岩石Ⅱ型断裂韧度的实验方法

针对纯剪断裂试件存在的问题,提出了采用压剪试件实现岩石Ⅱ型裂纹剪切断裂并测试岩石剪切断裂韧度的实验方法,并通过对压剪试件的应力分布和测试结果的分析讨论,提出了岩石Ⅱ型断裂韧度实验的最佳方案,并进而讨论了Ⅱ型裂纹的两种不同断裂型式和断裂判据。     

脆性岩石高温剪切（Ⅱ型）断裂的微观机理

采用剪切盒和扫描电镜实验研究脆性岩石的高温剪切(Ⅱ型)断裂特征及微观机理,并通过密度、单轴压缩实验研究岩石高温的物性和力学性能.实验表明:在高温加载下,胶结物材料的干脱和岩石内部微裂纹的形成、发育,这两种因素共同影响着岩石的弹性模量、抗压强度、断裂峰值荷载,前者占主导地位起强化作用,后者占主导地位起弱化作用,临界温度为250℃.在高温剪切盒加载下,岩石发生沿原裂纹面断裂破坏,裂纹核随着温度增加而增大,断口多为穿晶断裂.晶面上具有多而密的平行线条纹和较多的岩屑等典型的剪切破坏特征,表明岩石破坏为剪切断裂(Ⅱ型).     

熔合线上含裂纹的不等组配焊接接头裂端场及其断裂参量分析(Ⅱ)

对熔合线上含裂纹的焊接接头，应用有限元方法分析了其模型复合型裂纹的裂纹张开位移（COD）断裂参量与材料组配的关系。结合裂端的位移场的分布，对焊接接头COD断裂参量的分解进行了讨论。更进一步，对不同载荷作用下，熔合线含裂纹焊接接头Ⅰ模型与Ⅱ模型裂纹，即Ⅰ＋Ⅱ型复合裂纹的COD断裂参量的Ⅰ型和Ⅱ型分量DⅠ和DⅡ值进行了数值计算，并对数值解的结果进行了曲线拟合和线性回归，得到了焊接接头的COD断裂参量工程计算方法。     

岩石动态断裂耗能机制的形貌学分析

为研究岩石动态断裂的耗能机制,本文进行了灰岩试样Ⅰ型断裂的快速加载和准静态加载对比试验.对断口进行了激光表面仪扫描和扫描电镜(SEM)拍摄,分别获得了反映粗糙程度和断裂花样的形貌.用分形几何法定量分析了动静态断口粗糙程度,结合SEM图像形貌,指出了动态冲击与准静态断裂断口粗糙程度和断裂模式的差异,讨论了岩石动态断裂的耗能机制.     

脆性材料中倾斜裂纹的断裂评价

以硼玻璃作为典型的脆性材料，实验研究了含倾斜直通裂纹的薄片试样平面受拉时的复合型断裂特性。证明了对于脆性材料的平面应力问题，Ⅱ型应力强度因子对断裂的作用不可忽略，并揭示了平行于裂纹的拉应力对裂纹有闭合作用。这种闭合作用与Ⅱ型裂纹驱动力在一定程度上相互抵消，从而导致一种已被广泛接受的假象：即脆性材料在复合型应力下仅Ⅰ型应力强度因子控制断裂。同时研究也表明，常规的等效裂纹方法评价ＫⅠＣ仅在裂纹斜角小于１５°时近似可用。     

岩石断裂力学测试与理论研究

综合介绍了近几年来，在国家自然科学基金资助下，作者在岩石断裂力学领域内所进行的研究和所取得的部分研究成果，其中包括：试件型式，ＫＩＣ软件系统，加工装置，试件尺寸效应，非线性修正，试件与试验机配匹，复合型断裂，岩石试件Ｋ１的三维边界元计算，岩石动态断裂，岩石断裂面形貌特征的分形理论研究等。     

焊接速度对6005A-T6铝合金双轴肩搅拌摩擦焊接头力学性能的影响

文中研究了转速和热输入特征值WP一定两种条件下焊接速度对6005A-T6铝合金双轴肩搅拌摩擦焊接头力学性能的影响. 结果表明,转速一定时,接头抗拉强度随焊接速度的增加呈先增大后减小的趋势;热输入特征值WP一定时,随着焊接速度的增加,接头的抗拉强度持续减小;接头呈现出三种断裂方式,分别为发生于热影响区的Ⅰ型断裂、发生于焊核区的Ⅱ型断裂和发生于热力影响区的Ⅲ型断裂;Ⅰ型断裂和Ⅱ型断裂为韧性断裂;Ⅲ型断裂为包含韧性断裂和脆性断裂的混合型断裂;接头拉伸断裂位置并非总出现在硬度最低处;焊接速度小于1 000 mm/min时,WP ≤ 1有利于提高接头力学性能,而焊接速度大于1 000 mm/min时,WP > 1更有利于提高接头力学性能.     

岩石断裂韧度的温度效应

对经过１００～６００℃快速热处理的辉长岩和大理岩进行了巴西试验、静态断裂试验和两种温度处理后的冲击断裂试验，结果表明：两种岩方的静态拉伸强度和静态断裂韧度均随热处理温度增加而明显下降；经高温处理后两种岩石的动态断裂韧度随加载率增加而增大，这与未经热处理的情形相似。井借助扫描电镜对岩石的热开裂等现象进行了分析讨论。     

热轧Al-Mg-Mn-Er-Zr合金板材的低温冲击性能

采用夏比缺口冲击试验研究了Al-Mg-Mn-Er-Zr合金的低温冲击性能。结果表明,在-192~0 ℃试验温度范围,随着温度的升高,冲击吸收能量不断降低,而剪切断面率不断上升;Al-Mg-Mn-Er-Zr合金失效方式均以Ⅰ型断裂为主,部分表面显示Ⅱ型剪切断裂特征;在-192 ℃,断口表现出的台阶型断裂特征与Ⅰ/Ⅲ型混合载荷条件下的断裂形貌相似。     

新疆哈密市天宇镍矿特征及成因初探

天宇镍矿位于塔里木板块的两个Ⅱ级构造单元的交汇处,以沙泉子深大断裂为界,西北侧为塔里木板块前缘活动带,东南侧为中天山地块。镍矿体主要分布于杂岩体内部。含矿岩石主要为华力西晚期第一侵入次的纯橄榄岩、辉石橄榄岩、橄榄辉石岩、辉石岩。金属硫化物主要为磁黄铁矿、镍黄铁矿及黄铜矿,次为黄铁矿、白铁矿。多呈半自形-他形粒状、海绵陨铁状。矿石类型以稀疏浸染状为主,其次为稠密浸染状及星散浸染状,准块状-块状、脉状-网脉状。矿床成因类型主要为深部熔离—贯入型,多有后期热液叠加及矿浆贯入成矿作用存在。通过对天宇镍矿地表及深部矿体及岩石的特征、赋矿岩石的岩石化学特征综合分析,天宇镍矿为一岩浆熔离-贯入型硫化镍矿床。     

Micromechanism of Cleavage Fracture of Weld MetalsEI北大核心CSCD

Cleavage fracture is the most dangerous form of fracture. Cleavage fracture usually happens well before general yielding at low nominal fracture stress and strain. Cleavage fracture is often spurred by low temperature and determines the toughness in the lower shelf temperature region. This paper describes a new framework for the micromechanism of cleavage fracture of high strength low alloy (HSLA) steel weld metals. Cleavage fracture not only determines the impact toughness in the lower shelf but also plays a decisive role on the impact toughness in the transition temperature region. The toughness is determined by the extending length of a preceding fibrous crack which is terminated by cleavage fracture. Three non-stop successive stages, i.e. crack nucleation, propagation of a second phase particle-sized crack across the particle/grain boundary, propagation of a grain-sized crack across the grain/grain boundary are explained. The "critical event" of cleavage fracture is emphasized which offers the greatest difficulty during crack formation and controls the cleavage process. The critical event indicates the weakest microstructural component and its critical size which specifies the local cleavage fracture stress sigma(f) for cleavage fracture. In toughness-study it is paramount important to reveal the critical events for various test specimens. Three criteria for crack nucleation, for preventing crack nucleus from blunting and for crack propagation are testified. An active region specified by these criteria is suggested where the combined stress and strain are sufficient to trigger the cleavage fracture. It can be used in statistical analyses. A case study, using the new framework of micromechanism for analyzing toughness of 8% Ni steel welding metals is presented to analyze the experimental results.     

Critical level of intergranular fracture to affect the toughness of embrittled 2.25Cr-1Mo steels

In general, the low-temperature brittle fracture mode of unembrittled ferritic steel is transgranular cleavage. During temper embrittlement, impurity elements, such as sulfur (S), phosphorus (P), antimony (Sb), arsenic (As), and tin (Sn), segregate to prior austenite grain boundaries, which results in a decrease in the grain boundary cohesive strength. As a result, the brittle transgranular cleavage fracture mode changes to intergranular decohesion in association with the decrease in the critical fracture (stress (σ _F) as well as the fracture toughness (K). However, the appearance of intergranular facets on the fracture surface does not cause a decrease in the K and σ _F values. In this work, quenched and fully tempered 2.25Cr-1Mo steel (in an unembrittled condition that exhibits almost 100% brittle transgranular cleavage fracture) has been embrittled for 24, 96, and 210 h at 520 °C to produce different proportions of intergranular fracture. These unembrittled and embrittled steel specimens were tested to measure K (at −120 and −196 °C) and σ _F (at −196 °C). The experimental results and detailed fractographic observations show that the K and σ _F values decrease with an increase in the area fraction of intergranular fracture, provided that the area fraction of the intergranular facet on the brittle fracture surface exceeded a certain critical level, approximately 20–22%.     

基于延性准则的DP800小圆角拉弯成形开裂判据

针对传统FLC无法准确预测超高强度双相钢薄板在较小凸模圆角下拉弯成形时的剪切开裂问题,采用基于延性准则的成形判据计算其应力-应变失效积分因子,结果表明,使用Brozzo和Oyane延性准则计算的失效积分因子在凸模圆角处超过失效单位值,与试验相符,说明Brozzo、Oyan延性准则能够实现小圆角半径下双相钢板材在拉弯成形中的开裂预测。     

Low-temperature fracture toughness of a heat-treated mild steel

Specimens from a 0.14 % C mild steel were austenitized at 1000 °C for 1 h and thereafter furnace-cooled or isothermally transformed at 700 °C for 0.5,2, and 8 h. The microconstituents present in the as-received material were ferrite and pearlite and their amounts did not substantially change even after heat treatment. The impact energy of the as-received and the furnace-cooled materials increased from 4 to 89 J and from 4 to 108 J, respectively, when the temperature was changed from - 196 to 23 °C. For these materials, the failure mode was by ductile fracture at 0 and 23 °C and by quasicleavage fracture at - 196 and - 40 °C. The fracture toughness did not show any significant change with isothermal transformation time at 700 °C. The failure mode of the isothermally transformed materials was always by quasicleavage fracture.     

AZ31B镁合金点焊接头拉剪断裂特征

针对板厚2 mmAZ31B镁合金板材在DZ-3×100三相次级整流点焊机上进行焊接.通过对其焊接接头的拉剪试验、金相显微观察、断口SEM分析、XRD分析,研究了镁合金点焊接头拉剪断裂特征.结果表明,点焊接头拉剪断裂呈现拉剪撕裂和整核断裂两种断裂形式.熔核处断口为韧性-脆性混合型断裂,母材断口处呈现一典型的韧性断裂特征.熔核与母材的物相基本一致.母材焊后,晶界及晶面上析出硬而脆的Mg17Al12金属间化合物,且所占比例远远超过母材基体,熔核区域的断裂倾向增大,Mg17Al12金属间化合物在XRD图谱上衍射峰强.     

Study on fracture behavior of SiCp/A356 composites

The fracture behavior of SiCp/A356 composite at room and high temperatures was studied.Under tensile stress condition at room temperature, the fracture is mostly a combination of the brittle fracture of SiC particles and ductile fracture of A356 matrix.As the tensile temperature increases, the composite changes the main fracture behavior to the separation fracture of the bonding surface between SiC particles and A356 matrix.When the tensile temperature reaches 573 K, the fracture behavior of the composites is almost the whole separation fracture of the bonding surface, which is the main strengthening mechanism at high temperature.Under the cycle stress condition at room and high temperatures, the main fracture behavior of the composites is always a combination of the brittle fracture of SiC particles and ductile fracture of A356 matrix.However, under the cycle stress at high temperature, cycle behavior of the composites changes from cycle hardening at room temperature to the cycle softening at high temperature.     

钢丝杯锥状断口断裂机理

用金相和扫描电镜分析了钢丝杯锥状断口。结果表明,钢丝杯锥状断口形成机理主要是由于钢丝组织中存在夹杂物、组织疏松、碳偏析以及拉拔工艺不当,导致心部出现"V"型裂纹,沿"V"型裂纹断裂后形成杯锥状断口。     

THEORETICAL AND EXPERIMENTAL STUDIES ON FRACTURE PLANE CONTROL BLAST WITH NOTCHED BOREHOLES

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PROBABILISTIC MODELING OF BRITTLE FRACTURE WITH PRIOR DUCTILE CRACK EXTENSION

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