicon cell with the dimensions of a SunPower C60 model can achieve is 6.51 m for a failure probability lower than 5 %, which allows us to define the maximum curvature that this photovoltaic surface can reach. Additionally, an analytical model of the reinforcement was implemented using macromechanical models in Matlab™, which was validated by the finite element method employing the composite materials module in Ansys®. Therefore, this paper presents a detailed analysis of the shear stresses between the layers and of the deformations generated in the curved solar panel reinforcement. Finally, under the operating conditions assumed here, carbon fiber presents the best structural behavior in the reinforcement material, while epoxy resin exhibits a better performance in the encapsulation material. These results can facilitate the manufacturing of curved photovoltaic surfaces.

Low-temperature elasticity of amorphous polymers: Molecular model and rheological equation

A molecular-kinetic model of the processes of highly elastic deformation of amorphous polymers is proposed and, on its basis, nonlinear rheological equations are obtained; these latter make it possible to describe these processes under changes of deformation conditions in a wide range: temperature, deforming stress, and strain rate. A connection of the nonlinear micromechanical model of a polymer with the classical macromechanical model of a standard linear body is established. The transitions between the structural-deformation states of a warm and frozen elastomer, as well as the effects of low-temperature deformation melting and quantum elasticity of an amorphous polymer, are discussed.