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research-article  
Alireza Bayat and Faramarz Gordaninejad
J. Eng. Mater. Technol   doi: 10.1115/1.4037023
A scale-dependent numerical approach is developed through combining the finite element-based averaging process with the Monte-Carlo method to determine the desired size of a characteristic volume element for a random magnetoactive composite under applied magnetic field and large deformations. Spatially random distribution of identically magnetic inclusions inside a soft homogeneous matrix is considered to find the appropriate size of the characteristic volume element. Monte-Carlo method is used to generate ensembles of a randomly distributed magnetoactive composite to be applied in the homogenization study. The ensemble is utilized as a statistical volume element in a scale dependent numerical algorithm to search the desired characteristic volume element size. Results of this study can be used to investigate effective behavior and multi-scale modeling of randomly particulate magnetoactive composites.
TOPICS: Composite materials, Particulate matter, Magnetic fields, Algorithms, Multiscale modeling, Deformation
research-article  
Audrey Gbgaguidi, Sirish Namilae and Daewon Kim
J. Eng. Mater. Technol   doi: 10.1115/1.4037024
Hybrid nanocomposites with multiple fillers like carbon nanotubes (CNT) and graphene nanoplatelets (GNP) are known to exhibit improved electrical and electromechanical performance when compared to mono-filler composites. We developed a two dimensional Monte Carlo percolation network model for hybrid nanocomposite with CNT and GNP fillers and utilized it to study the electrical conductivity and piezoresistivity as a function of nanocomposite microstructural variations. The filler intersections are modeled considering electron tunneling as the mechanism for electrical percolation. Network modification after elastic deformation is utilized to model the nanocomposite piezoresistive behavior. Systematic improvement in percolation threshold, electrical conductivity and piezoresistivity were observed in the hybrid nanocomposites, compared to mono-filler CNT nanocomposites. Parametric studies have been performed to show the effect of the GNP content, size, aspect ratio and alignment on the conductivity and piezoresistivity of hybrid CNT-GNP polymer composites.
TOPICS: Nanocomposites, Fillers (Materials), Carbon nanotubes, Electrical conductivity, Percolation theory, Network models, Deformation, Electrons, Composite materials, Graphene, Polymer composites, Tunnel construction
research-article  
Chetan P Nikhare, Emmett Vorisek, John R. Nolan and John T. Roth
J. Eng. Mater. Technol   doi: 10.1115/1.4037020
Traditionally, the mechanical properties of materials have been characterized using the uniaxial tension test. This test is considered adequate for simple forming operations where single axis loading is dominant. Previous studies, however, have noted that the data acquired from this type of testing is not enough and additional details in other axes under simultaneous deformation conditions are important. To analyze the biaxial strain, some studies have suggested using the limiting dome height test and bulge test. However, these tests limit the extent of using multi-axial loading and the resulting stress pattern due to contact surfaces. Therefore, researchers devised the biaxial machine which is designed specifically to provide biaxial stress components using multiple and varying loading conditions. The idea of this work is to evaluate the relationship between the dome test data and the biaxial test data. For this comparison, cruciform specimens with a diamond shaped thinner gage in the center were deformed with biaxial stretching on the biaxial testing machine. In addition, the cruciform specimens were bi-axially stretched with a hemispherical punch in a conventional die-punch setting. Furthermore, in each case, the process was simulated using a 3D model generated on ABAQUS. These models were then compared with the experimental results. The forces on each arm, strain path, forming and formability was analyzed. The differences between the processes were detailed. It was found that biaxial tests eliminated the pressurization effect which could be found in hemispherical dome tests.
TOPICS: Domes (Structural elements), Tension, Forming limit diagrams, Testing, Stress, Machinery, Gages, Mechanical properties, Diamonds, Diluents, Three-dimensional models, Deformation
research-article  
Salah U. Hamim and Raman P. Singh
J. Eng. Mater. Technol   doi: 10.1115/1.4037022
This study explores the application of a Proper Orthogonal Decomposition (POD) and Radial Basis Function (RBF)- based surrogate model to identify parameters of a nonlinear viscoelastic material model using nanoindentation data. The inverse problem is solved by reducing the difference between finite element simulation-trained surrogate model approximation and experimental data through genetic algorithm- based optimization. The surrogate model, created using POD-RBF, is trained using FE data obtained by varying model parameters within a parametric space. Sensitivity of the model parameters towards the load-displacement output is utilized to reduce the number of training points required for surrogate model training. The effect of friction on simulated load-displacement data is also analyzed. For the obtained model parameter set, the simulated output matches well with experimental data for various experimental conditions.
TOPICS: Nanoindentation, Stress, Displacement, Inverse problems, Friction, Simulation, Viscoelastic materials, Algorithms, Finite element analysis, Optimization, Approximation, Principal component analysis
research-article  
Xiaodong Li, Ying Chang, Cunyu Wang, Shuo Han, Daxin Ren, Ping Hu and Han Dong
J. Eng. Mater. Technol   doi: 10.1115/1.4037017
With the development of the automotive industry, the application of the high strength steel becomes an effective way to improve the lightweight and safety. In this paper, the third-generation automotive medium-Mn steel (TAMM steel) is studied. The warm-stamped TAMM steel holds the complete and fine-grained martensitic microstructure without decarbonization layer, which contributes to high and well-balanced mechanical properties. Furthermore, the martensitic transformation mechanism of the TAMM steel are investigated by the dilatation tests. The results indicate that the effects of the loading method on the Ms temperature under different loads are different. The Ms temperature is hardly influenced under the tensile loads and low compressive load. However, it is slightly decreased under the high compressive load. Moreover, the effects of the strain and strain rate on the Ms temperature are insignificant and can be neglected. As a result, this research proves that the martensitic transformation of the TAMM steel is rarely influenced by the process parameters, such as stamping temperature, loading method, load, strain and strain rate. The actual stamping process can be designed and controlled accurately referring to the CCT curves to realize the required properties and improve the formability of the automotive part.
TOPICS: Steel, Martensitic transformations, Stress, Temperature, Metal stamping, Mechanical properties, Automotive industry, Safety, High strength steel
research-article  
Renan L. Ribeiro and Michael R. Hill
J. Eng. Mater. Technol   doi: 10.1115/1.4037021
Cold expansion (CX) is a material processing technique that has been widely used in the aircraft industry to enhance fatigue life of structural components containing holes. CX introduces compressive hoop residual stresses that slow crack growth near the hole edge. The objective of this paper is to predict residual stresses arising from cold expansion using two different finite element (FE) approaches, and compare the results to measurement data obtained by the contour method. The paper considers single-hole, double-hole, and triple-hole configurations with three different edge margins. The first FE approach considers process modeling, and includes elastic-plastic behavior, while the second approach is based on the eigenstrain method, and includes only elastic behavior. The results obtained from the FE models are in good agreement with one another, and with measurement data, especially close to the holes, and with respect to the effect of edge margin on the residual stress distributions. The distribution of the residual stress and equivalent plastic strain around the holes is also explored, and the results are discussed in detail. The eigenstrain method was found to be very useful, providing generally accurate predictions of residual stress.
TOPICS: Stress, Fasteners, Modeling, Finite element analysis, Residual stresses, Materials processing, Aircraft, Fatigue life, Finite element model, Fracture (Materials), Elasticity, Structural elements (Construction)

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