Special features of corrosion-mechanical damage in welded joints in the main heating system of Moscow

Results of investigation of metallographic special features of corrosion damage in longitudinal welded joints of a main heating system with diameters of 1400 mm and wall thicknesses of 40 mm are presented. It is shown that the nucleation of corrosion pits takes place along the fusion line on the internal wall of the heating system in the areas with high hardness (188–223 HV₁₀) and the presence of a large amount of bainite and Widmanstatten ferrite in the structure.     

LaNi5 hydride powder flowability as a function of activation and hydrogen content

Volume expansion of hydrogen absorbing materials, together with inter-particle friction can cause tension accumulation in hydride containers during absorption. When hydride particles absorb hydrogen there is an important volume increase, in the order of 25%. Particles have to accommodate to the container geometry but this movement is opposed by inter-particle friction. Under certain conditions tensions can build up, compromising the mechanical integrity of the container. This phenomenon needs to be addressed at the design stage to avoid mechanical failure of the container.Flow behavior of powder materials is a relevant technological field, usually addressed by means of qualitative or quantitative flowability measuring devices. The rotating drum technique, while mainly qualitative, is well established and can be modified into a completely sealed unit. To determine the flowability of a hydride under different activation stages and hydrogen content levels we developed a rotating drum device that can be pressurized with hydrogen or depressurized. We report particle size evolution and flowability measurements of a hydrogen absorbing material (LaNi₅) at different stages of activation for both absorbed and desorbed states. The results of the present study show that the flowability of LaNi₅ in more dependent on the degree of activation of the sample than on hydrogen absorption state.     

Study of creep cavitation in stainless steel weldment

Abstract

A study of creep cavities near reheat cracking in AISI Type 316H austenitic stainless steel headers, removed from prolonged high temperature operation in nuclear power plants, is reported. It is shown how application of scanning electron microscopy (SEM), cryogenic fractography and small angle neutron scattering (SANS) can be applied, in a complementary way, to observe and quantify creep cavitation. Creep cavities in the vicinity of the crack are found to be mainly surrounding inter-granular carbides. Trends in the size and area fraction of creep cavities relative to the crack path are quantified using optimised metallography. The SANS technique is found to be a very suitable method of quantifying creep cavitation within the size range up to 600 nm averaged over a larger gauge volume. It is shown that the cavity size distribution peaks in the region 100–300 nm, and this correlates closely with the quantitative SEM observations.     

冲击球压技术研究材料局部损伤和弹塑性特征

冲击球压技术是基于赫兹接触理论发展起来的研究材料力学性能的新方法,尽管起步较晚,但是对材料力学性能特征和变化的研究是非常有效的.概述了近40年利用冲击球压技术分析材料局部损伤和评价材料弹塑性特征的理论和研究进展,重点阐述了利用冲击球压技术和赫兹接触理论评价材料恢复系数和动态硬度特征及变化的可行性、敏感性和精确性.结合研究现状对冲击球压技术中隐含的问题进行了划分,并展望了未来冲击球压技术的发展方向.     

Z-fiber influence on high speed penetration of 3D orthogonal woven fiber composites

In the current work we present a computational investigation of high speed penetration response of 3D orthogonal woven fiber composites (3D OWC) utilizing sub-unit cell, meso-level partitioned damage mechanics with the specific aim of understanding the role of Z-fibers in the mechanical response. In our model, two primary sources of nonlinearities have been addressed – one resulting from the strain rate dependence and large deformation of the composite constituents and the other from evolving failure. We reduce a number of arbitrary parameters typically present in high speed models by taking advantage of specific geometrical properties of 3D OWC which prevent extensive delamination. This property allows us to partition the structure into resin impregnated fibers assumed to be wholly responsible for the progressive damage behavior and bulk resin which is identified as the source of visco-plasticity and strain rate dependence. The fibers are modeled as anisotropic linear elastic with strain rate dependent progressive damage evolution. The resin is modeled using an advanced high strain rate large deformation Mulliken–Boyce polymer model (Mulliken and Boyce 2006) together with a terminal thermo-mechanical failure criterion. The projectile is assumed to be cylindrical, isothermal, rigid and impacting at right angles to the plate. The shape of the damaged area and the extent of penetrative damage compares favorably with experiments. We find that Z-fibers aid in improving penetration and impact resistance by both energy absorption and structural engagement. However, we also find that they are susceptible to localized de-bonding especially around the winding crowns. In addition, we found crucial differences in mechanical response in wave propagation brought about by the interplay of fiber architecture and damage with respect to simplified membrane models.Finally, the Z-fibers were found to influence the shape and nature of the damaged area in the fibers compared to layered composites where the matrix damage is spread more evenly while the fiber damage is restricted towards the fiber axes directions.     

The response of the adult and ATD heads to impacts onto a rigid surface

Given the high incidence of TBI, head injury has been studied extensively using both cadavers and anthropomorphic test devices (ATDs). However, few studies have benchmarked the response of ATD heads against human data. Hence, the objective of this study is to investigate the response of adult and ATD heads in impact, and to compare adult Hybrid III head responses to the adult head responses.     

Optical Emission Spectroscopy Study and 3-D Surface Characterization of Silicone Rubber Exposed to Different Argon RF Plasma Powers

Abstract

The present study was undertaken to investigate the effect of argon plasma treatment on the extent of Foley catheter surface modification. Foley catheter (flexible tube made of silicone rubber, used for urinary catheterization) surface was treated at different argon (Ar) RF plasma powers. The surface modification was assessed by measurement of contact angle. Contact angle study shows decrease in contact angle and increase in surface free energy shows more polar group incorporation at low power plasma treatment. Atomic force microscopy (AFM) revealed an increased average surface roughness proportional to plasma power. Optical emission spectroscopy (OES) shows various states of argon causing surface modification.     

防止乘员受挥鞭伤害的汽车座椅设计及试验

针对挥鞭伤害对某车型座椅开发了主动式座椅靠背控制系统(ABCS),同时对座椅骨架和泡沫等结构进行设计优化。经过欧洲新车评价规程(Euro NCAP)挥鞭试验得出结论:主动式座椅靠背控制系统、座椅骨架和泡沫设计优化,均能提高Euro NCAP挥鞭试验成绩,降低对乘员的挥鞭伤害。     

Some Effects of Corona Discharge Treatment of Biaxially-Oriented Polypropylene Film

The effects of the unit corona-treatment energy on the contact angle of various liquids, on the surface free energy, on the extent of oxidation of a surface layer, and on the adhesion of acrylic adhesive were studied using a biaxially-oriented polypropylene (BOPP) film. The surface free energy was determined with the van Oss-Chaudhury-Good (VCG) approach as well as with the wettability method. The extent of oxidation of the surface layer of the corona-treated BOPP film was evaluated with X-ray photoelectron spectroscopy. The adhesion strength of joints between the BOPP film and the acrylic adhesive was measured using the 180°-peel test.

In the range of the unit corona-treatment energy up to 1.2 kJ/m², a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.