A Bivariate Software Reliability Model with Change-Point and Its Applications

Testing-time when a change of a stochastic characteristic of the software failure-occurrence time or software failure-occurrence time-interval is observed is called change-point. It is said that effect of the change-point on the software reliability growth process influences on accuracy for software reliability assessment based on a software reliability growth model (SRGM). We propose an SRGM with the effect of the change-point based on a bivariate SRGM, in which the software reliability growth process is assumed to depend on the testing-time and testing-effort factors simultaneously, for accurate software reliability assessment. And we discuss an optimal software release problem for deriving optimal testing-effort expenditures based on our model. Further, we show numerical examples of software reliability assessment based on our bivariate SRGM and estimation of optimal testing-effort expenditures by using actual data.

海洋投弃式温深剖面仪应用发展概述

海洋温度的变化会显著影响水下声传播、生物活动、气象和洋流等现象,温深是反映海洋变化运动规律的基本参数。投弃式温深剖面仪(Expendable Bathythermograph,XBT)、温盐深测量仪(Conductivity Temperature Depth,CTD)、全球海洋实时观测网(Array for Real-time Geostrophic Oceanography,Argo)等是目前进行海水温深测量的主要仪器。其中XBT因其现场测量简便、效率高、硬件成本低等特点,正在被大规模使用。本文主要介绍有关海洋温度测量的背景及演化历史,分析对比了国内外相关仪器设备的发展现状,总结了国产化产品还存在的差距和不足,另外对传感器、结构设计、数据通讯传输、数据后处理、可靠性研究等关键技术和研究热点进行了详细介绍,最后对未来无人平台的技术发展路线给出了思路和见解,开展投弃式温深剖面仪的相关技术研究和产品研制对实现国产化有积极的推动意义。

Structures and Properties of Iron Matrix Composites with Tungsten Carbide Particle by EPC-V Process

In this paper the Expendable Pattern Casting with dry sand Vacuum(EPC-V) process is used to manufacture iron matrix composites with tungsten carbide particle.Microstructures of the composites layers were analyzed.The abrasive wear resistance of the composites layers were tested and compared with that of high chromium cast iron.The results show that the iron matrix composites with tungsten carbide particle have high hardness.The abrasive wear resistance of composites with tungsten carbide particle is higher than that of high chromium cast iron.The properties of the matrix materials have been improved remarkably.

Study of the Interface between Steel Insert and Aluminum Casting in EPC

The effective surface treatment method for steel insert composited with Al base metal by expendable pattern casting （EPC） process and the bonding interface between steel insert and Al base metal were investigated.It was found that Zn plating on steel insert was effective on improving the bonding property between steel insert and Al base metal in EPC process.Zn is thought to promote the formation of diffusion layer.But almost none content of Zn was observed in the boundary which had been plated on the steel insert.A diffusion layer consisting of Al,Si and Fe was formed at the insert/alloy interface and its hardness was higher than the steel insert as matter of course Al base metal.This layer turned out to be intermetallic compounds of Al-Si-Fe system.Higher pouring temperature promoted the diffusion of Fe into Al alloy,so Fe content in intermetallic layers increased at higher pouring temperature.The layer nearest to steel disappeared due to applied pressure.

Research on cracking mechanism of the thin shell mould in expendable pattern shell casting during pattern removal process

Aiming at the cracking phenomenon of the thin shell mould in the expendable pattern shell casting during the pattern removing process, some systemic researches are presented.The influence of the pattern removing method and temperature on the pattern removing were investigated.The shell mould cracking mechanism was analyzed by using thermo-gravimetric analysis (TGA), and combining the temperature field and the volume change of the expanded polystyrene (EPS) foam pattern being tested.The results indicated that the shell mould was not easily cracked when the pattern removing process was carried out with the furnace being heated little by little because of the shell slowly shrinking with dehydration and shell strength gradually increasing.The shell mould was soon destroyed when it was set directly into the furnace at above 400 oC because of the thin shell mould rapidly shrinking and the foam pattern hindering.However, the shell mould had no cracking when it had been preheated for a long time even if the furnace temperature was above 400 oC and the shell was put into the furnace directly.Moreover, when the shell mould was directly set into the furnace at lower temperatures, 250 to 300 ℃, the shell would shrink slowly and the foam pattern would stay at the maximum expansion stage temperature of 100 to 110 ℃ for a long time; and the shell mould would experience an expansion force from the foam pattern for a long time.The expansion force is related to the pattern removing temperature, holding time, foam pattern thickness and density.Therefore, the foam pattern with higher density could make the shell crack.

Principles and practice of low pressure-expendable pattern casting process for magnesium alloys

A newly developed low-pressure expendable pattern casting (LP-EPC) process was introduced and its basic principles or effect factors were further analyzed. According to theoretical calculation and experimental results, the major casting parameters that are of great and critical importance on the process include pressure and flux of filling gas, decomposition characteristic and density of foam pattern, thickness and permeability of coating, pouring temperature, vacuum degree and their combination. Most of casting defects can be effectively avoided by choosing the suitable parameters. The success achieved in pouring motor housing and exhaust manifold castings demonstrates the advantages of LP-EPC process in the production of high-complicated castings with high dimension accuracy.

Research on key techniques of expendable conductivity temperature depth measuring system

This paper analysis the developing of expendable conductivity temperature depth measuring system(XCTD)and introduce its principle of measuring about temperature,salinity and depth of ocean.Some key techniques are put forward.According to the real needs of XCTD,conductivity sensor with high sensitivity is designed by principle of electromagnetic induce,the ocean conductivity from induced electromotive force has been calculated.Adding temperature correction circuit would help to reduce error of conductivity measurement because of sharply changing temperature.Advanced temperature measuring circuit of high precision and the constant current source is used to weaken effect of self-heating of resistance and fluctuation of the source.On respect of remote data transmission,LVDS is a good choice for the purpose of guarantee the quality of data transmitted and the transmission distance is reaching to thousand meters in the seawater.Modular programming method is also brought into this research aimed at improve the stability,reliability and maintainability of the whole measuring system.In February,2015,the trials in South China Sea demonstrate that the developed XCTD realize effective measurement at a speed of 6 knots and detection depth at 800 m.The consistency coefficient of the acquired data is greater than 0.99 and the success rate of probe launching is above 90%.

Microstructure and mechanical properties of AZ91D magnesium alloy by expendable pattern shell casting with different mechanical vibration amplitudes and pouring temperatures

To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91 D magnesium alloy were studied.The results indicated that the mechanical vibration remarkably improved the sizes,morphologies and distributions of the primaryα-Mg phase andβ-Mg17 Al12 phase,and the densification and tensile properties of the AZ91 D alloy.With an increase in amplitude,the microstructures were gradually refined,resulting in a continuous increase in mechanical properties of the AZ91 D alloy.While,with the increase of pouring temperature,the microstructures were continuously coarsened,leading to an obvious decrease of the mechanical properties.The tensile strength and yield strength of the AZ91 D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃were 60%and 38%higher than those of the alloy without vibration,respectively.

Novel technologies for the lost foam casting process

Lost foam casting （LFC） is a green precision casting process categorized as a near net forming technology. Yet, despite its popularity, it still suffers from some technological problems, such as poor filling ability of the castings, coarse and non-dense microstructure, low mechanical properties for the A1 and Mg LFC processes, and defective carburization for the low carbon steel LFC process. These drawbacks restrict the development and widespread application of the LFC process. To solve these problems, the present study developed several novel LFC technologies, namely, LFC technologies under vacuum and low pressure, vibration solidification, and pressure solidification conditions; expendable shell casting techno- logy; and preparation technology of bimetallic castings based on the LFC process. The results showed that the LFC under vacuum and low pressure evidently improved the filling ability and solved the oxidization problem of the alloys, which is suitable for producing complex and thin- wall castings. The vibration and pressure solidifications increased the compactness of the castings and refined the microstructure, significantly improving the mechanical properties of the castings. The expendable shell casting technology could solve the pore, carburization, and inclusion defects of the traditional LFC method, obtaining castings with acceptable surface quality. Moreover, the A1/Mg and A1/A1 bimetallic castings with acceptable metallurgical bonding were successfully fabricated using the LFC process. These proposed novel LFC technologies can solve the current technological issues and promote the technological progress of the LFC process.