AN EXPERIMENTAL STUDY ON CEMENT MORTAR SPBCIMENS WITN A CENTRAL SLITS UNDBR UNIAXIAL COMPRESSION

The cement mortar specimens with a central slits are tested under uniaxial com-pression.The test results show that tensile cracks initiate,as a rule near the tip and may propagatesteady for a certain length.Mean while shear fructures appear and propagate slowly to the failurestate in the zone of compressive stress concentration. So the fracture strength of rock under compres-sion might be differentiated into the initial tensile strength,the peak strength and residual strength.     

A FRACTURE MECHANICS ANALYSIS OF FRACTURE PLANE CONTROL IN FRACTURE CONTROL BLASTING

A procedure of fracture control blasting for achieving directional breaking of rocks by blasting is presented. The criterion for initiating of radial cracks in borehole wall under dynamic load and the method for determining the permissible rang of initial gas pressure (p0) in the charge cavity are developed .and the branching of radial cracks and the effeets of the pressure (p0) and blasthole geometry (R0.a.L3) on final dimensions of directed cracks are studied .with Fracture Mechanics analysis in all three aspects of fracture process including crack initiation .crack propagation and crack arrest.     

BAND DAMAGING CRACK MODEL OF CONCRETE

This paper presents a fracture model of concrete,band damaging crack model (BDCM).The BDCM can be used to analyze mechanical behaviour of concrete effectively and easily.Compared with test results;numerical results calculated by the BDCM are very precise.     

STUDY OF SPECIMEN SIZES OF FRACTURE EXPERIMENTS OF CONCRETE MATERIAL

The minimum sizes of specimens that can get effective K_(10) values by 3-point bending, 4-point bending and CT methods are derived on the basis of their notch sensitivity laws and size effect equation of concrete. The results show that the minimum heights of 3-point bending and 4-point bending specimens are very similar to those from Modeer's results, and the minimum height of CT specimen increases as the relative crack length increases.     

DETERMING THE RELIABILITY OF A MEMBER WITH CRACK ACCORDING TO THE INFORMATION FROM FLAW-DETECTION WITH ULTRASONIC WAVE

Using the flaw-detecting with ultrasonic wave one may know the equivalant area of a crack that burys in the member. If the crack is ellipse shaped, the equivalant area is constant, and the distribution function of its major semiaxle and the plane strain fracture toughness of the material are given, then we would get the probability of reliability of the member under the uniform tension. In this condition, a formula of calculating the probability would be provided in this paper. Because a simple and enough precise approximate function has been introduced the formula in the paper is simple in shape and easy to use.     

Three-dimensional modelling of wood fracture in mode I,perpendicular to the grain direction at fibre level

Abstract

A coupled experimental and numerical modelling approach was used to investigate the mechanism of softwood fracture at the fibre level. First, a three-dimensional mixed lattice–continuum fracture model was developed to investigate the mechanism of wood fracture, taking into account the porosity of its structure and its heterogeneities at the fibre level. The critical volumes in the specimen where crack propagation was more probable were modelled by a lattice that could show the alternation of earlywood and latewood fibres, and the other regions were considered as the continuum medium. The proposed model was used to investigate the mode I fracture of a small softwood sample in RL orientation. Secondly, a method was developed for microscopic observation of the crack trajectory and investigating the mechanism of initiation and propagation of cracks. This approach was used for microscopic investigation of the fracture behaviour of spruce specimens in mode I and RL orientation. The results of the numerical study were compared with the experimental results. The prepeak and postpeak behaviour of the obtained stress–displacement curve and also the crack opening trajectory in cross-section and longitudinal section in the model and experiments were in good agreement. Both the model and the microscopic observation showed that in mode I fracture and RL orientation, the main trajectory of the crack propagates in the earlywood ring.     

地下油库岩体裂隙处理及水位动态预测

水封石洞式地下油库是利用地下水的天然埋藏 条件，人工开挖的储油石洞，是洞周围岩体和储存于其中的裂隙水共同组成的储油容器。使储油石在运营期间处于地下水位以下，洞库排水时能保持最小的排水量及最小的水位降落值，且洞库的油品下向外渗漏的关键是如何对姨辶严督写恚⒍粤严洞砗蟮亩纯馇叵滤欢鞒鼋献既返脑げ狻Ｒ曰频旱叵滤馐纯饪馕樯芰嗽诙匝姨辶严都傲阉咎卦诘难芯炕∩希贫ǖ挠庞诠馔     

高温裂缝性凝析气藏压裂技术研究

针对安棚深层系特低孔特低渗高温裂缝性凝析气藏压裂的难点,研究确定了压裂液配方。根据压裂裂缝温度场模拟计算结果,研究了变浓度压裂液优化设计技术,既可保证压裂施工携砂的需要,又可实现压裂液的迅速破胶和快速返排,避免对储层的伤害;研究了在前置液中段塞式加入粉陶降滤技术,解决了压裂过程中砂堵的难题,从而保证压裂效果。通过压裂设计优化及配套斜率式加砂和裂缝强制闭合技术,提高气井的产能。现场应用后取得了明显的增产增储效果,为安棚深层系凝析气藏的开采提供了技术支撑。     

ULTRASONOGRAPHIC DIAGNOSIS OF COXOFEMORAL SUBLUXATION IN HORSES

The clinical and ultrasonographic features of seven horses with coxofemoral subluxation are presented. Affected horses included five adult geldings (11–20 years), one large pony (6 years) and a 3-month-old filly. All were lame at the walk except for the pony with grade 3/5 lameness. Lameness was acute in all horses, but three horses progressed after initial improvement. Crepitus, muscle atrophy, and pelvic asymmetry were inconsistent findings. Ultrasonographic diagnosis of subluxation required dynamic visualization of femoral head displacement from the acetabulum while placing weight on the affected limb and subsequent replacement into its normal position upon limb resting. Acetabular rim fractures and joint effusion were visible regardless of weight bearing status in six horses each. No fractures were identified in the pony; the only patient with a good outcome. Six horses had a poor outcome with severe chronic lameness, four of which were euthanized. Postmortem ventrodorsal radiographs obtained in two horses confirmed subluxation only on extended limb projections, but not on hip-flexed projections. Acetabular rim fractures were not visible radiographically in either horse but were confirmed at necropsy. Subluxation was due to an elongated but intact ligament of the head of the femur in both horses. Osteoarthrosis was evident ultrasonographically, radiographically, and at necropsy. Dynamic ultrasonography was readily performed in the standing horse and produced diagnostic images with a low frequency curvilinear transducer. The apparent poor prognosis for horses with subluxation and acetabular fracture illustrate the importance of this imaging technique to identify affected horses.     

Racecourse fracture management. Part 3: Emergency care of specific fractures

In consideration of first aid of appendicular fractures in the horse, the literature is inconsistent and in some cases wrong or misleading. This in large part is due to misunderstanding of fracture mechanics and this paper aims to give a contemporary review of the subject. It is particularly relevant for fractures that occur on the racecourse or in horses in training which, due to their aetiopathogenesis, have substantial site and configuration commonality. However, the techniques discussed are frequently also applicable to non‐racing injuries. Clinical features are important in assessing horses on the racecourse when imaging techniques are limited. This paper highlights these in order to guide decision making.