Numerically predicted high cycle fatigue properties through representative volume elements of the microstructure

Towards a faster determination of high cycle fatigue properties taking into account the influence of a plastic pre-strain from selfheating measurements

Evolution of elliptic-cylindrical and circular-cylindrical voids inside power-law viscous solids

In this study, a numerical representative volume element (RVE) model was used to predict the mechanical properties of a Rice Husk Particulate (RHP)-Epoxy composite for use as an alternative material in non-critical applications. Seven different analytical models Counto, Ishai-Cohen, Halpin-Tsai, Nielsen, Nicolais, Modified Nicolais and Pukanszky were used as comparison tools for the numerical model. The mechanical properties estimated for 0%, 10% and 30% RHP-Epoxy composites using the numerical and analytical models are in general agreement with each other. Using the analytical models, it was calculated that an increase in volume percentage of RHP to 30% led to continual reduction in elastic Young’s modulus and ultimate tensile strength of the composite. The numerical RVE models also predicted a similar trend between filler volume percentage and material properties. Overall, the results of this study suggest that RHP can be used to reduce the composite raw material costs by replacing the more expensive polymer content with agricultural waste products with limited compromise to the composite’s mechanical properties.

Purpose The purpose of this study to analyze the plastic anisotropy of 6061 aluminum alloy with finite deformation using crystal plasticity finite element method. Design/methodology/approach A representative volume element (RVE) model was constructed by Voronoi tessellation. In this model, grain shapes, grain orientations and distribution of grains were involved. The mechanical response of the component under composite loading was tested using specify cruciform specimen. Moreover, different stress and strain states in the specific central region were analyzed to reveal the effects of complex loading. Findings We calculated the influence of misorientation of adjacent grains as well as the evolution of the micro structure’s plastic deformation on the macroscopic deformation of the structure. Geometry design for the cruciform specimen helps obtain a homogenous distribution of the stress and strain at the specimen center. In this process, the initial grain orientation is also an important factor, and the larger misorientations between special grains may cause greater stress concentration. Originality/value The influence of micro-scale factors on macro-scale plastic anisotropy of AA6061 is analyzed using RVE model and cruciform specimen, and they offer a reference for related research.

Modeling of frontal polymerization of carbon fiber and dicyclopentadiene woven composites with stochastic material uncertainty

The present article is focused on the in-house synthesis of graphene nano-flakes (size range: 3–8 nm) reinforced Al-alloy (AA6005 series) nanocomposites using stir casting process. The microstructure of the obtained Al nanocomposites at different concentration of flake shaped graphene nanoparticles (GRNPs) show that the particles at 2 wt% and 4 wt% found to be distributed extensively on the surfaces of Al alloy matrix but observed negligible across the grain boundary whereas in the case of 6 wt% concentrated developed composite specimen, the GRNPs were observed to be well dispersed both on the surfaces and grain boundary of the matrix. With the addition of the particles, there found to be the formation of more voids in the nanocomposite specimens. The experimental characterization results reveal that with the increase in graphene content to 6 wt%, the tensile strength, compressive strength, impact energy, hardness and wear resistance of the nanocomposites were increased by 9% to 36%, 30% to 44%, 9.8 J, 36.03 HRB and 33% respectively as compared to unreinforced alloy. It was observed that the composites with increased concentration of reinforcement exhibits brittle behaviour and at 6 wt% GRNPs, the elongation is almost found to be 50% lower than the unreinforced one. Further, a 3D microstructure representative volume element (RVE) model of aluminium nanocomposite is generated using Digimat-FE software. Then, microstructural deformation behaviour of the nanocomposite is realized by RVE model. The simulation results reveal that the tensile property of the aluminium nanocomposites predicted using RVE model is in well agreement with the experimental values.

In this work, three-dimensional (3D) finite element simulations were undertaken to study the effects of lightning strikes on the microscale behaviour of continuous fibre-reinforced composite materials and to predict and understand complex lightning damage mechanisms. This approach is different from the conventional mesoscale or macroscale level of analysis, that predicts the overall lightning damage in composite laminates, thus providing better understanding of lightning-induced thermo-mechanical damage at a fundamental level. Micromechanical representative volume element (RVE) models of a UD composite laminate were created with circular carbon fibres randomly distributed in an epoxy matrix. The effects of various grounding conditions (one-, two-, and four-side grounding), fibre volume fractions ( V f = 55, 60%, and 65%), and peak current amplitudes (10, 20, and 40 kA) on microscopic damage in RVE models were characterised to understand fibre, epoxy matrix, and fibre-matrix interfacial damage associated with a lightning strike. Thermal damage, estimated based on epoxy matrix decomposition temperature, was largely constant up to 20 kA before increasing significantly at 40 kA. Severe thermal damage steadily decreased with increasing V f. Thermo-mechanical damage was predicted using a ductile plasticity model with Drucker–Prager yield criterion for epoxy matrix failure, and cohesive surfaces for fibre-matrix interface debonding. Thermal strain had the largest contribution to thermo-mechanical damage, while dynamic pressure loading was negligible in all RVE models. The RVE model proposed in this work, to the best of the authors’ knowledge, is the first model predicting lightning-induced fibre-matrix interfacial damage.

ABSTRACTWe report a method, named as T & A treatment, to improve the high-cycle fatigue (HCF) property of twinning-induced plasticity (TWIP) steel without sacrificing its ductility and work-hardening ability. A long-range gradient in grain size was obtained in the TWIP steel, whose HCF resistance is better than both coarse-grain and fine-grain steels, breaking the rule of mixture. The surprising HCF property of the graded grain structure is believed to originate from the large generation of geometrically necessary dislocations and the formation of hard core and soft shell construction during cyclic loading.

Analysis of meso-inhomogeneous deformation on a metal material surface under low-cycle fatigue

Heterogenous microstructures of High-Pressure Die-Casting (HPDC) Al–Si alloy lead to random strain concentrations during deformation. Different microstructural variations are considered, including Fe-rich phase and porosity, with focuses on different geometrical aspects. Representative Volume Element (RVE) models were established based on Electron Back Scatter Diffraction (EBSD) data using Finite Element Method (FEM). The effectiveness of the RVE models was verified by comparing predicted strain concentration locations with experimental results. The microstructural models were refined to explore effects of microstructural changes. The simulation results show that there is an interactive effect of porosity and Fe-rich phase on the microscopic strain field. When there is no porosity, the geometric properties of Fe-rich phase play an important role in changes of microscopic strain field. When average diameter of porosity is close to that of Fe-rich phase, position and shape of porosity dominate the microscopic strain field compared with that of Fe-rich phase.

Abstract

Crystal plasticity finite element (CPFEM) modeling of metals that can be age hardened consisting of second phase particles is extensively performed based on representative volume element (RVE) models. The RVE model is generated for ferritic low-carbon steel using the data obtained from microstructural observation through optical microscopy (OM) and electron backscatter diffraction (EBSD). The generated RVE is required to statistically represent the original material in terms of grain topology and texture in microscale, as well as the configuration of second phase particles in submicron scale. The multiscale, multi-phase nature of the generated RVE leads to a computationally expensive modeling procedure. To overcome this issue, an alternative multiscale modeling approach based on a homogenization scheme is proposed, in which the effect of second phase particles on deformation behavior is accounted for with no need for the explicit presence of particles in RVE. Lastly, a thorough parametric analysis is performed to investigate the sensitivity of the mechanical properties to the second phase particles in terms of size, volume fraction, geometrical distribution, and deformable or non-deformable properties of precipitates in the investigated material. The results show that the proposed multiscale modeling approach successfully accounts for the effect of second phase particles on deformation behavior, while the computational cost is reduced by more than 99%. In addition, the simulations show that the configuration of second phase particles at a microscale plays an important role in defining the mechanical behavior of the material.

Multiscale modeling: Prediction for thermophysical properties of needled carbon/carbon composite and evaluation of brake disk system

Multiscale modelling of stress and strain partitioning in Dual Phase (DP) steel was carried out using both realistic microstructure-based Representative Volume Element (RVE) models as well as stochastic microstructures generated by Monte Carlo (MC) method. The stochastic microstructure models were shown to resemble that of realistic microstructures, enabling research on the specific aspects of the microstructure that could be difficult to control and study during experimental work. One such feature of the realistic microstructures studied in this work was the grain size and microstructure morphology. The microstructures were generated with varying average grain sizes while all other parameters, such as boundary conditions, material properties and volume fractions of martensite and ferrite were kept constant. It is found that the effect of grain size is much more pronounced during the initial localisation of the plastic deformation at and around the interface of the phases. In addition, the decrease in ductility and increase in strength of the DP steels are directly related to the refinement of grain sizes of each phase and the stress-strain partitioning in between them.

The determination of high cycle fatigue (HCF) properties of a material with standard method requires a lot of specimens, and could be really time consuming. The self-heating method has been developed in order to predict S–N–P curves (i.e., amplitude stress – number of cycles to failure – probability of failure) with only a few specimens. So the time-saving advantage of this method has been demonstrated on several materials, at room temperature. In order to reduce the cost and time of fatigue characterization at high temperature, the self-heating method is adapted to characterize HCF properties of a titanium alloy, the Ti-6Al-4V (TA6V), at different temperatures. So the self-heating procedure is adjusted to conduct tests with a furnace. Two dissipative phenomena can be observed on self-heating curves. Because of this, a two-scale probabilistic model with two dissipative mechanisms is used to describe them. The first one is observed for low amplitudes of cyclic loading, under the fatigue limit, and the second one for higher amplitudes where the mechanisms of fatigue damage are activated and are dissipating more energy. This model was developed on steel at room temperature. Even so, it is used to describe the self-heating curves of the TA6V at several temperatures.