Accepted Manuscripts

Mehdi Ganjiani
J. Eng. Mater. Technol   doi: 10.1115/1.4037656
In this paper, an elastoplastic-damage constitutive model is presented. The formulation is cast within the framework of Continuum Damage Mechanics by means of the internal variable theory of thermodynamics. The damage is assumed as a tensor type variable and its evolution is developed based on the energy equivalence hypothesis. In order to discriminate the plastic and damage deformation, two surfaces named as plastic and damage are introduced. The damage surface has been developed so that it can model the nonlinear variation of damage. The details of the model besides its implicit integration algorithm are presented. The model is implemented as a user-defined subroutine UMAT in the Abaqus/Standard finite element program for numerical simulation purpose. In the regard of investigating the capability of model, the shear and tensile tests are experimentally conducted and corresponding results are compared with those predicted numerically. These comparisons are also accomplished for several experiments available in the literature. Satisfactory agreement between experiments and numerical predictions provided by the model implies the capability of the model to predict the plastic deformation as well as damage evolution in the materials.
TOPICS: Hardening, Damage, Deformation, Thermodynamics, Computer simulation, Shear (Mechanics), Tensors, Algorithms, Constitutive equations, Finite element analysis, Damage mechanics
Abdelhakim Aldoshan, Dehi P Mondal and Sanjeev Khanna
J. Eng. Mater. Technol   doi: 10.1115/1.4037657
The mechanical behavior of closed cell aluminum foam composites under different compressive loadings has been investigated. Closed cell aluminum foam composites made using the liquid metallurgy route were reinforced with multi-walled carbon nanotubes (CNTs) with different concentrations, namely; 1%, 2% and 3% by weight. The reinforced foams were experimentally tested under dynamic compression using the Split Hopkinson Pressure Bar (SHPB) system over a range of strain rates (up to 2200 s-1). For comparison, aluminum foams were also tested under quasi-static compression. It was observed that closed cell aluminum foam composites are strain rate sensitive. The mechanical properties of CNT reinforced Al-foams namely; yield stress, plateau stress and energy absorption capacity are significantly higher than that of monolithic Al-foam under both low and high strain rates.
TOPICS: Foams (Chemistry), Aluminum, Carbon nanotubes, Composite materials, Compression, Yield stress, Multi-walled carbon nanotubes, Weight (Mass), Pressure, Metallurgy, Absorption, Stress, Mechanical properties, Mechanical behavior
Kenan Cinar and Ibrahim Guven
J. Eng. Mater. Technol   doi: 10.1115/1.4037658
Micro-CT was used as a tool to investigate the deformation behavior of particulate-filled composite materials. Three different shapes of glass fillers (spherical, flake, and fiber) and fiber mass fractions (5%, 10%, and 15%) were introduced to the epoxy resin. Rockwell hardness H scale indentation test was used to deform the composite material. The composite materials were scanned before and after the indentation test by using micro-CT. Displacement field for each filler type and mass fraction were measured through correlation of before and after scan data. The effects of filler type and mass fraction on the internal displacement field were investigated. It was also demonstrated that micro-CT can be used as a tool to create realistic representative volume elements for particulate-filled composite materials instead of randomly distributed particles within the matrix material.
B. Ravi Kumar, Vishal Singh, Tarun Nanda, Manashi Adikary, Nimai Halder and T Venugopalan
J. Eng. Mater. Technol   doi: 10.1115/1.4037659
The authors simulated the industrially used continuous annealing conditions to process dual phase steels by using a custom designed annealing simulator. 67 % cold rolled steel sheets were subjected to different processing routes including the conventional continuous annealing line (CAL), inter-critical annealing (ICA), and thermal cycling (TC) to investigate effect of change in volume fraction, shape, and spatial distribution of martensite on tensile deformation characteristics of DP steels. Annealing parameters were derived using commercial software including Thermo-Calc, JMat-Pro, and DICTRA. Through selection of appropriate process parameters, the authors found out possibilities of significantly altering the volume fraction, morphology, and grain size distribution of martensite phase. These constituent variations showed a strong influence on tensile properties of DP steels. It was observed that thermal cycling route modified the martensite morphology from the typical lath type to in-grain globular/oblong type and significantly reduced the martensite grain size. This route improved the strength-ductility combination from 590 MPa-33% (obtained through CAL route) to 660 MPa-30%. Finally, the underlying mechanisms of crack initiation/void formation etc. in different DP microstructures were discussed.
R Seetharam, S Kanmani Subbu and M. J Davidson
J. Eng. Mater. Technol   doi: 10.1115/1.4037660
Grain size control of any engineering metals is very important in the hot upsetting process. Generally, the grain size directly controls the mechanical properties and performance of the material. The Al-B4C composite has extensive applications in nuclear industries, defense and electronic industries. Therefore, the aim of the present work is to study the dynamic recrystallization (DRX) behavior of Al-4%B4C composite during the hot upsetting test. The experimental works were performed on sintered Al-4%B4C preforms at various initial relative density (IRD) of 80%, 85% and 90%, and over the temperatures range of 300 oC - 500 oC and strain rates range of 0.1 s-1 - 0.3 s-1.The DRXed grain size of Al-4%B4C preforms various conditions of different IRDes, temperatures and strain rates were evaluated by using an optical microscope and it is significant for all tested conditions. The activation energy and Zener - Hollomon parameter of sintered Al-4%B4C preforms were calculated for various deformation conditions and IRDes. The mathematical models of DRX were developed as a function of Zener - Hollomon parameter for various IRDes to predict the DRXed grain size. It was found that DRXed grain size decreases with increasing Zener - Hollomon parameter. The verification has been done between measured and predicted DRXed grain size for various IRDes and, absolute error and mean absolute error were found to be 9.92% and 8.58%, respectively.
Dogan Acar, Mevlüt Türköz, Hasan Gedikli, Selçuk Halkaci and Omer N. Cora
J. Eng. Mater. Technol   doi: 10.1115/1.4037524
Warm hydromechanical deep drawing (WHDD) has increasingly been implemented by automotive industry due to its various benefits including mass reduction opportunities in auto body-in-white components, and improved formability for lightweight alloys. In the first part of current study, WHDD of AA 5754-O was studied. In order to obtain the highest formability, an optimization study was performed for AA 5754-O WHDD process parameters (tool temperature, hydraulic pressure and blank holder force loading profiles) through FEA + experimentation approach. Results showed that optimal temperature for punch is 25 °C; and 300 °C for die and blank holder. In addition, hydraulic pressure was found to be more effective on formability when compared to blank holder force. Both fast increasing hydraulic pressure and blank holder loading profiles contributes to higher formability.
TOPICS: Fluid mechanics, Optimization, Blanks, Pressure, Temperature, Alloys, Automotive industry, Finite element analysis
Pham Quang Trung, Khun Nay Win and David Butler
J. Eng. Mater. Technol   doi: 10.1115/1.4037525
Shot peening is well known as a surface deformation process which can induce compressive residual stresses into the subsurface of materials in order to improve the fatigue life. In this paper, the effects of the process conditions for both single and double shot peening on the fatigue life of AISI 4340 low alloy steel is investigated. The fatigue tests revealed that the shot peening process could significantly enhance the fatigue life of the treated components. However, a side effect of the process was an increase in surface roughness which was more prevalent under higher peening pressures and led to a reduction in the fatigue life. Therefore, to maximize the performance of the process, the peening parameters need to be carefully selected. Microstructure analysis of the shot peened parts indicated that the nucleation cracks or initiation cracks occurred in the subsurface at depths of 10 to 20 microns in the case of as-received samples but moved up to the free surface for the shot peened parts.
TOPICS: Shot peening, Alloy steel, Fatigue life, Fracture (Materials), Residual stresses, Fatigue testing, Surface roughness, Surface deformation, Nucleation (Physics)
Ahmad A Mousa, Gert Heinrich, Udo Wagenknecht and Omar Arrabeyat
J. Eng. Mater. Technol   doi: 10.1115/1.4037169
Exfoliated graphite (EXG) was prepared from commercially available natural graphite flakes (NGF), through strong acid treatment followed by thermal shock at 950 oC. The EXG sheets were characterized with respect to their thermal stability via thermo-gravimetric analysis (TGA) and Raman spectra. Their morphology and particle size were evaluated using scanning electron microscope (SEM) and particle size analyzer. The potential of EXG as reinforcement on the mechanical and thermal properties of the dynamically vulcanized polystyrene/styrene butadiene rubber (PS/SBR) composites were evaluated. The influence of EXG on the electrical properties of the composites was measured as well.
TOPICS: Composite materials, Thermal properties, Graphite, Particle size, Raman spectra, Thermal shock, Thermal stability, Electrical properties, Scanning electron microscopes, Styrene-butadiene rubber

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