Transformation Plasticity of Hot-Die Steel During Hardening

The paper presents the results of investigations of transformation plasticity of hot-die steel (high temperature-resistant steel used in high-temperature deforming) during hardening. A special device was used to evaluate transformation plasticity and determine the maximum normal bending stress, modulus of transformation plasticity for medium alloyed and medium carbon steel.     

Fracture strength of flawed cylindrical pressure vessels under cryogenic temperatures

Damage tolerant and fail-safe approaches have been employed increasingly in the design of critical engineering components. In these approaches, one has to assess the residual strength of a component with an assumed pre-existing crack. In other cases, cracks may be detected during service. Then, there is a need to evaluate the residual strength of the cracked components in order to decide whether they can be continued safely or repair and replacement are imperative. A three-parameter fracture criterion is applied to correlate the fracture data on aluminium, titanium and steel materials from test results on cylindrical tanks/pressure vessels at cryogenic temperatures. Fracture parameters to generate the failure assessment diagram are determined for the materials considered in the present study. Failure pressure estimates were found to be in good agreement with test results.     

The stress analysis method for three-dimensional composite materials

This study proposes a stress analysis method for three-dimensionally fiber reinforced composite materials. In this method, the rule-of mixture for composites is successfully applied to 3-D space in which material properties would change 3-dimensionally. The fundamental formulas for Young's modulus, shear modulus, and Poisson's ratio are derived. Also, we discuss a strength estimation and an optimum material design technique for 3-D composite materials. The analysis is executed for a triaxial orthogonally woven fabric, and their results are compared to the experimental data in order to verify the accuracy of this method. The present methodology can be easily understood with basic material mechanics and elementary mathematics, so it enables us to write a computer program of this theory without difficulty. Furthermore, this method can be applied to various types of 3-D composites because of its general-purpose characteristics.     

Investigating Density Distributions for Tablets of Different Geometry During the Compaction of Pharmaceuticals

The axial and radial powder movements during the compaction process were investigated using flat- and curved-face punches for the case of single-ended axial strain applications. The density distributions in microcrystalline cellulose tablets were determined experimentally using a colored layer technique and digital image analysis. Nondestructive topography measurements were taken to assess the variation in surface roughness of the tablets and relate this to the forming pressure and density distribution. Results showed that the tablets produced were highly nonhomogeneous with high density regions in the "top corners" (adjacent to the moving punch surface) and "middle bottom half" for the flat-face tablets. For instance, at 92.7 MPa, density values were recorded at greater than 1.2 g/cc in the high density regions and greater than 0.6 g/cc in low density regions with regards to experimental results. High density regions were noted in the corners where the powder was in contact with the die wall for the curved-face tablets; both axial and radial powder movement was seen to be taking place. Surface topography and surface form results also showed that the geometric location of the corresponding surfaces of the tablets were relocated after the compaction process due to elastic recoil and stress relief.     

Elastic energy in microscopically phase-separated swollen polymer networks

The paper analyzes a microscopic regime of strain, different from the one conventionally considered, that presumably takes place in swollen polymers showing strong microscopic phase separation, such as ion-exchange resins in water. Such systems show linear dependence of the elastic pressure on swelling in contrast to the Flory-Rehner theory and its modifications. The present work proposes a simple model that predicts this kind of behavior. Swelling is considered as a non-affine ‘inflation’ of the hydrophobic matrix by small aggregates of water molecules (‘droplets’) adsorbed by highly hydrophilic groups, whereas the macroscopic dimensions of the sample change as a result of the compression of the ‘films’ separating the droplets. This compression is then analyzed along the classical lines. In the case of the Dowex resins a partial test of the model based on the reported shear moduli showed reasonable agreement with experiment.     

Study of the permeability of thin films of a-Si:H using MeV ion beams

MeV heavy ion irradiation of hydrogenated plasma-deposited silicon nitride induces formation of the volatile molecules H₂ and N₂ inside the material. This type of nitride appears permeable for these molecules and they effuse at relatively low temperature. These effusing molecules are used to study the low temperature permeation in a 100 nm hydrogenated amorphous silicon layer, deposited onto the nitride. Upon irradiation of the double layer stack with 43.3 MeV Ag ions, appearance of D₂ and N₂ from the bottom deuterated silicon nitride layer in the vacuum does not take place up to an ion fluence of 3×10¹² ions/cm². This shows that the 100 nm plasma-deposited hydrogenated amorphous silicon top layer is initially not permeable for D₂ and N₂ molecules.     

Tensor-valued random fields for meso-scale stochastic model of anisotropic elastic microstructure and probabilistic analysis of representative volume element size

The main objective of this paper is to present a generic meso-scale probability model for a large class of random anisotropic elastic microstructures in order to perform a parametric analysis of the Representative Volume Element (RVE) size. This new approach can be useful for a direct experimental identification of random anisotropic elastic microstructures when the standard method cannot easily be applied to anisotropic elastic microstructures. Such a RVE is used to construct the macroscopic properties in the context of stochastic homogenization. The probability analysis is not performed as usual for a given particular random microstructure defined in terms of its constituents. Instead, it is performed for a large class of random anisotropic elastic microstructures. For this class, the probability distribution of the random effective stiffness tensor is explicitly constructed. This allows a full probability analysis of the RVE size to be carried out and its convergence to be studied. The procedure of homogenization is based on a homogeneous Dirichlet condition on the boundary of the RVE. The probability model used for the stiffness tensor-valued random field of the random anisotropic elastic microstructure is an extension of the model recently introduced by the author for elliptic stochastic partial differential operators. The stochastic boundary value problem is numerically solved by using the stochastic finite element method. The probability analysis of the RVE size is performed by studying the probability distribution of the random operator norm of the random effective stiffness tensor with respect to the spatial correlation length of the random microstructure.     

电动轮汽车硅油悬挂装置的研究

车辆的全液压悬挂作为一种新型减振和缓冲装置，具有结构简单，综合工作性能好等优点，本文论述了以甲基硅油为工作介质的全液压悬挂的工作原理，主要技术性能指标，特性曲线的计算机回归及研制工作中的技术攻关情况，并对其工业性试验效果作了详细介绍与评价。     

Mechanical and tribological properties of duplex treated TiN, nc-TiN/a-SiNx and nc-TiCN/a-SiCN coatings deposited on 410 low alloy stainless steel

The use of hard and superhard nanocomposite (nc) coatings with tailored functional properties is limited when applied to low alloy steel substrates due to their low load carrying capacity. Specifically in this work, in order to enhance the performance of martensitic SS410 substrates, we applied a duplex process which consisted of surface nitriding by radio-frequency plasma followed by the deposition of single layer (TiN, nc-TiN/a-SiN_x or nc-TiCN/a-SiCN) or multilayer (TiN/nc-TiN/a-SiN_x, TiN/nc-TiCN/a-SiCN) coating systems prepared by plasma enhanced chemical vapor deposition (PECVD). We show that plasma nitriding gives rise to a diffusion layer at the surface due to diffusion of nitrogen and formation of the α-Fe and ε-Fe₂N phases, respectively, leading to a surface hardness, H, of 11.7 GPa, compared to H = 5 GPa for the untreated steel. Among the TiN, nc-TiN/a-SiN_x and nc-TiCN/a-SiCN coatings, the latter one possesses the highest H value of 42 GPa and the highest H³/E_r² ratio of 0.83 GPa. Particularly, the TiN/nc-TiCN/a-SiCN multilayer coating system exhibits superior tribological properties compared to single layer TiN and multilayer TiN/nc-TiN/a-SiN_x coatings: this includes excellent adhesion, low friction (C_f = 0.17) and low wear rate (K = 1.6 × 10^− 7 mm³/N m). The latter one represents an improvement by a factor of 600 compared to the bare SS410 substrate. The significance of the relationship between the H/E and H³/E_r² ratios and the tribological performance of the nano-composite coatings is discussed.     

Magnetic field sensitive functional elastomers with tuneable elastic modulus

The main purpose of the present work was to establish the effect of external magnetic field on the elastic modulus. We have prepared poly(dimethyl siloxane) networks loaded with randomly distributed carbonyl iron particles. It was found, that the elastic modulus of magnetoelasts could be increased by uniform magnetic field. In order to enhance the magnetic reinforcement effect, we have prepared anisotropic samples under uniform magnetic field. This procedure results in formation of chain-like structures from the carbonyl iron particles aligned parallel to the field direction. The effect of particle concentration, the intensity of uniform magnetic field as well as the spatial distribution of particles on the magnetic field induced excess modulus were studied. It was established that the uniaxial field structured composites exhibit larger excess modulus compared to the random particle dispersions. The most significant effect was found if the applied field is parallel to the particle alignment and to the mechanical stress. A phenomenological approach was proposed to describe the dependence of elastic modulus on the magnetic induction. The magnetic field sensitive soft materials with tuneable elastic properties may find usage in elastomer bearings and vibration absorber.