Surface Hardening of High-Strength Low Alloy Steels (HSLA) Dual-Phase Steels by Ball Burnishing Using Factorial Design

Burnishing is used increasingly as a finishing operation which gives additional advantages such as increased hardness, fatigue strength, and wear resistance. Experimental work based on 3⁴ factorial design was carried out to establish the effects of ball burnishing parameters on the surface hardness of high-strength low alloy steels (HSLA) dual-phase (DP) steel specimens. Statistical analysis of the results shows that the speed, feed, lubricant and ball diameter have significant effect on surface hardness.     

新型建筑材料在基础工程中的应用

重点介绍了在地基基础和基坑围护方面7种新型建材的特性和应用现状,并预测了新型建材在基础工程中的发展趋势。     

Effect of C/Ti ratio on the laser ignited self-propagating high-temperature synthesis reaction of Al-Ti-C system for fabricating TiC/Al composites

TiC/Al composite was successfully synthesized utilizing laser ignited self-propagating high-temperature synthesis (SHS) of Al-C-Ti system with the different C/Ti molar ratio. When the molar ratio of C to Ti is below 1:1 in the starting materials, in addition to fine TiC particulates, a large amount of Al₃Ti phase was found in the composites; however, when the molar ratio of C to Ti is 1:1 in the starting materials, the Al₃Ti phase was almost completely eliminated and the distribution of TiC particulates generally appeared to be more homogeneous throughout the products synthesized.     

Allowables-Based Flow Curves for Nonlinear Finite-Element Analysis

A methodology for developing allowables-based stress versus strain relationships for metal alloys is presented. The approach incorporates Federal Aviation Administration/Department of Defense (FAA/DoD) Metallic Materials Property Development and Standardization (MMPDS) statistically derived material properties for tensile yield and ultimate strengths to derive flow curves at room or elevated temperature with an A-, B-, or S-Basis probability. The resulting flow curves may be used for new designs to comply with Federal Air Regulations as well as for forensic investigations and failure analysis.     

Development of Boundary Structures for Complex-Shaped Buildings

Over the past few years, the field of architecture has witnessed revolutionary changes in design. The recent completions of Frank O. Gehry’s projects brought unprecedented attention to complex-shaped, nonconventional design. In following these latest trends, the author has been drawn to the issue concerning the structural systems currently being adopted in realizing these complicated designs. It is perhaps inevitable that the traditional structural systems, comprised of structural elements suitable for use in conventional linear shapes, face tremendous challenges and limitations in building such complicated designs. In this context, this research consists of proposing a new alternative by employing “boundary structures with continuously changing curvature,” which follow the complex-curved envelope surface, as well as fabricating an experimental model made of polymer composite materials with computer-aided design/computer-aided engineering/computer-aided manufacturing technologies. Consequently, the study aims at offering architects unprecedented freedom in design and a new paradigm for realizing their creative ideas.     

Delamination Analysis for Laminated Composites. II: Numerical Verification

A validation of the delamination analysis models developed in a companion paper is provided through comparisons of predictions with finite‐element and elasticity solutions. The models are applied to the analysis of composite compression specimens reinforced with end tabs. An elasticity solution for the gage section of the specimens is developed. A comparison of the characteristic roots shows that the predictions of the models include the material and geometric parameters that control the behavior, and the roots corresponding to the basic stretching and bending modes are accurately predicted. The stress distribution at the interface between tabs and specimen is in good agreement with a finite‐element simulation. The interlaminar shear and peel stresses show an exponential increase with a maximum intensity at the free edges of the tabs. The behavior of previously tested specimens is explained; and practical guidelines for specimen design are provided to avoid unwanted extraneous modes of failure. The influence of the deformation modes associated with each model is investigated. An assessment of the accuracy and level of complexity is presented.     

镁基储氢材料的研究进展

本文回顾和总结了近几十年来，特别是近十年来镁基储氢材料的发展情况，重点综述了机械合金化Mg-Ni2合金体系的研究情况及其近期的进展，从储氢材料成份及配比，制造工艺改进以及材料的组织结构对材料性能的影响等各方面进行一定的分析和归纳，对储氢材料研究中出现的问题以及今后的发展方向都作了探讨。     

Pressureless sintering and characterization of cordierite/ZrO2 composites

Cordierite/ZrO₂ composites with 5 to 25 wt% ZrO₂ were fabricated by conventional powder mixing and pressureless sintering method. Their densification behavior, microstructure, mechanical and thermal properties were studied. By dispersing 25 wt% (9.57 vol%) ZrO₂, densified cordierite/ZrO₂ composite with a relative density of 98.5% was obtained at an optimum sintering condition of 1440 °C and 2 h. ZrO₂ particles were homogenously dispersed within matrix grains and at the grain boundaries. The intragranular particles were finer than 100 nm and the intergranular particles were coarser. Both fracture strength and toughness could be enhanced more than two times higher, compare to those of monolithic cordierite, by dispersing 25 wt% ZrO₂ into the cordierite matrix. The toughening mechanism in the present composites was mainly attributed to martensitic transformation due to ZrO₂ dispersion. Electronic Publication