A DISCUSSION ON SAFTY EVALUATION OF PRESSURE VESSELS

Based on the experience obtained in safty evaluation of pressure vessels, points for attention in the evaluation work are pointed out, problems concerning the present criterion of evaluation are discussed, and meanwhile safty evaluation is done for a pressnoe vessel in service, with satisfactory results.     

Indentation Cracking Mechanical Analysis of ZrO2 Laminated Ceramics

The formation of indentation cracking has some relationship with the transformation stress induced by martensitic transformation, besides the relationship with the residual stress by volume change in the plastic zone in ZrO_2 laminated ceramics. Whereas surface residual compressive stress controls the expansion of surface cracks. Contributions of the transformation driving force and surface compressive stress are not considered in the traditional indentation theory. Therefore, fracture toughness value measured by the traditional method is usually lower than the practical one in ZrO_2 laminated ceramics. When indentation-fracture method is used, the value is more reliable.     

THE DIRECTING MECHANISM OF V-NOTCHF WITHJN V-NOTCHJNG BLASTING

Based on the blasting theory and "Fracture Mechanics " , the directing effect mechanism of V-netch in V-rotching blasting is studied and the positive splitting and directional explanding of crack within V-notching blasting and the priority of crack's expanding in the V-notch axle-plane etc are expounded. It's just these fracture characteristics mentioned above that ensure the fine control of the cracking plane.     

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.     

低渗透裂缝性油田复合射孔注水技术研究

红岗北油田于2004年底投入开发,由于存在东西向天然微裂缝,造成东西向油井暴性水淹。对常用油层改造方法适用范围进行分析对比后,确定采用复合射孔技术,对注水层段进行改造。根据油层发育状况不同,采用变参数射孔技术,并且增加脉冲次数,从而提高油层渗透率;另外,通过控制注水压力在裂缝启动压力之下,确定东西向油井合理穿透率,进一步降低了注入水沿裂缝推进的机率。应用后东西向油井暴性水淹得到了有效控制,采收率提高5%左右。     

Bone fatigue and its implications for injuries in racehorses

Musculoskeletal injuries are a common cause of lost training days and wastage in racehorses. Many bone injuries are a consequence of repeated high loading during fast work, resulting in chronic damage accumulation and material fatigue of bone. The highest joint loads occur in the fetlock, which is also the most common site of subchondral bone injury in racehorses. Microcracks in the subchondral bone at sites where intra‐articular fractures and palmar osteochondral disease occur are similar to the fatigue damage detected experimentally after repeated loading of bone. Fatigue is a process that has undergone much study in material science in order to avoid catastrophic failure of engineering structures. The term ‘fatigue life’ refers to the numbers of cycles of loading that can be sustained before failure occurs. Fatigue life decreases exponentially with increasing load. This is important in horses as loads within the limb increase with increasing speed. Bone adapts to increased loading by modelling to maintain the strains within the bone at a safe level. Bone also repairs fatigued matrix through remodelling. Fatigue injuries develop when microdamage accumulates faster than remodelling can repair. Remodelling of the equine metacarpus is reduced during race training and accelerated during rest periods. The first phase of remodelling is bone resorption, which weakens the bone through increased porosity. A bone that is porous following a rest period may fail earlier than a fully adapted bone. Maximising bone adaptation is an important part of training young racehorses. However, even well‐adapted bones accumulate microdamage and require ongoing remodelling. If remodelling inhibition at the extremes of training is unavoidable then the duration of exposure to high‐speed work needs to be limited and appropriate rest periods instituted. Further research is warranted to elucidate the effect of fast‐speed work and rest on bone damage accumulation and repair.     

Bilateral traumatic optic nerve avulsion in a Thoroughbred gelding

This report describes an unusual case of acute blindness following traumatic head injury in a mature horse. The horse fell over backwards and subsequently presented with bilateral blindness and epistaxis. Vision did not return following medical supportive therapy and euthanasia was elected. Post mortem findings revealed a basisphenoid fracture and bilateral optic nerve avulsion rostral to the optic chiasm, an uncommon presentation of traumatic blindness not previously reported in the horse.