ELASTIC CALCULATION OF STRESSES IN RINGS USING AIRY STRESS FUNCTION

Stress calculation formulae for a ring have been obtained by using Airy stress function of the plane strain field with the decomposition of the solutions for normal stresses of Airy biharmonic equation into two parts when it is loaded under two opposite inside forces along a diameter. One part should fulfill a constraint condition about normal stress distribution along the circumference at an energy valley to do the minimum work. Other part is a stress residue constant. In order to verify these formulae and the computed results, the computed contour lines of equi-maximal shear stresses were plotted and quite compared with that of photo-elasticity test results. This constraint condition about normal stress distribution along circumference is confirmed by using Greens’ theorem. An additional compression exists along the circumference of the loaded ring, explaining the divorcement and displacement of singularity points at inner and outer boundaries.     

Fracture under initial stresses acting along cracks: Approach, concept and results

The problems of fracture under initial stresses acting along cracks in [A.N. Guz’, Mechanics of Brittle Fracture of Materials with Initial Stresses, Naukova Dumka, Kiev, 1983 (in Russian)] is studied. Other approaches and concepts are also briefly discussed. Results for isolated and near-the-surface cracks are given.     

A Practical Application of Ultrasonic Thermal Stress Monitoring in Continuous Welded Rails

A methodology designed to monitor thermally induced loads on continuous welded rails (CWR) is presented. The technique is based on the use of sub-surface longitudinal ultrasonic waves (l.c.r. waves) and, by means of a daily data elaboration, allows to obtain the value of the neutral temperature of the rail as a function of time. From such information an estimation of longitudinal stresses, to be used as a reference, can be derived. The methodology here presented has undergone a 2 years testing period, through the instrumentation of about 3 km of railway track. All acquired data have been remotely processed in a single control station.     

沉积温度对HfO2薄膜残余应力的影响

 用电子束蒸发方法制备了HfO₂薄膜，根据镀膜前后基片曲率半径的变化，用Stoney公式计算了薄膜应力，讨论了沉积温度对薄膜残余应力的影响。结果发现，HfO₂薄膜的残余应力均为张应力，应力值随沉积温度的升高先增大后减小，在280 ℃左右出现极大值。对样品进行了XRD测试，从微观结构上对实验结果进行了分析，发现微结构演变引起的内应力变化是引起薄膜残余应力改变的主要因素，HfO2薄膜在所选沉积温度60~350 ℃内出现了晶态转变，堆积密度随温度升高而增大。     

Influence of Different Factors on the Stiffness and Strength of Multilayer Composite Elements

In the paper, the bending stiffness and strength of multilayer structural elements in relation to the mechanical properties of layers and their number layout and sizes are investigated and the corresponding correlations are established. It is found that the most rational structure of a multilayer element in bending is a symmetric three-layer structure formed from two materials with the thickness of the core less than the half-thickness of the element. The values of normal stresses in the layers of a multilayer beam in bending depends on its bending stiffness and the position of layers relative to the neutral axis. The influence of the number of layers on the stiffness of the structural element and on the magnitude of normal stresses is insignificant.     

The dynamic thermal stresses in hollow cylinder by thermal shock simultaneous with mechanical shock acting on the inner movable boundary

The transient temperature fields and dynamic thermal stress fields in gun barrel are studied in this paper, which are problems of interior ballistics.The high blast temperature and pressure act simultaneously on the inner surface of the barrel behind projectile moving in the barrel during shooting. Under this boundary condition, the governing equations of the thermoelastic problems of hollow cylinder are given, the corresponding functional is studied and the numerical results calculated by the finite element method are obtained.     

Experimental determination of rheological properties of polydimethylsiloxane

A series of linear polydimethylsiloxane of different molecular weight and with reduced polydispersity were prepared by partial fractionation of commercial products. The rheological functions, i.e. zero shear viscosity (η₀), first and second normal stress coefficients (Ψ₁₀ and Ψ₂₀), of the materials were experimentally measured by conventional rotational rheometers and by a rotation rod apparatus. The relationships between molecular structure (molecular weight and polydispersity index) and rheological functions are presented and discussed on the basis of equations proposed in the literature. Zero shear viscosity data conform to the well-known dependence on a power 3.5 of molecular weight. However, a consistently stronger influence of molecular weight over Ψ₁₀ and Ψ₂₀ is found. The influence of polydispersity over Ψ₁₀ is also analyzed.     

Poisson过程作为更新过程的若干新的特征刻画

本文将给出Poisson过程作为更新过程的一系列新的特征刻画．这些刻画是借助于更新过程中所有关键量的条件概率分布或条件期望来表述的．所给的条件是至任一指定时刻发生的抵达敷为已知．     

Numerical and empirical approach in predicting the penetration of a concrete target by an ogive-nosed projectile

This paper demonstrates the application of both numerical simulation and empirical equation in predicting the penetration of a concrete target by an ogive-nosed projectile. The results from the experiment performed by Gran and Frew [In-target radial stress measurements from penetration experiments into concrete by ogive-nose steel projectiles, Int. J. Impact Eng. 19 (8) (1997) 715–726] are used as a benchmark for comparison. In the numerical simulations a 3.0-caliber radius-head steel ogival-nose projectile with a mass of 2.3 kg is fired against cylindrical concrete target with a striking velocity of 315 m/s. The simulation, performed using AUTODYN 2-D, assesses three numerical schemes, namely Langrange, Euler–Lagrange coupling and smooth particles hydrodynamics SPH–Lagrange coupling, in predicting the maximum depth of penetration and the radial stress–time response of the concrete target. When assessing the three solution techniques we hypothesize that the effect of strain rate on strength for the concrete target does not adversely affect the prediction on the maximum depth of penetration and the radial stress–time response of the concrete target. In the empirical approach the penetration equation developed by Forrestal et al. [An empirical equation for penetration depth of ogive-nose projectiles into concrete targets, Int. J. Impact Eng. 15 (4) (1994) 395–405] is used to determine the maximum depth of penetration and the deceleration–time response. The deceleration–time response for the projectile using the empirical approach is compared with those obtained from the numerical simulations. Results from both the numerical and empirical approaches are consistent. The calculated depth of penetration from both approaches yield relatively good agreement with that obtained from the experiment. The numerical simulations using each of the three numerical schemes are also able to reproduce the profiles from the radial stress measurements. Simulations using the SPH numerical scheme give the best overall agreement. The good overall agreement with the experimental radial stress measurements and consistent results between both empirical and numerical approach, enhanced the confidence in engineers and ballisticians when using these two approaches in complementing full-scale testing.