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The mechanism and criterion of crack initiation and propagation of rocks were investigated by many researchers,And the creep behaviour of rocks was also theoretically and experimentally studied by some scientists and engineers.The characteristics of crack initation and propagation of rocks under creep condition.however,are very improtant for rock engineering and still not paid enough attention by researchers,In this paper,the criterion and mechanism of crack initiation and propagation under creep condition were investigated using specimens collected from sandstone rock formations outcropping in the Emei Mountain,the Sichuan Province of China.Cuboid specimens under three point bending were used in this investigation.All specimens were classified into four sorts and used for Mode-I fracutre of creep frcture tests.The experimental result shows that due to creep deformation.rock crack will inevitably initialt and propagate under a load of KI,which is less than fracture toughness KIC but not less than a constant(marked as KIC2),KIC2 indicates the ability of rock to resist crack initiation and propagation under creep conditions and is less than fracture tough ness KIC.defined as creep fracture toughness in this paper,KIC2 should be considered as an importnat parameter on design and computation of rock engineering.The microstructureal mechanism for crack initiation and propagation of rock materials under creep condition was introduced based on competitive model between softening effect and hardening effect,and the validity of test result was explained.The test result was also verified in rheological theory.When KI is more than KIC2 but less than KIC,rock crack will initiate and propagate after a time interval of sustained loading under creep condition.In order to find the relation between duration of sustained lading.which can lead to crack initiation and propagation,and the initial stress intensity factor KI,an unequal0interval time sequence forecasting and predicting model was introduced,and the relation was obtained for homogeneous and isotropic fine-grained red sandstone.Finally a modified fracture toughness formula was given,in which the influence of fracture process zone(FPZ) was fully considered. 相似文献
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陈有亮 《南京广播电视大学学报》1997,(1)
组织学生参加社会实践和生产实习是实践性教学环节的需要,也是培养学生应用能力,提高综合素质的重要措施。近年来,南京电大直属部根据电大的培养目标和规格,在组织学生社会实践活动中取得了较好的效果,受到了师生和社会各界的好评。在社会实践活动中,我们着重抓了以下几方面的工作: 一、组织学生参加社会实践活动,教育学生树立全心全意为人民服务的思想,激发学生的爱国主义热增。 相似文献
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鸭蛋清酶水解及其水解物对免疫功能的影响 总被引：1，自引：0，他引：1
用碱性蛋白酶和动物蛋白水解复合酶水解经酒精酵母脱糖后的鸭蛋清,并用正交试验确定了动物蛋白水解复合酶的最佳水解条件.结果表明,鸭蛋清浓度5%,动物蛋白水解复合酶用量(E/S)0.7%,pH8.0,反应温度54℃,反应时间4 h时水解效果最佳,水解度达92.65%.其水解物无需脱苦、脱盐和脱色.动物试验表明蛋清水解物能显著提高小鼠红细胞C3b受体花环率.而其红细胞免疫复合物花环率没有显著变化.说明蛋清水解物能在一定程度上增强小鼠红细胞免疫功能. 相似文献
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酪蛋白磷酸肽的功能及其制备 总被引：2，自引：0，他引：2
酪蛋白磷酸肽是从牛乳酪蛋白中水解分离所得的一种生物活性肽,具有很强的促钙吸收活性。本文就酪蛋白磷酸肽的结构、功能、制备、理化性质、检测等进行了系统的概述。 相似文献
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陈有亮 《南京广播电视大学学报》2002,(3):49-50
“后进生”这种提法是否妥当待商洽,但我认为“后进”的学生确实存在。本文所说的所谓“后进生”是指一些思想品德不纯、行为习惯较差、学习成绩较差又不愿努力的学生。这些学生人数不多,但在班级中能量较大,他们自己不愿学习,还常常搅得老师无法上课,同学无法学习,有的 相似文献
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将酱牛肉在乳酸链球菌素、乳酸钠、山梨酸钾、双乙酸钠和柠檬酸配成的复合保鲜液中浸泡后真空包装,在7℃下贮存,以菌落总数作为保鲜效果的指标.以四元二次旋转组合设计探讨乳酸链球菌素、乳酸钠、山梨酸钾和双乙酸钠的交互作用及最佳配比.结果表明:单因子抑菌效果排序依次为乳酸链球菌素、乳酸钠、山梨酸钾和双乙酸钠,乳酸链球菌素与乳酸钠、乳酸链球菌素与山梨酸钾存在显著的交互效应,保鲜剂最佳添加量分别为乳酸链球菌素0.1460 g/kg,60%乳酸钠14.55 g/kg,山梨酸钾0.0684 g/kg,双乙酸钠2.084 g/kg. 相似文献