Strength of Materials最新文献

Due to critical vibration and excess weight in the frame structure of the automobile, the automobile acceleration effects are the primary problems. This paper describes the material selection based on its weight, vibration reduction, and increasing vehicle performance. The front cabins heavy-duty van frame was considered for this research work and designed according to the frame dimension. Generally, the frame is made of mild steel and replaced by high-strength extrusion magnesium alloy. The frame structures crash and impact analysis was investigated using nonlinear buckling and transient analysis. The stress, vibration and nonlinear buckling analysis was obtained under different loading conditions. The bending performance of the frame was analytically investigated and verified with the FEA code (ANSYS 15.0).

This paper systematically analyzed and discussed the microstructure and mechanical properties of as-cast AZ61 magnesium alloy with rare-earth content of 1.0~4.0 wt.% by optical microscopy, SEM, EDS, and XRD. The results indicate that in addition to the obvious distribution of skeletal β-Mg₁₇Al₁₂ phase, a small amount of Mg₃₂(Al, Zn)₄₉ quasicrystal phase is distributed in as-cast AZ61 alloy. With the addition of rare-earth content, the skeletal β-Mg₁₇Al₁₂ phase dendrites in the as-cast AZ61 magnesium alloy matrix are decomposed obviously. The dendrite decomposition is more serious with increased Rare-earth content, and the quasicrystal Mg₃₂(Al, Zn)₄₉ disappears. When the rare-earth content is 1%Ce~2%Ce, the alloy mainly consists of needle-like, dot-like, or clustered Al₄Ce and Al₈Mn₄Ce phases with a small amount of Al₄La. When 2.8%Ce+1.2%Nd mixed rare-earth was added, the Al₈Mn₄Ce phase was not found in the alloy but mainly composed of Al₃Nd and Al₄Ce rare-earth phases. These rare-earth phases were radiative needle-like, willow leaf-like, rod-like, spot-like, layer-like, and a little irregular block. The as-cast AEZ641(2.8 wt.% Ce+1.2 wt.% Nd) magnesium alloy has the best comprehensive performance, and the yield strength is 2% higher than the as-cast AZ61 alloy. Its tensile strength, hardness, and elongation are similar to as-cast AZ61 alloy. The fracture mechanism of as-cast AZ61 + xRE is mainly a cleavage-type brittle fracture.

The paper considers the use of hydrogen as a component of the technological process to solve an applied problem - the control of material defects, which consisted of controlled fragmentation of steel under dynamic loading to facilitate the cracking of the metal volume. Medium-carbon pearlite-ferrite steel of steel 60 types under electrochemical hydrogenation is studied. The criterion parameter of the material state was the energy of impact loading by three-point bending of smooth beam specimens. By selecting the electrochemical hydrogenation modes in terms of intensity (current) and duration of the process, as well as the composition of the electrolyte, a significant reduction in the energy intensity of steel fracture was obtained, which correlates with the residual hydrogen concentration in the metal. Metallographic analysis of the surface of the specimens confirmed the hydrogenation effect on the initiation of defects, which can be used for controlled steel fragmentation.

The paper presents the results of an experimental study of the deformation properties of 10GN2MFA and 15Kh2MFA steels at different ratios of principal stresses under cyclic loading conditions. Applying the proposed phenomenological approach of an improved elastic-viscoplastic model allows one to qualitatively describe the effects of the influence of structure degradation under the action of temperature and force factors that accompany the operation of actual structural elements significantly affecting the regularities of deformation and damageability and the strength of structural materials under combined stress conditions. An evaluation of the variation rate in the homogeneity of the studied steels at different ratios of principal cyclic stresses under cyclic creep conditions is presented. Based on the experimental results, correlation dependences between the relative values of the homogeneity coefficient and the function of the deformation properties of the material and the type of stress state were obtained, which significantly simplifies the determination of the parameters characterizing the limiting state of the structural element.

Member stiffness in bolted connections has been widely studied for homogenous and isotropic materials contrary to composite sandwich ones. Therefore, a numerical simulation based on the augmented Lagrangian algorithm to solve contacts problems is conducted in ANSYS software to investigate various preloaded sandwich bolted joints with carbon and glass laminate skins and two types of foam cores. Tested samples show a rise of the ratio of maximum shear stress to maximum principal stress when the applied preload increases considerably which improves the risk of core failure, additionally, an analytical approximation of stiffness at preload is proposed, for that, a search algorithm is used to deduce the expression of the equivalent elastic modulus of tested joint members and a distance correlation method is applied to determine the theoretical formulation of the introduced stiffness model whose accuracy is optimized through analyzing results of root mean square error (RMSE) of its mathematical approximations , the convergence of the chosen model is ensured for all tested samples except the ones having the most rigid skins with the greatest elastic modulus (209 GPa). Furthermore, the equation introduced by Zhang and Poirier concerning the tension load causing a bolted joint separation is adapted and validated with a percent error less than 13%.

With the development of various multi-composite materials, there are several methods to study the mechanical properties of materials with complex microstructures. As a typical multi-composite material, foam concrete’s mechanical properties and research methods are also widely concerned. To predict the mechanical properties of foam concrete more quickly, we use Python software to realize the random generation of foam pores to establish a random three-dimensional geometric model of foam for many foam concrete materials. Based on the random foam three-dimensional geometric model, the equivalent parameters of foam concrete are calculated by the method of calculating the equivalent parameters of materials in mesomechanics. The relationship of equivalent material parameters between porosity and foam pore diameter is sought. Finally, the tensile calculation of a foam concrete cube with a cohesive unit is carried out to study its stress-strain distribution and the initiation and development of cracks.

A mechanophysical model for crack growth kinetics computation on stress corrosion fracture of modified 06G2BA and 08KhMCHA pipe steels is adequately expressed through the plane stress-strain state dα/dt and dJ/dt ratios that are dependent on the strain crack tip rate. The crack growth accelerated by an aggressive environment occurs under static and cyclic loading due to transient dissolution and repassivation processes at the crack tip. Such accelerations are divided into three categories, determined by the strain rate: mechanical cracking (fatigue crack and stationary plastic crack), corrosion-accelerated mechanical cracking (corrosion fatigue and corrosion-accelerated plastic crack), and sulfide stress corrosion fracture. Metallographic studies revealed the change in the crack nucleation and propagation mechanisms, from transcrystalline to intercrystalline, related to the viscoplastic and brittle structure of steel specimens cyclically loaded and simultaneously affected by a corrosive environment.