A physically based constitutive model with internal state variables (ISVs) is established, it is used to describe the flow stress and microstructure evolution of Ti–6Al–4V alloy in the superplastic forming (SPF). The ISVs in the constitutive model includes the dislocation density, grain size, and the volume fraction of dynamic recrystallization. The flow stress consists of σ fd , σ ta , and σ GB , which are related to forest dislocation, thermal activation, and grain boundary sliding (GBS), respectively. The material constants of the constitutive model are determined, and the genetic algorithm (GA) optimization. A modeling method path to optimize the flow stress model is established, which is on the basis of the errors between the predicted and experimental flow stresses. In the modified flow stress constitutive model, the grain rotation (GR) is applied as a hardening mechanism, and the void is treated as a softening mechanism. A new GR model is proposed to describe the flow stress which is related to the GR. The modified constitutive model can accurately predict the evolution of yield stress, grain size and flow stress in SPF. With the calculation results of the multi-scales constitutive model, the mechanism of Ti–6Al–4V in SPF is discussed, and a new deformation map with dominant mechanisms for Ti–6Al–4V is obtained.

The microstructure, thermal behavior, and mechanical properties of Sn-xZn-0.1RE (x = 5, 10, 20, and 30 wt%) alloys containing mixed trace rare earth elements were investigated in this study. The results showed that the alloys had the same solidus temperature of about 199 °C. Zinc content higher than 10% enhanced slightly the eutectic temperatures and enlarged the eutectic temperature range of the alloys. The microstructures of most of the alloys exhibited Zn-rich coarse clusters, but not for Sn-5Zn-0.1RE. The tensile strength of the alloys increased with increasing zinc concentration.

The indentation formed on a metallic component by the high-velocity impingement of a small object can fracture the component, and this is known as foreign object damage. In this type of dynamic indentation, it is necessary to consider the effects of work hardening, strain rate hardening, and thermal softening in the impinged material. In this study, in order to consider these effects, the expanding cavity model based on a spherical formulation is modified via the Johnson–Cook constitutive equation for the dynamic indentation problem. Additionally, an equation is developed based on energy conservation and the modified expanding cavity model to predict the size of the indentation formed by an impingement of a solid sphere (EPIS). The distributions of equivalent plastic strain, equivalent plastic strain rate, temperature, and equivalent von Mises stress obtained via the expanding cavity model were in good agreement with the data obtained from the finite element analysis (FEA). Furthermore, it was demonstrated that EPIS accurately predicted the indentation size formed on various metallic materials at several impingement velocities in the range of 50–300 m/s. Consequently, EPIS can be effectively applied to an impingement problem of a hard sphere onto a sufficiently thick ductile material within 300 m/s without any help of FEA.

In the present study, RAMOR 500 armor steel plates were automatically welded using cold metal transfer arc welding (CMT), gas metal arc welding (GMAW) and hybrid plasma arc welding (HPAW) methods. To investigate the effects of the three different fusion welding methods on metallurgical and mechanical properties, the welded joints were examined using optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and also subjected to radiographic, hardness, tensile, and notched impact tests. The weld metal (WM) region of the GMAW and HPAW joints consisted of massive austenite. In the CMT welded joint the WM consisted mainly of dendritic austenite and a minor amount of d-ferrite. Regardless of the welding process, the hardness of both the WM and HAZ (Heat Affected Zone) regions were found to be higher than the base metal (BM). The tensile strengths obtained by CMT, GMAW, and HPAW were 45%, 50% and 65% of the BM, respectively. Cleavage-type brittle fractures occurred in the HPAW and GMAW welded joints, while localized ductile fractures occurred in the CMT joints. The joints welded by HPAW and GMAW fractured from the HAZ, and the joint welded by CMT fractured from the WM in the tensile tests. In terms of notch toughness, the CMT joints exhibited better impact resistance compared to the BM. HPAW and GMAW joints displayed less impact resistance than the BM, with values comparable to previous studies in the literature.

In this study, parent aluminium (Al), silicon carbide (SiC) reinforced Al, zirconia (ZrO 2 ) coated SiC reinforced Al and lithium zirconate spinel (Li 2 ZrO 3 , LZO) encapsulated SiC incorporated Al metal matrix composites were processed via friction stir processing (FSP) technique to observe the influence of grain refinement on mechanical and damping properties. Electron back scattered diffraction (EBSD) analysis were conducted for detailed and deep understanding of possible mechanism and microstructure at longitudinal cross-sections of the samples. Further, the room temperature mechanical properties and thermal cyclic (−100 to 400 °C) damping performance of the friction stir processed composites were studied. The results obtained in this investigation show that storage modulus of pristine Al, SiC reinforced Al, ZrO 2 coated SiC reinforced Al and LZO coated SiC reinforced Al were improved by a factor of 1.09, 1.17, 1.09 and 1.38, respectively after FSP. Additionally, the ultimate tensile strength (UTS) and hardness of the friction stir processed SiC/Li 2 ZrO 3 /Al composite were improved by a factor of 1.08 and 1.11, respectively after FSP compared to un-processed composite.

Under the compression mode, the direction of force on the magnetorheological elastomer (MRE) is parallel to the direction of electromagnetic force, so the effect of electromagnetic force on its dynamic mechanical properties cannot be ignored. Therefore, this paper focuses on the effect of electromagnetic force on the dynamic mechanical properties of MRE under compression mode. A new type of testing device was designed and processed. Under a different loading frequency, strain amplitude and external magnetic field, dynamic mechanical properties of MRE were tested, respectively. The result shows that the stiffness and energy dissipation capacity of MRE increase with the current and loading frequency. The stiffness of MRE decreases with the increase in the strain amplitude, but the energy dissipation capacity increases. Comparing the force-displacement curve of MRE with or without the effect of the electromagnetic force, it shows that the electromagnetic force has a great effect on the stiffness of MRE and little effect on its energy dissipation capacity. When the electromagnetic force is removed, the stiffness of MRE decreases, and the change rate of stiffness increases with current. The maximum change rate of stiffness is 5.65%.

This study attempts to provide a theoretical estimate coupled with an analysis of the measured data to predict pitting damage of an aluminum alloy 2219 under the conjoint influence of mechanical load and corrosive environment. In accordance with the basic principle of crater growth coupled with the synergistic influences of mechanical and chemical effects, the law governing the presence and growth of corrosion pits was studied. Based on the concept of microscopic damage mechanics, porosity as a damage variable was introduced and the resulting model for estimating the reduction in elastic modulus of the material that has experienced observable damage due to pitting was established. Accelerated corrosion tests and uniaxial tensile tests are carried out, and a research-grade microscope coupled with a laser range finder was used to study the formation, presence and growth of the pits with time. It was found that the corrosion pit in the chosen aluminum alloy can be simulated as a semi-ellipsoid, and the relationship between depth of the pit and applied stress is an exponential function. This enabled in establishing the influence of alloy chemistry on nature, extent and severity of damage due to pitting. The macroscopic morphology of the damaged specimens after corrosion was carefully observed and analyzed. The influence of time of exposure to the environment and applied load on damage due to pitting was verified. A comparison between the calculated results and experimental data reveals an overall correctness of the method developed and discussed in this paper.

The types of biomedical devices that can be three-dimensional printed (3DP) are limited by the mechanical properties of the resulting materials. As a result, much research has been focused on adding carbon nanotubes (CNT) to these photocurable polymers to make them stronger. The objective of this study was to expand the use of 3DP to prosthetics by testing the hypothesis that adding CNTs to a stereolithographic (SLA) photocurable resin will result in a cured polymer with increased impact and fatigue resistance. For impact testing, twenty-six total specimens, 13 with nanotubes and 13 without nanotubes, were printed on a Form2 SLA printer. Once all the specimens were printed, washed, and cured, the impact resistance was quantified using a pendulum impact tester using a notched Izod configuration. Similarly, twelve R. R. Moore fatigue specimens were printed, washed, and cured. The specimens with SWCNTs (0.312 ± 0.036 ft lb/in.) had a significantly lower impact resistance compared to the non-SWCNT specimens (0.364 ± 0.055 ft lb/in.), U = 34.0, p = 0.004. Adding SWCNTs also reduced the short cycle fatigue life (i.e., 10 3 ) from 3.1 × 5 to 8.8 × 3 psi and increased the endurance limit from 0.4 to 3.0 × 3 psi. If used for creating a foot prosthetic, the non-SWCNT polymer would last 2919 cycles while the SWCNT mixture would last <1 cycle. Therefore, SLA polymers do not yet have the impact and fatigue resistance capabilities to be used for prosthetic feet.

Three-dimensional (3D) reconstruction and finite element method are combined to study the damage behavior of aluminum alloy resistance spot-welded joints. Fatigue damage of spot-welded joints under different cyclic loading stages was obtained by X-ray microcomputed tomography (X-ray micro CT). Then, avizo software was used to reconstruct the scanned data of joints with different damage degrees, and the distribution and variation of defects in the joints are obtained. On this basis, 3D finite element damage models were established. Finite element calculations were carried out to analyze the fatigue damage of spot-welded joints by adopting the effective elastic modulus as the damage parameter. The results show that the effective elastic modulus is consistent with the experimental results. The method of combining 3D reconstruction with the finite element method can be used to evaluate the internal damage of spot-welded joints and provide theoretical basis for the prediction of fatigue life.

A combined experimental and micromechanics investigation is conducted on elevated-temperature thermal expansion of PTFE/PEEK polymer-matrix composite reinforced with randomly oriented short carbon fibers (CF) and graphite flakes (Gr). In the experimental phase of the study, PTFE/PEEK polymer blends with different amounts of PTFE and four-phase CF/Gr/PTFE/PEEK composites with different volume fractions of graphite flakes were made from compression molding. Scanning electron microscopy was performed to evaluate the microstructure of the PTFE/PEEK matrix and the composite, especially the interface, and the size and dispersion of the particles. X-ray diffraction (XRD) was conducted to provide morphological information on the semi-crystalline PTFE/PEEK matrix of the composite. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were carried out to determine transition temperatures and thermomechanical properties of the composite and its constituent phases at the elevated temperature. Thermal expansions of neat PTFE and neat PEEK, the PTFE/PEEK polymer matrix, and the CF/Gr/PTFE/PEEK composite were obtained with a thermal–mechanical analyzer (TMA) in a dilatometric mode. Coefficients of thermal expansion (CTEs) of the PTFE/PEEK matrix and its CF/Gr/PTFE/PEEK composite were then determined from 25 °C up to an elevated temperature 240 °C. To augment the experimental study, micromechanics analyses are also conducted to determine thermal expansion coefficients of the PTFE/PEEK matrix and the CF/GR/PTFE/PEEK composite. The micromechanics solutions elucidate individual roles of different composite constituents, contributions of individual constituent materials’ temperature-dependent thermal and mechanical properties, the importance of composite microstructure and morphology, and the issue of thermal–mechanical coupling on the thermal expansion behavior of the complex CF/Gr/PTFE/PEEK composite at high temperature.

This paper presents predictions of the mechanical response of sintered FGH96 Ni-based superalloy powder compacts at high temperatures, obtained by the analysis of 3D representative volume elements generated by both X-ray tomography and a virtual technique. The response of the material to a multi-axial state of stress/strain for porosities as large as 0.3 is explored, obtaining the yield surfaces and their evolution as well as scaling laws for both elastic and plastic properties. The two modeling approaches are found in good agreement. The sensitivity of the predictions to particle size, inter-particle friction, applied strain rate, and boundary conditions is also examined.

The present study intends to evaluate local ratcheting and stress relaxation of medium carbon steel samples under various asymmetric load levels by means of two kinematic hardening rules of Chaboche (CH) and Ahmadzadeh-Varvani (A-V). The Neuber's rule was coupled with the hardening rules to predict ratcheting and stress relaxation at the vicinity of notch root. Stress-strain hysteresis loops generated by the CH and A-V models were employed to simultaneously control ratcheting progress over stress cycles and stress relaxation at notch root while strain range kept constant in each cycle. The higher cyclic load levels applied at notch root accelerated shakedown over smaller number of cycles and resulted in lower relaxation rate. The larger notch diameter of 9mm on the other hand induced lower stress concentration and smaller plastic zone at notch root promoting ratcheting progress with less materials constraint over loading cycles as compared with notch diameter d=3mm. Predicted ratcheting results through the A-V and CH models as coupled with the Neuber's rule were found in good agreements with experimental data. The choice of A-V and CH hardening rules in assessing ratcheting of materials was attributed to the number of terms/coefficients and complexity of their frameworks and computational time/CPU required to run ratcheting program.

Standard-compliant measurement of the in-plane fracture toughness of metals (i.e., in the SL or ST directions per ASTM standard denominations) is often impossible due to insufficient material in the through-thickness direction to extract a full Single Edge Bending (SEB) or Compact Tension (CT) fracture specimen. In the present work, we propose a new specimen design methodology to overcome this challenge. A W-shaped SEB specimen (called W-SEB) was developed in this study and its topology optimized using finite element simulations. The new specimen design was validated numerically and experimentally on a case study and results showed excellent agreement with stand-ard ASTM E1820 full SEB specimen measurements. In view assessing the anisotropy of the fracture toughness (K Q and CTOD) of pipeline steels susceptible to hydrogen in-duced cracking (HIC), the W-SEB specimen was used on X65 and X42 pipeline steel samples taken from the field. Experimental results show an increase in the maximum CTOD in the SL direction as compared to the LT direction for both steel grades. Such experimental results could lead to important considerations with respect to accurate fit-ness for service assessment of HIC damaged assets.

Homogenization heat treatment is performed to attain uniformity in microstructure which is helpful to achieve the desired workability and microstructure in final products and, eventually, to gain predictive and consistent performance. Fabrication of low-enriched uranium alloys with 10 wt% molybdenum (U-10Mo) fuel plates involves multiple thermomechanical processing steps. It is well known that the molybdenum homogeneity in the final formed product affects the performance in the nuclear reactor. To ensure uniform homogenization, a statistical method is proposed to quantify and characterize the molybdenum concentration variation in U-10Mo fuel plates by analyzing the molybdenum concentration measurement data from scanning electron microscopy energy dispersive spectroscopy line-scan. Statistical tolerance intervals (TI) are employed to determine the qualification of the U-10Mo fuel plate. We formulate an argument for the minimum number of independent samples to define fuel plate qualification if no molybdenum measurement data are available in advance and demonstrate that the given TI requirements can be equivalently reduced to a sample variance criterion in this application. The outcome of the statistical analysis can be used to optimize casting design and eventually increase productivity and reduce fabrication costs. The statistical strategy developed in this paper can be implemented for other applications especially in the field of material manufacturing to assess qualification requirements and monitor and improve the process design.