Mean Equivalent Strain Research Articles

Compaction behavior and densification mechanisms of Cu[sbnd]W composite powders

The deformation mechanism related to the initial relative density and uniformity of CuW composite powders under quasi-static compression was investigated by multi-particle finite element method. The results show that under the same pressure, the relative density of powder increases with the increase of initial relative density or the uniformity of composite powders. The densification processes can be divided into three stages, namely particle rearrangement, Cu particle deformation and W particle deformation. Pores are mainly filled by the rearrangement of particles and the deformation of Cu particles. The rearrangement and deformation of particles are quantitatively characterized by introducing the mean rotation degree and the mean equivalent strain of powders. It is found that smaller voids formed in the initial denser powder are easily filled by the deformation of adjacent particles during compaction. Strong force chains formed by the contact of W particles severely hinder the compression, resulting in large porosity.

Optimization of Process Parameters for Closed-die Forging Based on Finite Element Simulation

In this study, finite element software was used to simulate and optimize the process parameters including billet thickness, forging speed, and friction coefficient during closed-die forging. The results show that the mean equivalent strain of the billet gradually increases as the thickness reduces. However, the corners of the billet show certain arcs and the materials are insufficiently filled when the thickness is too small. The higher the die-forging speed is, the more significantly the temperature rises and the more non-uniformly the temperature distributes in the billet. In addition, the mean equivalent strain shows little change when the friction coefficient increased from 0.1 to 0.3, but the strain distribution became more inhomogeneous.

Investigation of Bonding Behavior of AA1050/AA5083 Bimetallic Laminates by Roll Bonding Technique

In this study, 1-mm AA1050/AA5083 bimetallic laminates were produced using roll bonding (RB) process. The RB process was carried out with thickness reduction ratios of 25, 50 and 75%, separately. Finite element simulation was used to model the deformation of bimetallic laminates for various experimental conditions. Particular attention was focused on the bonding of the interface between AA1050 and AA5083 layers in the simulation. The optimization of thickness reduction ratios was obtained for improvement of the bond strength of bimetallic laminates during RB process. During the simulation, the mean equivalent strain at the interface zone between the layers was found to reach the maximum value with a high quality bond for the sample produced with 75% of thickness reduction. Moreover, the fracture surface of samples around the interface of laminates after the tensile test was studied to investigate the bonding quality by scanning electron microscopy.

On the introduction of a mean stress in kinetic damage evolution laws for fatigue

An evolutive mean value z̆ is defined for complex loadings. It is shown to be independent from the loading shape and it tends toward the classical mean value zmean=z‾=12zmin+zMax for a periodic loading. The proposed definition applies to quantities encountered in the fatigue modeling of different materials: mean stress or mean hydrostatic stress for metals, mean damage driving force or mean equivalent strain for quasi-brittle materials or for composites. It gives the possibility to introduce the adequate mean stress effect in kinetic (rate) damage evolution laws. This point is illustrated for woven interlock composites in two steps, (i) by proposing an original modeling of the asymptotic Haigh diagram and (ii) by the description of full mean stress effect from kinetic damage evolution laws. The concept of evolutive mean stress gives the possibility to model fatigue under complex loading with no need to define a cycle. It applies to random fatigue as shown in different examples.

An upper bound solution for twist extrusion process

Twist extrusion, a promising severe plastic deformation technique for grain refinement down to ultrafine/nanocrystalline microstructures, was introduced as an attempt to provide large plastic deformation conditions similar to those in high pressure torsion while allowing large workpiece dimensions for industrial applications. As a relatively new severe plastic deformation technique, twist extrusion requires in-depth investigation of its plastic deformation characteristics. In this study, the twist extrusion process with a square shape die cavity has been analyzed using an upper bound solution to estimate the required power, deformation pattern, and optimum process condition. The analysis has been performed based on two kinematically admissible velocity fields while the effects of friction condition, die geometry, and mean equivalent strain have been considered. The results indicate that the die geometry and process parameters can dramatically change the deformation pattern and extrusion power.

An Investigation of Interface Bonding of Bimetallic Foils by Combined Accumulative Roll Bonding and Asymmetric Rolling Techniques

The bond strength in bimetallic materials is an important material characteristic. In this study, 0.1-mm thick bimetallic foils (AA1050/AA6061) were produced using one pass of accumulative roll bonding followed by three passes of asymmetric rolling (AR). The AR passes were carried out at roll speed ratios of 1.0, 1.1, 1.2, 1.3, and 1.4 separately. Finite element simulation was used to model the deformation of the bimetallic foils for the various experimental conditions. Particular attention was focused on the bonding of the interface between AA1050 and AA6061 layers in the simulation. The optimization of the roll speed ratio was obtained for improvement of the bond strength of the interface of AA1050/AA6061 bimetallic foils during AR process. In the simulation, the mean equivalent strain at the interface zone between the AA1050 and AA6061 layers was seen to reach a peak value at a roll speed ratio of about 1.2 to 1.3, which also corresponded to a high quality bond at the interface as observed experimentally.

Microstructure and texture evolution of Al during hot and cold rolling

The evolution of microstructure and texture of commercial purity Al during hot and cold rolling has been studied. The results show that the dynamic restoration mechanism for Al rolled to a total equivalent strain of 2.66 at a mean equivalent strain rate of 14.4 s-1 at 510 °C is essentially dynamic recrystallization (DRX), whereas for those materials deformed to lower strains at lower strain rates at this temperature, the restoration mechanism is mainly dynamic recovery (DRV). This is confirmed by examining the microstructures, textures, and substructures of the material developed during hot rolling as well as by comparing the results with those developed during cold rolling and annealing. The texture analysis using orientation distribution functions (ODFs) indicates that the dynamically recrystallized material has a random orientation distribution, whereas dynamically recovered materials have a developed deformation texture with a predominantD component and a Cu component. The substructure observation by transmission electron microscopy (TEM) indicates that the subgrains in the dynamically recrystallized material are completely dynamically recovered, which is very similar to those subgrains in cold-rolled material. However, the annealed material shows a completely different substructure. By studying all of these structural features, which are closely associated with the dynamic restoration mechanism, it is confirmed that Al undergoes DRX in the present work, which is different from either DRV or static recrystallization (SRX).

Estimation of plastic constraint and local strain at the notch root for notched plates and bars.

Plastic constraint and local strain at the notch root for notched plates and bars were examined in the elastic-plastic and full plastic regions by FEM. By introducing the mean equivalent stress, σ(Mises), and the strain, e, at the minimum cross section, and the equivalent stress concentration factors, Kt, the results obtained in this study are summarized as follows: (1) The plastic constraint factor k defined by σ/σn was nearly constant under the wide range of deformations, and independent of the material constants. (2) The general yield stress σGY was derived based on the idea that the mean equivalent strain in the elastic state is almost equal to that in the plastic state. (3) The relationship between σ and e for σ≥σGY was approximately in accord with the constitutive equation of the materials and was e=Bσm for σ≤σGY. (4) The equivalent strain, e, at the notch root was simply estimated from e=Kt e.

Temperature and speed effects in hot extrusion of aluminium alloys

Extrusion is shown to be a thermally activated process in which mass transfer is important. Speed effects may be recognized in the mean equivalent strain rate and then combined with temperature eff...