Showing papers on "Material properties published in 2020"

Microstructure and mechanical properties of 316L austenitic stainless steel processed by different SLM devices

Abstract: In this work, we examined the influence of different types of selective laser melting (SLM) devices on the microstructure and the associated material properties of austenitic 316L stainless steel. Specimens were built using powder from the same powder batch on four different SLM machines. For the specimen build-up, optimized parameter sets were used, as provided by the manufacturers for each individual SLM machine. The resulting microstructure was investigated by means of scanning electron microscopy, which revealed that the different samples possess similar microstructures. Differences between the microstructures were found in terms of porosity, which significantly influences the material properties. Additionally, the build-up direction of the specimens was found to have a strong influence on the mechanical properties. Thus, the defect density defines the material’s properties so that the ascertained characteristic values were used to determine a Weibull modulus for the corresponding values in dependence on the build-up direction. Based on these findings, characteristic averages of the mechanical properties were determined for the SLM-manufactured samples, which can subsequently be used as reference parameters for designing industrially manufactured components.

Effect of build thickness and geometry on quasi-static and fatigue behavior of Ti-6Al-4V produced by Electron Beam Melting

Abstract: The geometry and material properties of additively manufactured (AM) parts are closely related in a way that any alteration in geometry of the part will change the underlying manufacturing strategy This in turn, affects the microstructure and consequently, the mechanical behavior of material This paper aims to evaluate the effect of the AM part’s thickness and geometry on microstructure, surface roughness, and mechanical properties under quasi-static and fatigue loading conditions by performing experimental tests A series of Ti-6Al-4V specimens with three different thicknesses and two different geometries were fabricated using electron beam melting (EBM) The results of microstructural analyses revealed that specimens with lower build thickness experience finer grain size, higher microhardness, and lower elongation at failure Although the microstructure of the produced parts was strongly affected by the build thickness, different surface to volume ratios eliminated the effect of microstructural differences and governed the fatigue properties of the parts The size effect on the microstructural features, geometrical appearance, mechanical properties of the AM parts should be considered for the design and failure analysis of complex structures

Isogeometric nonlinear transient analysis of porous FGM plates subjected to hygro-thermo-mechanical loads

Abstract: To provide reference solutions and results for structural and material design, nonlinear transient responses of porous functionally graded plate (PFGM) in hygro-thermo-mechanical environments are studied. Two different porous distributions through the thickness are considered. The material properties such as Young's modulus, Poisson's ratio and thermal conductivity are computed by a modified power law. The hygro-thermal effects are considered as nonlinear through the thickness of the plate. The geometrically nonlinear transient behaviors are expressed by adopting the von Karman relations and solved by Newmark time integration scheme. Based on a combination between the third-order shear deformation theory (TSDT) and isogeometric analysis (IGA), discretize governing equations are approximated. These approaches achieve naturally any desired degree of continuity of basis functions, so that they are easy to fulfil the C1-continuity requirement of the plate model. The formulations take into account the transverse shear deformation and account for the material properties at elevated moisture concentrations and temperature. The effects played by the moisture concentration, temperature rise, porous volume fraction, boundary conditions and thickness-to-length ratio are performed and results illustrate interesting dynamic phenomenon for PFGM in hygro-thermo-mechanical environments. With obtained results, the nonlinear characteristics of the proposed structure with porosities are based on physical parameters.

Microstructurally-guided explicit continuum models for isotropic magnetorheological elastomers with iron particles

Abstract: This work provides a family of explicit phenomenological models both in the F − H and F − B variable space. These models are derived directly from an analytical implicit homogenization model for isotropic magnetorheological elastomers (MREs), which, in turn, is assessed via full-field numerical simulations. The proposed phenomenological models are constructed so that they recover the same purely mechanical, initial and saturation magnetization and initial magnetostriction response of the analytical homogenization model for all sets of material parameters, such as the particle volume fraction and the material properties of the constituents (e.g., the matrix shear modulus, the magnetic susceptibility and magnetization saturation of the particles). The functional form of the proposed phenomenological models is based on simple energy functions with small number of calibration parameters thus allowing for the description of magnetoelastic solids more generally such as anisotropic (with particle-chains) ones, polymers comprising ferrofluid particles or particle clusters. This, in turn, makes them suitable to probe a large set of experimental or numerical results. The models of the present study show that in isotropic MREs, the entire magnetization response is insensitive to the shear modulus of the matrix material even when the latter ranges between 0.003- 0 . 3 MPa , while the magnetostriction response is extremely sensitive to the mechanical properties of the matrix material.

Nonlinear vibration analysis of fiber reinforced composite cylindrical shells with partial constrained layer damping treatment

Abstract: This research proposes a novel analytical model capable of accurately predicting the strain-dependent characteristics of fiber reinforced composite shells (FRCSs) with partial constrained layer damping (CLD) treatment by considering the nonlinearities of fiber reinforced composite and viscoelastic materials simultaneously. The nonlinear material properties are represented based on Jones-Nelson nonlinear theory, energy-based strain energy method, and complex modulus method. Then, the governing equations of motion for FRCSs are developed via Ritz method, and the identification procedure of nonlinear fitting parameters is also presented. By taking a T300 carbon fiber/epoxy resin cylindrical shell with partial CLD patches as an example, a series of experiments are carried out to validate the proposed modeling approach. Finally, the effects of material properties on nonlinear vibration behaviors of FRCSs covered with partial CLD patches are evaluated. Comparisons show that the proposed nonlinear model is more accuracy than that without considering strain dependence, where the maximum errors between the proposed model and measured data for natural frequencies, damping ratios and resonant response are 6.9%, 11.3%, and 11.2%, respectively.

Numerical Modelling of concrete-to-UHPC Bond Strength

Abstract: Ultra-High Performance Concrete (UHPC) has been a material of interest for retrofitting reinforced concrete elements because of its pioneer mechanical and material properties. Numerous experimental studies for retrofitting concrete structures have shown an improvement in durability performance and structural behaviour. However, conservative and sometimes erroneous estimates for bond strength are used for numerically calculating the strength of the composite members. In addition, different roughening methods have been used to improve the bond mechanism; however, there is a lack of numerical simulation for the force transfer mechanism between the concrete substrate and UHPC as a repair material. This paper presents an experimental and numerical programme designed to characterize the interfacial properties of concrete substrate and its effect on the bond strength between the two materials. The experimental programme evaluates the bond strength between the concrete substrates and UHPC with two different surface preparations while using bi-surface test and additional material tests, including cylinder and cube tests for compression property, direct tension test, and flexural test to complement UHPC tensile properties. Non-linear finite element analysis was conducted, which uses a numerical zero thickness volume model to define the interface bond instead of a traditional fixed contact model. The numerical results from the zero thickness volume model show good agreement with the experimental results with a reduction in error by 181% and 24% for smooth and rough interface surfaces if compared to the results from the model with a fixed contact.

Modeling of thermal behavior and microstructure evolution during laser cladding of AlSi10Mg alloys

Abstract: An improved three-dimensional finite element model has been proposed for studying the thermal behavior and microstructure evolution during laser cladding of AlSi10Mg alloys. Different material properties between AlSi10Mg powders and AlSi10Mg alloys are distinguished from the experiment and theoretical calculation to provide more reliable material parameters for simulation. In order to investigate the melting and solidification process during the formation of cladding layers, a temperature selection judgment mechanism is established to simulate the evolution of AlSi10Mg powders from the powder state to melting state and alloy state. In addition, to simulate the complex thermal behavior associated with powder particles and the voids between particles, a simplified exponential attenuation model is used for correcting the heat source. A complex asymmetric heat source considering about the different material properties and laser absorptivity on both sides of the remelting zone is used for multi-track cladding process. By simulating the temperature distribution of molten pool, the improved FEM could be used to predict the geometric shape of cladding layers (ignoring the effect of melting flow) and the temperature history. The simulation results show that the heat tends to diffuse to the unmelted powder owing to the asymmetric heat source during multi-track cladding, which leads to the asymmetry of cladding layers along the width direction. Based on the results of the temperature field simulations and the solidification characteristics of AlSi10Mg powders, the temperature gradient (G), solidification growth rate (R), cooling rate (G*R) and G/R are investigated to predict the morphology and size of the solidification microstructure under different laser scanning parameters. The scanning speed mainly determines the cooling rate during the laser cladding process, which results in different microstructures. Higher scanning speed leads to higher cooling rate, corresponding to a finer microstructure. Coarse dendrites are generated at the bottom of the molten pool, while finer dendrites are formed at the top.

Interlayer bonding has bulk-material strength in extrusion additive manufacturing: New understanding of anisotropy

Abstract: This study demonstrates that the interface between layers in 3D-printed polylactide has strength of the bulk filament. Specially designed 3D-printed tensile specimens were developed to test mechanical properties in the direction of the extruded filament (F specimens), representing bulk material properties, and normal to the interface between 3D-printed layers (Z specimens). A wide range of cross-sectional aspect ratios for extruded-filament geometries were considered by printing with five different layer heights and five different extruded-filament widths. Both F and Z specimens demonstrated bulk material strength. In contrast, strain-at-fracture, specific load-bearing capacity, and toughness were found to be lower in Z specimens due to the presence of filament-scale geometric features (grooves between extruded filaments). The different trends for strength as compared to other mechanical properties were evaluated with finite-element analysis. It was found that anisotropy was caused by the extruded-filament geometry and localised strain (as opposed to assumed incomplete bonding of the polymer across the interlayer interface). Additionally, effects of variation in print speed and layer time were studied and found to have no influence on interlayer bond strength. The relevance of the results to other materials, toolpath design, industrial applications, and future research is discussed. The potential to use this new understanding to interpret historic and future research studies is also demonstrated.

Photo-Thermal-Elastic Interaction in a Functionally Graded Material (FGM) and Magnetic Field

Abstract: In this work, we aim to investigate the photo-thermal-elastic waves interaction in a nano-composite semiconductor, elastic and functionally graded material (FGM). The governing equations are taken in one dimension during the influence of initial magnetic field when the elastic medium is isotropic and the material properties are non-homogeneity. In the domain of Laplace transform the basic equations in non- dimensional forms are formulated in a vector matrix differential equation and are solved by the eigenvalue and eigenvector approach. The physical quantities are obtained by applying the numerical inversion method of the transforms. The numerical results of the physical quantities (carrier density, displacement, temperature, stresses and strains) are discussed and illustrated graphically.

Free vibrations and static analysis of functionally graded sandwich plates with three-dimensional finite elements

Abstract: A three-dimensional modelling of free vibrations and static response of functionally graded material (FGM) sandwich plates is presented. Natural frequencies and associated mode shapes as well as displacements and stresses are determined by using the finite element method within the ABAQUS™ code. The three-dimensional (3-D) brick graded finite element is programmed and incorporated into the code via the user-defined material subroutine UMAT. The results of modal and static analyses are demonstrated for square metal-ceramic functionally graded simply supported plates with a power-law through-the-thickness variation of the volume fraction of the ceramic constituent. The through-the-thickness distribution of effective material properties at a point are defined based on the Mori-Tanaka scheme. First, exact values of displacements, stresses and natural frequencies available for FGM sandwich plates in the literature are used to verify the performance and estimate the accuracy of the developed 3-D graded finite element. Then, parametric studies are carried out for the frequency analysis by varying the volume fraction profile and value of the ceramic volume fraction.

Thermo-elastic buckling and post-buckling analysis of functionally graded thin plate and shell structures

Abstract: In this paper, we extend the Kirchhoff–Love model to thermal buckling and post-buckling analysis of functionally graded structures. The kernel idea of the proposed model consists of the consideration of large displacements and finite rotation to accurately model the thermal effects on buckling and post-buckling behavior of such structures. Both uniform and nonuniform temperature distributions are considered. Material properties of the FG structures are graded in the thickness direction and assumed to obey a power law distribution of the volume fraction of the constituents. The effectiveness and usefulness of the proposed model are highlighted through different numerical examples, and the effects of the volume fraction exponent, thermal loads, length-to-thickness ratio, boundary conditions and geometrical parameters on the buckling and post-buckling behavior of FGM structures are also examined.

Study on variations of microstructure and metallurgical properties in various heat-affected zones of SLM fabricated Nickel–Titanium alloy

Abstract: Nickel–Titanium (NiTi) is a material of great interest in modern industry as its shape memory and superelastic behaviors provide unique and useful properties that can be incorporated into complex designs and applications. However, due to its poor machinability, it is difficult to realize its full potential with conventional manufacturing techniques. With the advent of additive manufacturing, the potential for the use of NiTi in modern designs has been reignited and the analysis and optimization of its mechanical properties are a pivotal point of current material science research. Furthermore, insight into the variations of these material properties and how they vary throughout an additively manufactured part is key to improving the quality and repeatability of these parts. In this research paper, samples are printed using a single set of process parameters. These samples are then cut and analyzed for grain structure, chemical composition, microstructure, and hardness. Finally, results are reported and variations in these material properties are summarized.

Free vibration analysis of smart laminated carbon nanotube-reinforced composite cylindrical shells with various boundary conditions in hygrothermal environments

Abstract: Free vibration analysis is carried out for piezoelectric coupled carbon nanotube (CNT)-reinforced composite cylindrical shells with the influences of various boundary conditions and hygrothermal environmental conditions for the first time. A simple and effective non-iterative mathematical method is used to calculate the natural frequencies. The equilibrium equations of motion are obtained based on the first-order shear deformation shell theory with the coupling effects of piezoelectricity, temperature, and moisture, respectively based on the Maxwell equation, the Fourier heat conduction equation, and the Fickian moisture diffusion equation. The Mori-Tanaka micromechanics model is used to estimate the resulting material properties for a composite shell reinforced with CNTs. Presented methodology and attained results are validated with the existing results in the literature. The effects of the boundary conditions, lamination stacking sequence, volume fraction and orientation of CNTs, piezoelectricity, and geometry of the shell on the natural frequencies of the shell are investigated. A moderate effect of temperature/moisture variation on the natural frequencies is also observed. It is found that the influence of structural boundary conditions is more significant at higher CNT volume fractions and for thicker and shorter shells, and the piezoelectricity effect is more obvious at higher circumferential mode. The model and results presented in this study can be utilized to determine vibration characteristics of smart CNT-reinforced composites subjected to hygrothermal loading as well as mechanical loading.

Estimating Powder-Polymer Material Properties Used in Design for Metal Fused Filament Fabrication (DfMF 3 )

Abstract: Metal fused filament fabrication (MF3) combines fused filament fabrication and sintering processes to fabricate complex metal components. In MF3, powder-polymer mixtures are printed to produce green parts that are subsequently debound and sintered. In the design for MF3 (DfMF3), it is important to understand how material properties of the filament affect processability, part quality, and ensuing properties. However, the materials property database of powder-polymer materials to perform DfMF3 simulations is very limited, and experimental measurements can be expensive and time-consuming. This work investigates models that can predict the powder-polymer material properties that are required as input parameters for simulating the MF3 using the Digimat-AM® process design platform for fused filament fabrication. Ti-6Al-4V alloy (56–60 vol.%) and a multicomponent polymer binder were used to predict properties such as density, specific heat, thermal conductivity, Young’s modulus, and viscosity. The estimated material properties were used to conduct DfMF3 simulations to understand material-processing-geometry interactions.

Numerical study of the impact of vaporisation on melt pool dynamics in Laser Powder Bed Fusion - Application to IN718 and Ti-6Al-4V

Abstract: A finite element model of Laser Powder Bed Fusion (LPBF) process applied to metallic alloys at a mesoscopic scale is presented. This Level-Set model allows to follow melt pool evolution and track development during building. A volume heat source model is used for laser/powder interaction considering the material absorption coefficients, while a surface heat source is used to consider the high laser energy absorption by dense metal alloys. An energy solver is applied considering convection and conductivity evolution in the system. Shrinkage during consolidation from powder to dense material is modelled by a compressible Newtonian constitutive law. An automatic remeshing strategy is also used to provide a good compromise between accuracy and computing time. Different cases are investigated to demonstrate the influence of the vaporisation phenomena, of material properties and of laser scan strategy on bead morphology.