Numerical calculation of energy release rates by virtual crack closure technique

A seamless analysis of material behavior incorporating complex geometry and crack- tip modeling is one of greatly interesting topics in engineering and computational fracture mechanics fields. However, there are still large gaps between the industrial applications and fundamental academic studies due to a time consuming detailed modeling. In order to resolve this problem, a numerical method to calculate an energy release rate by virtual crack closure technique was proposed in this paper. Both free mesh method and finite element method have been utilized and, thereafter, robust local and global elements for various geometries and boundary conditions were generated. A validity of the proposed method has been demonstrated through a series of fracture mechanics analyses without tedious crack-tip meshing.     

Consideration of the frictional force on the crack surface and its implications for durability of tires

In order to find out a physical quantity which controls the fatigue life of a structure and to predict the fatigue life of tires, a finite element simulation methodology to use the cracking energy density (CED) and the virtual crack closure technique (VCCT) was proposed and applied to three different tires of a similar size. CED was calculated to predict the location of a crack initiation, and VCCT was used to obtain the strain energy release rate (SERR) at the tip of an initiated crack. Finite element simulations showed that SERR oscillated in the circumferential direction with its minimum occurring just before the contact zone and its maximum occurring just after the center of the contact zone, and SERR was affected significantly by the frictional force acting on the crack surface. In addition, a durability test was conducted to measure the fatigue life of the three tires. The comparison of SERR values with the test data revealed that the fatigue life increased as the amplitude of SERR decreased or as the R-ratio of SERR increased.     

A simple method to calculate mode components of strain energy release rate of free-edge delaminations in composite laminates

A simple method, which calculates the mode components of the strain energy release rate of free-edge delaminations in the laminates, is proposed. The interlaminar stresses are evaluated as an interface moment and interface shear forces that are obtained from the equilibrium equations at the interface between the adjacent layers. Deformation of an edge-delaminated laminate is calculated by using a generalized quasi-three dimensional classical lamination theory developed by the author. The analysis provides closed-form expressions for the three components of the strain energy release rale. The analyses are performed on [+30/−30/90]s laminates subjected to uniaxial extension, with free-edge delaminations located symmetrically and asymmetrically with respect to the laminate midplane. Comparison of the results with a finite element solution using the virtual crack closure technique shows good agreement. The simple nature of this method makes it suitable for primary design analysis for the delaminations of composite laminates.     

An experimental and mathematical study on the effects of ignition energy and system on the flame kernel development

A constant volume combustion chamber is used to investigate the flame kernel development of gasoline air mixtures under various ignition systems, ignition energies and spark plugs. Three kinds of ignition systems are designed and assembled, and the ignition energy is controlled by the variation of the dwell time. Several kinds of spark plugs are also tested. The velocity of flame propagation is measured by a laser deflection method, and the combustion pressure is analyzed by the heat release rate and the mass fraction burnt. The results represent that as the ignition energy is increased by enlarging either dwell time or spark plug gap, the heat release rate and the mass fraction burnt are increased. The electrodes materials and shapes influence the flame kernel development by changing he transfer efficiency of electrical energy to chemical energy. The diameter of electrodes also influences the heat release rate and the burnt mass fraction.     

车辆液压储能传动能量转化元件的匹配分析

针对具有特殊运行工况的城市公交车辆,研究一制动能量回收与再利用系统,以期改善车辆的燃油与环保性能,该装置采用高、低压蓄能器、二通插装法、可逆变量泵-马达等部件。介绍了车辆液压储能传动的组成和工作原理。分析了系统中关键元件之一能量转化元件—变量泵/马达排量的确定方法,推导了确定变量泵/马达排量的计算公式,并以某型公共汽车为例,通过分析计算得出了系统的能量回收率与变量泵/马达排量的关系,为车辆液压储能传动系统合理匹配变量泵/马达提供了依据。     

Measurement of strain rate sensitivity of aluminium foams for energy dissipation

In this paper the structural performance of aluminium alloy foams have been investigated under both static and dynamic compression loads. Three foam typologies (M-PORE, CYMAT, SCHUNK) in a wide range of density (from 0.14 to 0.75 g/cm³), made by means of different process-routes (melt gas injection, powder metallurgy, investment casting) have been analysed. Foams microstructural characterization has been carried out through morphometric measurements by means of Scanning Electron Microscopy (SEM) and Computed Tomography (CT) and subsequent digital image processing in order to determine average cells size and cell distributions on different section planes. The experimental study aims to assess the strain rate sensitivity and energy absorption capability of commercially available metal foams and to point out the correlation between the mechanical behaviour and the physical and geometrical properties of the foam. It has been found that the specific energy dissipation of foams with similar density can be quite different: for the same volume of foam, average values of 1770, 1780 and 5590 J/kg at 50% nominal compression have been measured on M-PORE (0.19 g/cm³), CYMAT (0.28 g/cm³) and SCHUNK (0.28 g/cm³) foams, respectively. Impact tests showed that the dependence of the plateau stress on strain rate could be considered negligible for M-PORE and CYMAT foams while it is quite remarkable for SCHUNK foams. Moreover, it was found that the peak stress of CYMAT foams has a quite large sensitivity on the loading rate.     

IC卡式热能表充值系统的设计

IC卡式热能表充值系统是专用于IC卡式热能表充值管理的系统，本文从整体上介绍了IC卡式热能表充值系统的设计过程，设计包含读卡器和安装在PC机上的充值系统软件两部分的设计，并选用RS232 Modbus协议作为读卡器和PC机之间通信方式。     

The experiments for the enhancement of regression rate of hybrid rocket fuel

Many studies have been conducted to increase regression rate of solid fuel in hybrid rocket. One of them resorts to swirl flow since it can extend the residence time of oxidizer in the fuel grain. Also, metal wires may lead to increase the regression rate of solid fuel as shown in solid propellants. In this study, a series of experiments was designed to investigate the enhancement of regression rate of solid fuel by embedded metal wires and by fuel port grain. And fuel port was designed with a helical configuration to attempt to induce swirl flow. PMMA with gaseous oxygen is the solid fuel used for investigation. Test results showed that embedded metal wires turned out to be ineffective method because only 3-4% increases in regression rate were observed. However, fuel port grain configuration yields higher burning performance of up to 50% increase in regression rate. Also pitch number as well as total impulse was found to be a design variable.     

虚拟仪器技术在敏感元件测试系统中的应用

结合国家重点“九五”科技攻关项目“一体化厚膜高分子温湿度传感器”测试系统的研制，将虚拟仪器技术思想应用在整个开发过程，提出相应的硬件和软件设计结构，并且为虚拟仪器技术思想在诸多测试系统中的应用提供了良好的佐证。     

面向敏捷供应体系虚拟企业的建造

针对机床企业提出一种面向敏捷供应体系的虚拟企业模型，分析了机床行业虚拟企业模型的特．点、面向敏捷供应体系虚拟企业实施的前提条件和原则，最后给出面向敏捷供应体系虚拟企业的建立流程。     

Theoretical study of adhesion energy measurement for film/substrate interface using pressurized blister test: Energy release rate

In this paper, a new loading method able to subtly control the crack driving force for pressurized blister test was proposed. A theoretical study of the adhesion energy measurement for film/substrate interface using this loading method was presented. Problems considered include solving the exact volume under a circular blister and the elastic strain energy stored in a thin blistering film, determining the work done by the poured colored liquid as external force to the system and the elastic strain energy stored in the compressed air. A new formula of energy release rate was finally presented. A comparison between the work presented here and the existing work was made.     

The sensitivity analysis of yaw rate for a front wheel steering vehicle: In the frequency domain

In this paper, the sensitivity analysis of yaw rate for a front wheel steering vehicle is performed in the frequency domain. A two degree of freedom system is used to represent a simple vehicle model in order to derive the system transfer function. The transfer function is defined between a steering angle input and a yaw rate output. This model shows the simplest lateral dynamic effect and is useful for understanding of the dynamic characteristics and control aspect of the target system. Vehicle mass, inertia, cornering stiffiness, and wheel base are selected as design variables. Sensitivity functions of the transfer function with repect to design variables are derived, and the results show that the response of the yaw rate always has stable minimum phase characteristics. The objective of this paper is the proposition of a base for re-design and new-design of the vehicle by checking the yaw rate variations with respect to the design variable change in the frequency domain. Finally, dominant design variables can be selected based on the sensitivity analysis.