Papers by Keyword: Low Stress

Abstract: P91 heat-resistant steel is widely used in the high temperature of piping components of thermal power plants and nuclear power plants. In these conditions, the typical failure of P91 is mainly caused by creep at low stress. In this investigation the short-term creep behavior in P91 at low stress was investigated by helicoid spring creep test due to its high strain-sensitivity. The helicoid spring creep was based on the assumption of pure torsion. The mechanics field was firstly studied by ANSYS finite-element simulation to find the establishing conditions of pure torsion. Secondly, the creep properties of P91 were studied under the conditions of the temperatures of 0.38T_m<T<0.46T_m and the stresses of 14.6 MPa, 25 MPa, 34 MPa, respectively. The ANSYS finite-element simulation shows that the creep deformation is considered to be pure torsion when the pitch spacing of coil is between 2mm to 4mm. The creep curves show "Normal type ", and “the stress exponent” is n=0.9.

Abstract: This paper studied the mechanical behavior of composite yarn fabrics and pure cotton yarn fabrics with the conditions of small deformation, then making some comparison. KES-F (Kawabata Evaluation System for Fabric) system was used in the research process. The study shows that the fabric samples made of composite yarn exhibit noticeable improvement on mechanical property after using composite yarn. The results lay a solid foundation for the application and extension of composite yarn fabrics.

Abstract: The research use an impact test enginery, choose T10 steel samples, and do a low stress repeated impact collisions experiment. By comparing two kinds of different heat treatment of T10 steel, analyze and research its macro plastic deformation phenomena and plastic accumulation law in low stress repeated collision impact load, and observe its hardness change by hardness microscopicand and its metallographic structure by metallographic microscope to discuss its deformation causes.

Abstract: 1Cr18Ni9Ti specimens were observed the plastic deformation by the method of coordinate grid under the low stress repeated impact test. And it found some phenomenon is similar to the creep phenomenon ,so the paper call it “repeated impact creep”. Proceeding from the theory of creep deformation, the deformation law of the specimens was analyzed and the relevant mathematical model was established.Finally, it found that the strain rate of repeated impact creep is decreased by the increase of impact times and the increase of layer’s depth.

Abstract: Low stress repeated impact experiments and test were carried out on medium carbon steel and stainless steel samples which is clad with high-strength Co-based or Ni-based alloy. The results showed that under low stress repeated impact load, which is much lower than the yield strength of material, plastic deformation will be occurred on the coating and part of its below base material. The average plastic deformation degree caused by each impact is increased at first, and then declined with the increase of impact times. Accumulated impact will lead to macroscopic plastic deformation and material hardening. The degree of deformation and the size of deformation area are related to the impact stress value and the material’s strength. The degree of deformation and hardening decline from the exterior to the interior, and only occur on the impact surface and a certain depth below, forming a ‘deformable area’. Based on our analysis, we consider that low stress repeated impact deformation is a kind of accumulative fatigue damage. The energy absorbed by material under repeated impact load, is larger than that absorbed at the same peak value of stress under static load or static fatigue load. Moreover, the energy absorbability is inversely proportional to the impact distance. Repeated impact may increase the movability of atom, reduce the critical shearing stress, that make the dislocation be initiated and increased easily.

Abstract: The standard Local Oxidation of Silicon (LOCOS) technique uses different oxidation rates of silicon and Low Pressure Chemical Vapour Deposited (LPCVD) silicon nitride in steam ambient to structure the field oxide. Due to different coefficients of thermal expansion a pad oxide is needed at the boundary layer to prevent stress from the substrate. This leads to a lateral diffusion of oxygen, also known as “birds beak”, which limits the minimum structure size to a few 100 nm [1]. When scaling down to this dimension, the Shallow Trench Isolation (STI) has become the standard isolation technique for fabrication of high-performance semiconductors to allow a high package density. Unfortunately the STI-process uses Chemical Mechanical Polishing (CMP) which increases the process complexity and leads to high costs. Therefore a new method which uses a low stress Plasma Enhanced Chemical Vapour Deposited (PECVD) silicon nitride without a pad oxide at the boundary layer will be presented in this paper.

Abstract: This paper reviews a new, low-temperature process for soldering and brazing ceramics to metals that is based on the use of reactive multilayer foils as a local heat source. The reactive foils range in thickness from 40μm to 100μm and contain many nanoscale layers that alternate between materials with large heats of mixing, such as Al and Ni. By inserting a free-standing foil between two solder (or braze) layers and two components, heat generated by the reaction of the foil melts the solder (or braze) and consequently bonds the components. The use of reactive foils eliminates the need for a furnace, and dramatically reduces the heating of the components being bonded. Thus ceramics and metals can be joined over large areas without the damaging thermal stresses that are typically encountered when cooling in furnace soldering or brazing operations. This paper draws on earlier work to review the bonding process and its application to a variety of ceramic-metal systems. Predictions of thermal profiles during bonding and the resulting residual stresses are described and compared with results for conventional soldering or brazing processes. The microstructure, uniformity, and physical properties of the reactive foil bonds are reviewed as well, using several different ceramic-metal systems as examples.