Papers by Keyword: Pre-Stretching

Abstract: The effect of pre-stretching and under-aging treatment on microstructure and fatigue crack resistance of Al-4.1Cu-1.27Mg-0.47Mn-0.02Ti alloy has been investigated in present work. The results showed that the fatigue strength corresponding to 10⁷ stress cycle numbers of the sample pre-stretched 4% and under-aged at for 2 hours reached up to 280MPa, 80MPa higher than that pre-stretched 0% and peak-aged at for 8 hours. Microstructural observations showed that fine and uniformly dispersed S’ plates were present in the sample treated by pre-stretching and under-aging, whereas, a coarse S’ plate was formed in the sample when treated by 0% pre-stretching and peak-aging. It is indicated that the pre-stretching and under-aging treatment promotes the dispersoid formation of strengthening particles, enhancing the fatigue crack resistance and resultant fatigue strength. Keywords: Al-Cu-Mg alloy, fatigue, pre-stretching, aluminum alloy casing pipe

Abstract: The effect of the inhomogeneity of the material properties on the quenching residual stress in the aluminum alloy was studied by using the finite element method simulation and the evolution of the quenching residual stress during the pre-stretching process was discussed in this paper. The results show that both the x-component and y-component of the quenching residual stresses in the non-uniform model are nearly overlapped with that in the uniform model. The effect of the inhomogeneity of the material properties on the quenching residual stress is negligible. After pre-stretching, the surface stress of the non-uniform model decreases from the middle line to the edge while the center stress increases. Contrastingly, both the surface and center stress of the uniform model are nearly stable along the same path, and the stress magnitudes are lower than that in the non-uniform model. The inhomogeneity of material properties mainly affects the pre-stretching residual stress distribution, while it has little effect on the quenching residual stress distribution.

Abstract: The article established a modelling that predicted and measured the quenching and pre-stretching stress in 7050 aluminum alloy thick plate in order to make the alloy suitable enough for manufacturing in the aerospace industries. The results show that both the rolling direction component stress and the transverse direction component stress have a “M” distribution along the plate thickness of 7050 aluminum alloy thick plate, but the level is slightly different, but the level is slightly different. The maximum value of quenching residual stress is about 187MPa in the 80mm thick of 7050 plate. Pre-stretching of the heat treated and quenched alloy to 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0% and 3.5% to reduce the residual stresses. It has been recorded that more than 90% reduction of residual stresses were observed in a pre-stretching rage of 2-3%. Measuring the surface residual stresses of the alloy by ultrasonic methods and measuring the internal residual stresses of the alloy by crack compliance methods. The two methods are used to verify the model. The difference between the measurement and the simulation is within 40MPa. The experimental data of the ultrasonic and the crack compliance methods were found to correspond well with the simulated models. This shows that the simulation model can effectively predict the evolution of residual stress in 7050 aluminum alloy thick plate, and the simulation model can also be reconstructed and inspected through the experimentally measurement.

Abstract: Through a series of mechanical properties tests and microstructure observation, the effects of artificial heat treatment (AA), pre-stretching aging (PA) and pre-stretching creep aging (PCA) treatment on the precipitation phase type and mechanical properties of X2A66 aluminum-lithium alloy were studied. The results show that compared with AA, PA treatment promotes the uniform precipitation of high-density T₁ phase, so that the yield strength, tensile strength and elongation of the alloy reach 593.4Mpa, 610.8Mpa, 10.7%. Further, the creep aging treatment on the basis of the pre-deformation can further increase the strength (613.6Mpa, 628.9Mpa) of the alloy with a slight decrease in the elongation (10.3%).

Abstract: In this work, Forming Limit Curves (FLCs) of the conventional and pre-stretched High Strength Steel (HSS) sheet grade 440 (SCGA440-45) were investigated. The conventional forming limit curve was experimentally determined by using the Nakajima stretching test. Subsequently, the non-linear strain path FLCs were precisely developed through the Nakajima stretching test after the specimens were pre-stretched in biaxial direction up to several levels on the Marciniak In-plane stretching test. The gained non-linear strain path FLCs were compared with the conventional FLC.Additionally, the experimental Forming Limit Stress Curve (FLSCs) were calculated using the experimental FLC and non-linear strain path FLCs data from investigated steel sheet. The yield criterion Hill’48 was employed in combination with the Swift strain hardening law to describe anisotropic deformation and plastic flow behavior of the HSS sheet, respectively. Hereby, the influence of pre-stretching levels on the experimentally determined the FLCs and FLSCs were examined. The results prove a significant influence of the pre-stretching levels on the both FLCs and FLSCs of the investigated HSS sheet. For a low pre-stretching in biaxial loading the FLCs demonstrated a reduced formability and the FLSCs exhibited the limited stress levels depending on the experimental FLC data.

Abstract: A discretization method is used in pre-stretching simulation to separate an aluminum alloy thick plate into layers. When the equivalent plastic strain in each layer is defined according to the residual stresses during quenching, the yield strength model can be developed to estimate its yield strength. Again, the curve of elasticity modulus is fitted in the light of the experimental data, which can reveal how the elasticity modulus changes with plastic deformation. Finally, in consideration of the non-uniformity of yield strength and elasticity modulus, the pre-stretching of the quenched 7075 aluminum alloy thick plate is taken as an example to numerically simulate the value and distribution of residual stresses at the pre-stretching ratio of 1.8%, 2.2% and 2.5%, respectively. It is known from the simulated results that, by using the proposed method in this paper, the obtained results of the distribution and magnitude of the residual stresses are in good agreement with the experimental measurements.

Abstract: The finite element method (FEM) was used to study the quenching and pre-stretching residual stresses of the 7085 aluminum alloy plate, combining with experimental measurement. Quenching residual stress simulation results showed that the stress of the rolling-direction and transverse-direction in the center were 16.5MPa and 9.2MPa, respectively. The stress of the rolling-direction and transverse-direction on the surface were-33.8MPa and-40.4MPa, respectively. The quenching residual stress simulation results were in good agreement with the X-ray diffraction experimental results. As the pre-stretching ratio increases, the quenching residual stress reduction ratio increases. The ratio of 2.0~3.0% pre-stretching can effectively release the quenching residual stress in aluminum alloy plates. After 3.0% pre-stretching, the stress of the rolling-direction and transverse-direction in the center were 0.9MPa and 1.8MPa, respectively. The stress of the rolling-direction and transverse-direction on the surface were-3.6MPa and-7.1MPa, respectively. The quenching residual stress reduction ratio reached above 80%.

Abstract: In this paper, the effect of pre-stress of ball screws on bending stiffness is studied. By using ANSYS APDL parameterized method and adding stress stiffness effect, the relationship between the maximum deflection of ball screws under gravity load and pre-stress is given. The research result shows that with the increasing of pre-stress, the maximum deflection of the ball screw under gravity load gets smaller nonlinearly. The effects of pre-stretching of the ball screw on bending stiffness vary with different cross sections.

Abstract: Abnormal pre-stretching of aluminum alloy thick-plate is simulated by using Marc FEM software to obtain the stress distribution of the plate under non-uniform clamping condition and material macroscopic deficiency. By analyzing the distribution contours, stress distributing characteristics of the pre-stretched thick-plate and their effects to rolling yield of thick plates under several typical cases are classified and summarized. Moreover, solving measures and advices are presented to reduce the negative effects.

Abstract: By researching on the main factors affecting the active zone area strain of electroactive dielectric elastomers, the suitable conditions of area strain for the material in the application as artificial muscles actuator was determined. In the experiments, the strain characteristics of the material was investigated under uniaxial pre-stretching, uniform biaxial pre-stretching and non-uniform biaxial pre-stretching respectively. In addition, the strain rates of the materials active zone under different ratio of the active zone to the window radius of the materials were investigated. The experimental results show that the area strain of active zone would have inflexion under any pre-stretching condition, and the area strain increased with applied voltage increasing, decreased with the ratio of the active zone to the window radius increasing. It could be found that the strain conditions have an important influence on the area strain of the active zone.