Effect of specimen geometry on impact strength and ductile-to-brittle transition temperature

Data on the effect of specimen geometry on the ductile-to-brittle transition temperature of low-alloy steel are reported. The influence of the cross-sectional area, specimen width and thickness, notch angle, and root radius were studied.     

Effect of specimen size in determining ductile to brittle transition temperature

Ductile to brittle transition temperature (DBTT) for 9Cr–1Mo steel has been determined from Charpy impact testing for full size and subsized specimens. DBTT was obtained at various percentage of upper shelf energy (USE). Assuming that most of the energy is spent in crack initiation, notch root volumes of subsized specimens (V_NS) were normalised with full size specimen (V_NF), and a power law relationship between DBTT and notch root volume has been established. From finite element method, it is observed that the sum of von Mises stress (σ_eq) and hydrostatic stress (σ_h) reaches ～2400 MPa (fracture stress, σ_f*) as the specimen dimension decreases at a temperature corresponding to 33% USE. This corresponds to ～68 J of full size specimen used in the determination of nil ductility transition temperature.     

Link of the critical temperature of brittleness with the geometry of the stress concentrator and loading rate

It is shown that the critical temperature of brittleness, defined as the temperature at which the critical condition is reached, i.e., local fracture in the tip of the structural stress concentrator, is directly connected with the characteristics of strength, yield, overstrength of the total yield and can be determined by calculation. The proposed approach can be used for developing a method for the determination of the critical brittleness temperature of parts with stress concentrators.Translated from Problemy Prochnosti, No. 12, pp. 35–39, December, 1991.     

A method of determining the critical brittleness temperature of steel from the energy of crack initiation in the specimen

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 5, pp. 51–54, September–October, 1989.     

Effects of specimen geometry on temperature rise and flow behavior of aluminium alloys in hot torsion testing

Inappropriate design of the test specimen in hot torsion testing may lead to a high accumulation of heat in the central region of the specimen gauge length and as a result flow localization may occur. To avoid this, knowledge of the variation of temperature rise due to plastic deformation over the specimen gauge length for different specimen geometries is necessary. It is also necessary to estimate the distribution of temperature rise in the event that heat generation is inevitable so that the constitutive equations used are modified accordingly. This paper is devoted to these points.     

The influence of specimen geometry on crack tip plasticity

The effect of panel width and thickness on the crack tip plasticity of center-cracked fracture panels of 7075-T6 aluminum alloy was examined. The plastic zone formation was continually monitored photographically during the fracture test and the zone size and shape determined by an image distortion technique. The influence of specimen width and thickness was examined to determine its effect on the plastic zone behavior and the mode (stable tear or pop-in) of initial crack extension. Plastic zone models were then compared with the characteristic plastic zone size parameters measured experimentally and the models evaluated. From these results, the effect of panel thickness and width on the fundamental characteristics of crack tip plasticity and initial crack extension was assessed. The importance and implications of these findings on methods of evaluating material toughness are examined. In addition, the applicability of these zone size models in linear elastic fracture mechanics applications are discussed.     

Experimental T33-stress formulation of test specimen thickness effect on fracture toughness in the transition temperature region

This paper describes a study of the test specimen thickness effect on fracture toughness of a material, in the transition temperature region, for CT specimens. In addition we studied the specimen thickness effect on the T₃₃-stress (the out-of-plane non-singular term in the series of elastic crack-tip stress fields), expecting that T₃₃-stress affected the crack-tip triaxiality and thus constraint in the out-of-plane direction. Finally, an experimental expression for the thickness effect on the fracture toughness using T₃₃-stress is proposed for 0.55% carbon steel S55C. In addition to the fact that T₃₃ (which was negative) seemed to show an upper bound for large B/W, these results indicate the possibility of improving the existing methods for correlating fracture toughness obtained by test specimen with the toughness of actual cracks found in the structure, using T₃₃-stress.     

Environmental effect on sclerometric brittleness of ionic crystals

The conditions of plastic-to-brittle transition during microscratching with a Vickers diamond indentor of natural cleavage surfaces of lithium fluoride (LiF) single crystals (pure samples and those covered with octadecylamine films) in heptane, distilled water, and their saturated aqueous solution, were studied. Indentor loads varied in the range 3.2×10^–3-1.9×10^–1 N; indent or sliding velocity was 30 m s^–1. Quantitative characteristics of microplasticity and microbrittleness of near-surface layers in single crystals under appropriate test conditions were studied. The basic mechanisms of crack formation in non-uniform indentor-induced fields of stresses and deformations were revealed and the active media effect on the relative intensity of the functioning of these mechanisms was analysed.     

Proximity effect for superconductors containing transition metal impurities. I

The superconducting proximity effect in a superconductor-normal metal sandwich system in which the metal on the normal side contains dilute 3d transition metal impurities is investigated theoretically. The Kaiser-Zuckermann theory, based on McMillan's tunneling model, is extended by the use of the Hartree-Fock version of the Anderson model to give rise to a bound state in an effective energy gap. For the purpose of analyzing experimental results, the transition temperature and the critical concentration for gapless superconductivity are calculated. It is also demonstrated that with increasing impurity concentration, an impurity band merges into a gap, which may correspond to recent experimental findings.     

Investigation of proper specimen geometry for mode I fracture toughness testing with flattened Brazilian disc method

Investigation of geometrical parameters for flattened Brazilian disc method is important, since this is a simple and attractive method for mode I fracture toughness testing on rock cores. Evaluating numerical modeling results, a parametric equation in terms of principal stresses at the center of the disc and the loading angle of the flattened end was developed. An equation was proposed for maximum stress intensity factors at critical crack lengths around stable to unstable crack propagation. Comparing fracture toughness results of flattened Brazilian disc method to the results of the suggested cracked chevron notched Brazilian disc method, geometrical parameters for flattened Brazilian discs were investigated. Diameter, loading angle of flattened ends, and thickness of andesite rock core specimens were changed to obtain comparable results to the suggested method. The closest results to the suggested method were obtained by 54 mm diameter discs with loading angles larger than 32°, and thicknesses between 19 and 34 mm. Results were confirmed by the flattened Brazilian disc tests on a marble rock. In flattened Brazilian disc tests with smaller loading angles and larger diameters, larger fracture toughness values than the results of the suggested cracked chevron notched were obtained. However, excluding tests with large loading angles over 27°; specimen size was less effective on the results of these tests. Critical crack length parameters computed from modeling and experiments were close to each other for the flattened Brazilian disc specimens with smaller loading angles around 20° and thickness/radius ratio equal or less than 1.1.     

振动特性对颗粒混合均匀性影响的EDEM模拟

应用工程离散单元法(Engineering Discrete Element Method,EDEM)对密闭容器内不同外形颗粒在振动状态下的混合均匀度进行数值模拟,分析振动频率和振幅对粉体混合均匀度标准偏差的影响,并通过正交实验法和方差法对结果进行分析。结果发现:标准偏差随振动时间均表现出递减的变化规律,在6 s之后标准偏差随振动频率的增加呈现减小的变化规律,在4 s之后标准偏差随振幅的增加呈现增大的变化规律,通过正交计算得到振动频率对颗粒混合均匀性影响最大,其次是振幅,综合衡量采用90 Hz、2 mm能获得最佳混合度,通过动态分析颗粒的运动速度验证了正交结果的准确性。     

TiNiHfCu高温形状记忆合金的马氏体相变研究

通过差热扫描分析、X射线衍射和透射电镜等方法研究了Cu的添加对Ti36 Ni49-x Hf15 Cux(x=1,3,5,8)合金马氏体相变行为的影响.研究表明:Cu的加入可稍降低合金的相变温度(约15 ℃),但其Ms仍高于150 ℃,可作为高温形状记忆合金使用;随着Cu含量的升高,合金的B19'马氏体晶格常数a、b和c不发生明显变化,但单斜角β逐渐降低;Ti36 Ni49-x Hf15 Cux(x=1,3,5,8)合金的相组成为B19'单斜马氏体和(Ti,Hf,Cu)2Ni相,马氏体的亚结构为(001)复合孪晶.     

The effect of geometry on three-dimensional tissue growth.

Tissue formation is determined by uncountable biochemical signals between cells; in addition, physical parameters have been shown to exhibit significant effects on the level of the single cell. Beyond the cell, however, there is still no quantitative understanding of how geometry affects tissue growth, which is of much significance for bone healing and tissue engineering. In this paper, it is shown that the local growth rate of tissue formed by osteoblasts is strongly influenced by the geometrical features of channels in an artificial three-dimensional matrix. Curvature-driven effects and mechanical forces within the tissue may explain the growth patterns as demonstrated by numerical simulation and confocal laser scanning microscopy. This implies that cells within the tissue surface are able to sense and react to radii of curvature much larger than the size of the cells themselves. This has important implications towards the understanding of bone remodelling and defect healing as well as towards scaffold design in bone tissue engineering.     

The characteristic research on the flame retardant of calcification foam on the high temperature coal

The coal spontaneous combustion is an urgent issue to be solved for the mine safety production. In the present paper, a new flame retardant of the calcification foam is proposed to improve the prevention effectiveness on the high temperature coal. The molecular dynamics simulation shows that the calcification foam exhibits a superior water retention performance at the thermal environment than the original foam. Ca²⁺ enters the hydration layer of the calcification foam and expands the head groups distance by 22.27%. Ca²⁺ focuses on the second hydrated water shell around the head groups and restricts the water molecule drainage. The drainage rate decreases with the temperature rise according to the diffusion coefficient. The oil bath experiment explains that the drainage rate of the calcification foam is slower and the growth rate is only half of the original foam at 100–150 °C. The calcification foam successfully restrains the coal spontaneous combustion. The coal heating rate treated by the calcification foam decreases obviously and the maximum reduction of CO release achieves 60%. The calcification foam has a good plugging and water retention properties for coal with the average inhibition rate up to 75.36%. The calcification foam has a superior effectiveness on suppressing the flame development.     

The effect of specimen thickness and temperature on plastic yielding and fracture properties of mild steel

The effect of thickness and temperature on deformation and fracture behavior is investigated in notched bend specimens of mild steel in low temperature region using a photo-elastic coating technique. The plastic constraint factor is determined and compared with the theoretical value obtained by slip line field theory. The difference of general yielding properties between surface and interior of specimen is examined by the observation of yield propagation. From these results, a qualitative picture of distribution of σ_z (the stress of thickness direction) is deduced. The effect of thickness on the plastic constraint factor and the plastic stress concentration factor R at T_GY (the critical temperature at which general yielding and fracture coincide) is discussed and so-called “thick specimen” is defined in cleavage fracture region. Then, the thickness effect on twin formation is studied. It becomes clear that the critical temperature T_t above which no twins are formed can be determined by the constant value of the plastic constraint factor. Finally, the relation between the plastic constraint factor, specimen thickness and temperature is embodied by the three dimensional diagram and the condition of plane stress is pointed out.