Effective Mechanical Parameters Research Articles

A procedure for the identification of effective mechanical parameters of additively manufactured elements using integrated ultrasonic bulk and guided waves

The subject of the current work was a simple but robust novel two-stage procedure for the non-destructive determination of effective elastic constants using ultrasonic wave propagation. First, ultrasonic bulk wave velocities measured on cubic samples were used to calculate most of the elements of the stiffness matrix. Secondly, the remaining elements were determined using the dispersion curves of elastic guided waves measured on plate samples. Based on the complete stiffness matrix it was possible to calculate the complete set of effective elastic constants. The algorithm was verified for AM elements produced from PLA filament satisfying the conditions of transversely isotropic and orthotropic material models. For the transversely isotropic samples, Young’s moduli (E) varied from 2.6 to 2.9GPa, shear moduli (G) equalled between 0.9 and 1.2GPa, whereas Poisson’s ratios (ν) ranged between 0.20 and 0.32. In orthotropic sample the corresponding values were: E = 1.3–2.8GPa, G = 0.6–1.2GPa, and ν = 0.07–0.59. The results of the current study have been compared with references from the literature, giving satisfactory agreement.

Effective mechanical parameters of bone tissue samples for the selection of individual osteoimplants

Effective mechanical parameters of bone tissue samples for the selection of individual osteoimplants

Study on Dynamic Characteristics of a Rotating Sandwich Porous Pre-Twist Blade with a Setting Angle Reinforced by Graphene Nanoplatelets

Lightweight blades with high strength are urgently needed in practical rotor engineering. Sandwich structures with porous core and reinforced surfaces are commonly applied to achieve these mechanical performances. Moreover, blades with large aspect ratios are established by the elastic plate models in theory. This paper studies the vibration of a rotating sandwich pre-twist plate with a setting angle reinforced by graphene nanoplatelets (GPLs). Its core is made of foam metal, and GPLs are added into the surface layers. Supposing that nanofillers are perfectly connected with matrix material, the effective mechanical parameters of the surface layers are calculated by the mixing law and the Halpin–Tsai model, while those of the core layers are determined by the open-cell scheme. The governing equation of the rotating plate is derived by employing the Hamilton principle. By comparing with the finite element method obtained by ANSYS, the present model and vibration analysis are verified. The material and structural parameters of the blade, including graphene nanoplatelet (GPL) weight faction, GPL distribution pattern, porosity coefficient, porosity distribution pattern, length-to-thickness ratio, length-to-width ratio, setting angle and pre-twist angle of the plate are discussed in detail. The finds provide important inspiration in the designing of a rotating sandwich blade.

Эффективные механические характеристики симметричного слоистого композита при различных условиях нагружения

Object and purpose of research. This paper discusses balanced and quasi-isotropic (in the reinforcement plane) symmetric layered composite structures made up by the layers of cloth-reinforced GRP. The purpose of this work was to demonstrate the necessity to justify the applicability of experimental results for effective mechanical parameters determined in the conditions of uniaxial tension/compression to the calculation of thin-walled layered composite structures that work in bending/twisting conditions. Materials and methods. The straining of layered composite structures is simulated as per the updated theory of first-order plates, the model of complex moduli and the principle of elastic-viscoelastic correspondence in linear viscoelasticity theory. Limit state predictions are based on Tsai-Wu tensor-polynomial strength criterion. Main results. This paper suggests the expressions that predict effective elastic constants, dissipation properties and strength limits for symmetric layered structures under investigation. The study shows that balanced symmetric structure made up by four layers of composite may be regarded, with the accuracy sufficient for engineering calculations, as an ortho-tropic material for all loading conditions. At the same time, symmetric quasi-isotropic (in the reinforcement plane) structure made up by thirty two composite layers must be regarded as orthotropic in case of tension/compression and monoclinic in case of bending/twisting. Conclusion. The study has shown the necessity to justify the application of experimental effective mechanical properties for uniaxial tension/compression to calculation of thin-walled layered composite structures exposed to bending/twisting.

Mechanical response of dot-by-dot wire-and-arc additively manufactured 304L stainless steel bars under tensile loading

With the advent of a new arc-based additive manufacturing (AM) process, referred to as Wire-and-Arc Additive Manufacturing (WAAM), the scale of the metal printed parts increased up to several meters, thus becoming suitable for large-scale applications in marine, aerospace and construction sectors. However, specific considerations in terms of geometrical and mechanical properties ought to be made in order to effectively use the printed outcomes for structural engineering purposes. The introduction of the novel printing strategy referred to as “dot-by-dot”, consisting in successive drops of molten metal, enabled the use of WAAM for complex lattice structures, made by continuous grids of WAAM bars. Nevertheless, their proper design requires an accurate evaluation of the influence of the non-negligible inherent geometrical irregularities on the mechanical response of the bars. Hence, extensive experimental work is needed in order to evaluate the mechanical response of WAAM bars with geometrical imperfections.The present study is thus focused on the assessment of the mechanical response in tension of WAAM-produced 304L stainless steel small bars in terms of key effective mechanical parameters. As such, the mechanical characterization through tensile tests is supported by microstructural investigations and detailed studies on the geometrical features. Three batches of bars are studied, each one printed at different build angles representative of limit cases for practical applications. The microstructural analysis confirms the preferential grain orientation typical of WAAM process for all three build angles. The results of the geometrical and mechanical characterization clearly evidence the non-negligible influence of the inherent geometrical imperfections on the mechanical response in tension of the printed bars, with a detrimental effect of the build angle on the main key effective mechanical parameters. Overall, the results highlight the need of specific investigations on both geometrical and mechanical properties of WAAM bars for structural design purposes.

Bayesian inversion for unified ductile phase-field fracture

The prediction of crack initiation and propagation in ductile failure processes are challenging tasks for the design and fabrication of metallic materials and structures on a large scale. Numerical aspects of ductile failure dictate a sub-optimal calibration of plasticity- and fracture-related parameters for a large number of material properties. These parameters enter the system of partial differential equations as a forward model. Thus, an accurate estimation of the material parameters enables the precise determination of the material response in different stages, particularly for the post-yielding regime, where crack initiation and propagation take place. In this work, we develop a Bayesian inversion framework for ductile fracture to provide accurate knowledge regarding the effective mechanical parameters. To this end, synthetic and experimental observations are used to estimate the posterior density of the unknowns. To model the ductile failure behavior of solid materials, we rely on the phase-field approach to fracture, for which we present a unified formulation that allows recovering different models on a variational basis. In the variational framework, incremental minimization principles for a class of gradient-type dissipative materials are used to derive the governing equations. The overall formulation is revisited and extended to the case of anisotropic ductile fracture. Three different models are subsequently recovered by certain choices of parameters and constitutive functions, which are later assessed through Bayesian inversion techniques. A step-wise Bayesian inversion method is proposed to determine the posterior density of the material unknowns for a ductile phase-field fracture process. To estimate the posterior density function of ductile material parameters, three common Markov chain Monte Carlo (MCMC) techniques are employed: (i) the Metropolis–Hastings algorithm, (ii) delayed-rejection adaptive Metropolis, and (iii) ensemble Kalman filter combined with MCMC. To examine the computational efficiency of the MCMC methods, we employ the hat{R}{-}convergence tool. The resulting framework is algorithmically described in detail and substantiated with numerical examples.

Laboratory study and measurement of stiffness and compaction of unsaturated clay soil by using the innovative rebound hammer

Defining soil behavioral parameters, which eventually results in predicting every short-term and long-term soil behavior, has continually been one of the interests of soil mechanics and has been of exceptional value. To this end, in this study, a novel method has been reviewed to determine the compressive behavior of fine-grained soils in the laboratory and the field, without sampling by the patented electronic device. In the lab, homogeneous materials of the intended soil underwent the compaction test, mechanical and physical tests, direct shear test, and impacts of the innovative rebound hammer in the horizontal and vertical directions in the test-box. The impact shear waves produce resistance and voltage output by force and dislocation sensors with high-sensitivity proportional to the pressure based on the soil surface stiffness. The obtained voltages are then converted to digital by an analog-to-digital converter and a microcontroller. Next, a number is shown on display by the "CodeVision" program. Then, by solving a quasi-dynamic equation (Viscoelastic spring-damper model) by MATLAB software and with the aid of laboratory-field results and correlation equations, a fitting connection between all effective mechanical soil parameters has been estimated to an acceptable extent. The effective mechanical parameters of the soil include the compaction percentage, specific gravity, and frequency of the system in the damped and non-damped states, the energy imposed on the soil, and the plastic stage strain in the range of less than 15% humidity. The results determine that increased hammering numbers are directly related to increased soil compaction and stiffness. In more detail, the reading of hammer numbers less than 2 corresponds to compaction of less than 75%, while the reading of hammer numbers greater than 3 in the vertical and 2.94 in the horizontal directions on clay surfaces designates compaction of 90%.

Mesoscale computational modeling of concrete-like particle-reinforced composites with non-convex aggregates

This paper presents a novel mesoscale finite element model for predicting the effective mechanical properties of concrete-like particle-reinforced composites with concave aggregates. In the mesoscale model, unit cells (UC) with randomly distributed non-convex particles and period boundaries are generated through computationally efficient algorithms to represent the periodic microstructures of concrete composites. Numerical homogenization is performed to calculate the effective mechanical parameters based on an unsorted node set technique. The results predicted by the proposed model show good agreement with the experimental measurements. The parametric study also indicates that UC models with periodic placement of particles at the boarders yield higher elastic modulus compared with those without periodic boundary particle placement, and the influence of boarder particles on homogenized material properties decreases as the UC size increases. Moreover, computational studies show that the elastic moduli of composites consisting of concavity particles are larger than those with the round and smooth particles given the same particle volume fraction. The proposed mesoscale modeling approach can serve as an easy and fast tool in assisting the design and optimization of strong, light-weight and reliable particle-reinforced composites.

Numerical modeling of the stress state of constructions from fibrous composites

The paper is devoted to numerical modeling of the deformed state of physically nonlinear transversely isotropic bodies with an aperture. To solve the problem of the theory of plasticity, a simplified theory of small elastoplastic deformations for a transversely isotropic body is used. In work, to describe the anisotropy of the mechanical properties of transversely isotropic materials, a structural-phenomenological model is used. It allows you to represent the source material in the form of a complex of two jointly working isotropic materials. The main material is considered from the standpoint of continuum mechanics. The fiber material is oriented along the anisotropy direction of the starting material. It is assumed that the fibers perceive only the axial tensile-compression forces and are deformed together with the main material. The presentation of fibrous composites in the form of homogeneous anisotropic materials with effective mechanical parameters allows a fairly accurate calculation of structures with stress concentrators. Based on a simplified theory and finite element method, a computer model of nonlinear deformation of fibrous composites is constructed. The influence of the configuration of holes and a rectangular crack on the distribution of deformation and stress fields in the vicinity of these concentrators is investigated.

Fatigue properties of aluminium triangular lattice plates

We propose a method to predict the fatigue life of triangular lattices by using fatigue data from tests on single lattice struts. The method was validated using fatigue tests on 6 identical triangular lattice plates divided into three groups with different initial crack lengths. The predicted fatigue lives of lattices agree very well with the experimental results. A three-stage mechanism of lattice fatigue was observed in the tests, and the crack propagated in the direction 30° to the horizontal axis in the upper half of lattice plate in all three groups. The fatigue crack propagation rate was also studied and calculated by using the effective mechanical parameters from the homogenized structure. Experimental fatigue crack growth rate data were compared with predictions, showing that the proposed method can also predict the crack growth rate in triangular lattices very well.

Computer simulation of damage to metal-ceramic composites under shock loading

In this work the results of studying of the mechanical behaviour of metal-ceramic composites with an aluminium matrix on mesoscale level are submitted. Computer simulation of mechanical reaction of representative volume of composite material, considered as ensemble of the interacting structural elements (ceramic particles and metal matrix), is used for studying processes of the nucleation and growth of damages on mesoscale level of metal-ceramic composites under the loading by shock pulses. The sizes of representative volume give the possibilities to enter effective mechanical parameters of a composite material. The mechanical behaviour of aluminium matrix is described by the model of the damaged elastic-plastic medium. The model of the damaged brittle solid is used for ceramics. The problem is solved in 2D statement with application of finite-difference method. The results of computer simulation show that the local tensile stresses can appear in unloading wave and can cause damages in ceramic particles. In the region of composite where two opposing unloading waves interacts (spall zone) the calculation predicts the existence of cracked ceramic particles, local damages in metal matrix and existence of mesoscale and macro-scale cracks.

In Vivo Force Application Reveals a Fast Tissue Softening and External Friction Increase during Early Embryogenesis

SummaryDuring development, cell-generated forces induce tissue-scale deformations to shape the organism [1, 2]. The pattern and extent of these deformations depend not solely on the temporal and spatial profile of the generated force fields but also on the mechanical properties of the tissues that the forces act on. It is thus conceivable that, much like the cell-generated forces, the mechanical properties of tissues are modulated during development in order to drive morphogenesis toward specific developmental endpoints. Although many approaches have recently emerged to assess effective mechanical parameters of tissues [3, 4, 5, 6, 7, 8], they could not quantitatively relate spatially localized force induction to tissue-scale deformations in vivo. Here, we present a method that overcomes this limitation. Our approach is based on the application of controlled forces on a single microparticle embedded in an individual cell of an embryo. Combining measurements of bead displacement with the analysis of induced deformation fields in a continuum mechanics framework, we quantify material properties of the tissue and follow their changes over time. In particular, we uncover a rapid change in tissue response occurring during Drosophila cellularization, resulting from a softening of the blastoderm and an increase of external friction. We find that the microtubule cytoskeleton is a major contributor to epithelial mechanics at this stage. We identify developmentally controlled modulations in perivitelline spacing that can account for the changes in friction. Overall, our method allows for the measurement of key mechanical parameters governing tissue-scale deformations and flows occurring during morphogenesis.

Computer modeling of deformed state of physically non-linear transversal-isotropic bodies with hole

The paper presents computer simulation of the deformed state of physically nonlinear transversally isotropic bodies with hole. To describe the anisotropy of the mechanical properties of transversally isotropic materials a structurally phenomenological model is used. This model allows to represent the initial material in the form of two co-operating isotropic materials: the basic material (binder) considered from the positions of continuum mechanics and the fiber material oriented along the anisotropy direction of the original material. It is assumed that the fibers perceive only the axial tensile-compression forces and are deformed together with the base material. To solve the problem of plasticity, a simplified deformation theory of small elastic-plastic deformations for a transversely isotropic body, proposed by prof. Pobedrey B.E., is used. A simplified theory allows to apply the theory of small elastic-plastic deformations to solve specific applied problems, since in this case the fibrous medium is replaced by an equivalent transversely isotropic medium with effective mechanical parameters. The essence of simplification is that with simple stretching of composite in direction of the transversal isotropy axis and in direction perpendicular to it, plastic deformations do not arise. As a result, the intensity of stresses and deformations both along the principal axis of the transversal isotropy and along the perpendicular plane of isotropy is determined separately. The representation of fibrous composites in the form of homogeneous anisotropic materials with effective mechanical parameters makes it possible to make a fairly accurate calculation of stresses and deformations. The calculation is carried out under different loading conditions, bearing in mind that both sizes characterizing the fibrous material-the fiber thickness and the gap between the fibers-are several orders smaller than the radius of the hole. Based on the simplified theory and the finite element method, a computer model of nonlinear deformation of fibrous composites is constructed. For carrying out computational experiments, a specialized software package was developed, the effect of hole configuration on the distribution of deformation and stress fields in the vicinity of concentrators was investigated.

Researches of mechanical behavior of bone tissues for development and selection of individual ceramic implants

The researches of mechanical behavior were conducted and the effective mechanical properties of model compact bone micro volumes under uniaxial compression were obtained taking into account the structural characteristics and the mineral content; experimental analysis of the mechanical behavior and the effective mechanical parameters of obtained porous zirconia ceramics were conducted. The comparison of obtained in paper calculated and experimental mechanical properties of bone and ceramics was carry out and the recommendations on the use the ceramics with certain porosity to replace the compact bone fragment with a certain structure and mineral content were suggested.

Study of Bone Tissue Stress and Strain State Aimed at Development of Intelligent Biomaterials for Osteoimplantation

This article studies the stress and strain state of simulated microvolumes of compact bone tissue under uniaxial compression, having different orientation of collagen-mineral fibers, different porosity and mineral content. The purpose of the study is to work out recommendations on development of artificial mechanically compatible biomaterials for osteoimplants. It has been found out that it is necessary to take into account the effective mechanical parameters defining the distribution of the bone tissue stress and strain when making individual implants.

Numerical simulation of elastic-plastic stress concentration in fibrous composites

In the present study an elastic-plastic strain analysis is carried out for fibrous composites by using numerical modeling. Application of homogeneous transversely-isotropic model was chosen based on problem solution of a square plate with a circular hole under uniaxial tension. The results obtained in this study correspond to the solution of fiber model trial problem, as well as to analytical solution. Further, numerical algorithm and software has been developed, based on simplified theory of small elastic strains for transversely-isotropic bodies, and FEM. The influence of holes and cracks on stress state of complicated configuration transversely-isotropic bodies has been studied. Strain curves and plasticity zones that are formed in vicinity of the concentrators has been provided. Numerical values of effective mechanical parameters calculated for unidirectional composites at different ratios of fiber volume content and matrix. Content volume proportions of fibers and matrix defined for fibrous composite material that enables to behave as elastic-plastic body or as a brittle material. The influences of the fibrous structure on stress concentration in vicinity of holes on boron/aluminum D16, used as an example.

Coupled Hydro-mechanical Processes Associated with Multiphase Flow in a Dual-continuum System: Formulations and an Application

Fractured rock has often been conceptualized as a dual-continuum system for many practical applications. This study proposes a systematic approach to deal with multiphase flow in a dual-continuum system. Considering that fluid flow occurs in pore volumes (including fracture apertures), we first develop a so-called pore-space conservation equation for deformed fractured rock and then combine this equation with fluid mass balance to derive governing equations for multiphase flow associated with rock deformation. Constitutive relationships are also presented for describing stress dependence of hydraulic properties and effective mechanical parameters for bulk rock body (as a function of the corresponding parameters for fracture and matrix continua). Finally, we applied the developed approach to a CO2 geological sequestration problem to demonstrate the usefulness of the approach.

Bearing strength prediction for reinforced composite laminates for cryogenic and aerospace applications

The procedures of bearing strength prediction for composite laminates reinforced with high-strength unidirectional fibers at room and cryogenic temperatures are discussed. The best agreement between the calculated and experimental data is observed when the temperature dependence of effective mechanical parameters of plies is allowed for within the framework of the elastic theory of laminated heterogeneous bodies.