Experimental Evaluation of Fracture Surface Energy for Crystalline Dielectric Materials

A physical model is formulated for the reversible initial stage of electrical breakdown that makes it possible to substantiate a method for measuring the fracture surface energy of a thin dielectric layer of metal-dielectric-metal structure at the initial instant of failure.__________Translated from Izmeritelnaya Tekhnika, No. 2, pp. 51–55, February, 2005.     

含半椭圆表面裂纹焊接接头断裂参量的试验研究

本文研究了半椭圆形表面裂纹最深点三维J积分的直接测试技术,并在此基础上,通过对高匹配焊接接头表面裂纹试样断裂力学参量J积分的试验测试,探讨了接头强度匹配对焊接表面裂纹扩展驱动力的影响。试验表明本文所采用的手段对于焊接表面裂纹断裂参量的测试是适用的,且结果也充分反映出焊接接头的力学性能不均匀性的影响作用。     

Measurement of Specific Fracture Energy and Surface Tension of Brittle Materials in Powder Form

Studies of the influence of specimen geometry and size–effect on the K _R –curves and the related fracture parameters were carried out by the authors (Kumar and Barai 2008b). The present paper is a supplementary contribution and reports interesting results related to the effect of the loading condition and size–effect studies on the K _R –curves associated with the cohesive stress distribution for complete fracture process, the double–K fracture parameters, the CTOD–curves and the process zone length using two different loading conditions (i.e., three–point bending test and four–point bending test). The laboratory size specimen with initial–notch length/depth ratios 0.3 and 0.5 are considered in the work. The load–crack opening displacement curves for these loading conditions are obtained using well known version of fictitious crack model.     

重质碳酸钙颗粒气流粉碎与表面改性的一体化处理

研究重质碳酸钙颗粒在气流粉碎与表面改性一体化处理过程中,改性剂溶液流量、改性剂溶液浓度、粉碎气流温度对重质碳酸钙粉出料速度、改性效果以及粒度的影响趋势。研究表明,在气流粉碎的同时进行表面改性处理,可以提高重质碳酸钙粉体的出料速度,选择最佳的粉碎与改性参数后,重质碳酸钙的粉碎出料速率由21.0 g/min提高到56.7 g/min,出料速率提高了170%,并与液体石蜡具有良好的相容性。     

Role of Surface Energy in the Vapor–Liquid–Solid Growth of Silicon

The conditions of vapor-phase Si whisker growth are examined, and the role of the surface Gibbs energy in the vapor–liquid–solid process is evaluated. The mechanism responsible for the catalytic activity of the liquid phase on the tip of Si whiskers is elucidated. Experimental surface tension data are used to estimate the driving force acting on the three-phase line of contact upon a displacement of the liquid droplet in the course of whisker growth.     

粉碎能耗与粒度分布指数的相关性

利用分形和分维数基本概念,导出粉粒度分布的分维数和分裂比、粉碎概率互相存在的简单关系,从能耗与颗粒表面分维数相关出发,推出单位体积粉碎能耗与粒度分布的值指数的相关性;同时推出单位体积粉碎能耗的分维数.当粉碎粒度分布的分维数近似小于0.89时,粉碎能耗呈现自然分形的特征.     

Experimental Analysis of Deposition of Particulates in Confined Spaces

ABSTRACT

Deposition of powders in confined spaces (e.g., dies) is the required first step in manufacturing pressed parts. The quality of the pressed parts is adversely affected by the non-uniform pre-compaction spatial fill density of the particulate in the die. To determine in-situ fill density distribution, a real-time spatial cumulative mass distribution tester incorporating multiple load cells has been designed and fabricated. Preliminary experimental analysis has been carried out for different treatments (die cross-section, rate of die fill, method of die fill, and aspect ratio) for one powder. Data interpretation leads to the inference that both die shape and rate of die filling may be significant factors affecting spatial fill-density distribution. Work is in progress on repetition of identical treatments for five different powders.     

Experimental Verification of the Averaged Strain Energy Density Criterion for Brittle Fracture in Blunt V-Notches under Pure Compression

Strength of Materials - The goal of the present study is to verify experimentally the Averaged Strain Energy Density (ASED) criterion for brittle fracture in blunt V-notches under pure compression....     

Fractal Microstructure of Fracture Surfaces and Fracture Energy of Metals

Using a fractat model, we give a new interpretation of the reversed sigmoidal curves of fracture surface profile length obtained in some experiments. It is pointed out that a single parameter (fractal dimension D) is not sufficient to characterize a fractal curve completely. It is shown that the initiator length L0 is also important to characterize a fractal curve. We have derived a formula which correlate the fracture energy with the fractal parameters of the fracture surfaces and analyzed some experimental data.     

岩石变形破坏过程中的能量传递和耗散研究

岩石变形破坏的过程是和外界产生能量交换的过程。从理论上分析了用能量方法研究岩石破坏问题的合理性,以及岩石在变形过程中弹性能、塑性能、表面能、辐射能、动能之间相互转化的过程、计算原理、以及对岩石破坏所起的不同作用。并分别从宏观和微观的角度研究了在不同的变形阶段中岩石能量耗散与释放问题。在宏观上,岩石变形前期以弹性应变能的方式存储外界提供的能量,同时又通过损伤演化等向外界耗散能量;变形的后期以剧烈的能量释放为主。微观上,存在多种引起岩石应变硬化和应变软化的机制,岩石存储能量还是向外界释放能量取决于这些微观机制竞争的最后结果,基于此推导了岩石变形中能量的传递方程,用试验研究了能量的转化和平衡,以及耗散能和释放能之间的比例关系。结果表明能量耗散导致岩石强度的降低,而能量释放是造成岩石灾变破坏的真正原因。从能量耗散与释放的观点研究岩石的破坏,可以从本质上把握岩石变形和破坏的物理机理,寻找岩石破坏的真正原因,为实际工程提供参考。     

Fracture Energy of Steel Fiber-Reinforced Concrete

Steel fiber-reinforced concrete (SFRC) is a cementitious material reinforced with discrete fibers. The energy absorption capacity is the main material property benefited by fiber reinforcement. Closed-loop servo-controlled equipment should be used to evaluate this property. The tests should be carried out using displacement control in order to obtain the postpeak force- displacement relationship (tensile strain-softening branch). To assess the fracture energy of SFRC, three-point bending tests were carried out using displacement control. Series of notched beams reinforced with 30, 60, and 90 kg/m3 of hooked-end steel fibers were tested. Besides the energy dissipated in fracturing the concrete, the energy determined from the force-displacement relationship can also include the energy absorbed during nonlinear behavior of concrete in compression. Ductile materials, such as concrete reinforced with a high content of fibers, develop large deflections before exhausting their energy absorption capacity. In these cases, the "fixed" points of the bar supporting the displacement transducer may not remain fixed, adding an extra deflection into the control displacement transducer and thus leading to incorrect evaluation of the fracture energy. These factors are analyzed in the present work in order to assess the suitability of the specimen dimensions and the test procedures for evaluating the fracture energy of SFRC.     

密闭空间煤粉爆炸特性的实验研究

为了探明煤粉在密闭空间中的爆炸特性参数,利用20 L球形爆炸装置进行实验测试,实验研究了不同点火能量对煤粉爆炸行为的影响,对比CaCO_3和Al(OH)_3两种惰性介质的抑爆效果及惰性介质的抑爆效力随点火能量的变化规律进行了重点探讨。结果表明:随着点火能量的增加,爆炸压力随着煤粉浓度的增加呈现先上升后下降的趋势,在同一浓度下,粉尘最大爆炸压力和最大升压速率呈线性上升,在高浓度下,粉尘爆炸压力受点火能量的影响更显著;添加CaCO_3和Al(OH)_3能够降低煤粉的爆炸压力,相对于CaCO_3的物理抑爆而言,Al(OH)_3的物理-化学抑爆效果更佳;惰性介质抑爆效力随点火能量增加而下降,建议采用5~10 k J点火能量考察惰性介质对煤粉爆炸的抑制效力。     

泡沫钢填充管的准静态压缩变形模式、力学性能及吸能特性

本工作以430L不锈钢粉为原料,采用粉末冶金法制备泡沫钢,然后通过物理粘结法将泡沫钢芯与薄壁金属管结合,分别对空管和泡沫金属填充管进行准静态轴向压缩实验,并对比分析空管和填充管的压缩变形模式、力学性能和吸能性能.研究表明:在压缩变形过程中,空铝管和泡沫钢填充铝管均呈现轴对称变形模式,而空钢管呈现非轴对称变形模式,泡沫钢填充钢管呈现混合变形模式;泡沫钢填充铝管抗压强度约为56.09 MPa,比泡沫铝填充铝管高1.69倍;泡沫钢填充钢管抗压强度高达116.03 MPa,比泡沫铝填充钢管高1.05倍;当应变量为40％时,泡沫钢填充铝管单位体积能量吸收值为27.93 MJ/m3,是泡沫铝填充铝管吸能值的2.91倍,泡沫钢填充钢管单位体积能量吸收值为35.98 MJ/m3,是泡沫铝填充钢管吸能值的1.15倍;当泡沫钢填充铝管的壁厚由1 mm增大到2 mm时,泡沫钢填充管的平台应力值增大1.36倍;在应变量为40％时,单位体积能量吸收值增大1.26倍,同时泡沫钢填充管在压缩过程中的变形褶皱数随着壁厚的增加而减少.     

三角形菱柱表面积法在材料断面分形维数测算中的应用

分形维数是材料断面特征的定量表征参数之一,同时也是判断材料断裂机理的依据,在材料力学中具有非常重要的意义。为了准确和有效地测算材料断面分形维数,引入三角形菱柱表面积法(TPSAM),并根据其原理编写程序,在Matlab 7.1运行环境条件下实现了该算法,最后采用实例对该算法作了测算。结果表明,该程序简单明了,便于操作;所求算的表面分形维数介于2~3之间,准确度高,可推广使用。     

Relationship between Fracture Toughness and Fractal Dimension of Fracture Surface of Steel

The relationship between fracture toughness and fractal dimension of fracture surface was analysed based on a united fractal model of microscopic fracture modes. It was indicated that fracture toughness is a multivariant function of yield strength, microstructural length, fractal dimension of fracture surface and volume fraction of inclusions, other than a monovariant function of fractal dimension of fracture surface. This new fractal model of fracture toughness was verified to fit well with a set of experimental data of a ultrahigh strength steel with equal microstructure and grain size but different volume fraction of inclusion.     

基于内爆内嵌式测试仪的密闭空间振动测试研究

为研究密闭空间内炸药爆炸产生的振动效应对设备的影响和破坏效果,在密闭爆炸塔内进行TNT爆炸试验,测量内部结构的振动加速度;测试使用内爆内嵌式测试仪,测试仪记录实验数据并回放到计算机。然后分析试验数据,找出结构在不同药量下振动加速度的分布规律,对实验数据进行线性回归,给出总结密闭空间内加速度的计算公式的方法。     

能源计量在节能工作中的重要作用

阐述能源计量在节能工作中发挥的重要作用,明确在能源计量的工作中应强化节能意识、节能的管理以及能源的有效利用,进而把能源计量及节能的认识上升为国家经济安全、国家安全的高度,为建设节约型社会具有十分重要的现实意义.     

Measuring the Size‐Independent Fracture Energy of Concrete

Abstract: The fracture energy of concrete is an important parameter in the analysis of the mechanical behaviour of concrete structures, so it is considered as a material property. However, the most universal test method for measuring the specific fracture energy of concrete (RILEM work‐of‐fracture) has been a subject of intense debate among researchers. The values have been found to vary with the size and shape of the test specimen. In this study, an experimental comparative analysis of the size‐independent fracture energy obtained by two main methods has been carried out. One of these is based on the local fracture energy model of Hu et al. The second is based on the curtailment of the tail of the P–δ curve by Elices et al. Therefore, the relationship between both methods is highlighted. It is shown that both methods give almost identical results.