白点的判据方法研究

最近几年,由于诸多原因,有时在盘环件低倍检验试样面上发现白点裂纹,低倍断口与力学性能检验结果均正常.取试样复验,低倍白点裂纹及断口白亮斑时有时无,裂纹性质难以确认.采用调质断口、缓慢拉伸、金相及蚀坑四种方法对疑白点裂纹的判定方法进行了研究.结果表明虽然调质断口法能判定白点,但是确认率不高;缓慢拉伸法不仅能判定白点,而且还能表明材料的原始状态且准确性较高;金相法是判定白点缺陷的一种简便方法;蚀坑法能反映白点断裂的晶体学取向关系,是研究白点判据的一种辅助手段.     

Al2O3-40%TiO2陶瓷涂层残余应力的有限元分析

为分析大气等离子喷涂Al2O3-40%Ti O2复合陶瓷涂层在冷却过程中涂层崩裂的现象,本文采用有限元方法,研究了涂层内部残余应力分布情况,探讨了涂层厚度、孔隙、裂纹等因素对残余应力的影响。结果表明:基体与粘结层和粘结层与涂层的界面边缘处出现了应力集中区域,随着X尺寸(模型水平方向的距离)的增加,涂层及粘结层内部应力由压应力转变为拉应力;涂层厚度只对残余应力值有影响,对应力分布状态影响较小,随着涂层厚度的增加,X向(径向)应力逐渐增加,Y向(轴向)应力及剪切应力在界面边缘处急剧变化;大孔隙、纵向裂纹对涂层残余应力影响较大。有限元模拟分析较好的解释了涂层在冷却过程中涂层层状崩裂的现象。     

棒材三辊减定径机组辊环、轴套装配分析

分析棒材三辊减定径机组辊环、轴套检测方法、装配温度、工作力矩和工作应力,根据分析结果对辊环和轴套的装配和使用进行指导。     

缓慢拉伸法在确认低倍白点中的应用

针对盘件低倍检验试样表面上发现的白点裂纹,低倍断口与力学性能检验结果正常。通过缓慢拉伸法及其断口的宏观、微观分析,确认低倍裂纹为白点裂纹。     

铁素体钢中白点缺陷的检验分析

 通过金相显微镜、扫描电镜等分析方法对铁素体钢低倍检验后发现的疑似白点缺陷进行了分析判断,发现疑似白点缺陷在金相显微镜下呈锯齿状裂纹,为白点裂纹形貌特征。通过对低倍试样上断口的检验发现,低碳铁素体钢宏观断口处分布有银灰色圆形斑点,为白点缺陷特征,铁素体不锈钢宏观断口无明显白点特征,但铁素体不锈钢的疑似白点显微断口有沿晶断裂和以夹杂物为裂纹源的解理断裂两种,都具有氢脆断口特征,由此判断,两种铁素体钢中缺陷均为白点缺陷。铁素体不锈钢中的白点缺陷与常见白点断口上的浮云状、波纹状、解理羽毛、显微疏松等形貌特征有所不同,而且不同铁素体不锈钢试样上的白点缺陷断口形貌也不同,一处为沿晶断裂,一处为以夹杂物为裂纹源的解理断裂。     

线材减定径机辊环在轧制过程中的应力状态及开裂原因分析

针对线材减定径机辊环的使用工艺状况,采用有限元方法分析轧制过程中的应力状态,探讨辊环产生裂纹的原因。减定径机辊环在轧制中的应力状态呈两向压应力和一向拉应力,沿孔槽的等效应力值分布从槽底向槽口逐渐减小,且不同孔型形状和孔型充满率沿孔槽的应力分布变化不同。由于其特有的孔型形状和不同于椭圆孔、圆孔的应力值分布,扁圆孔(Lemon孔)辊环极易产生裂纹甚至开裂。     

高速线材轧机辊环装配工艺研究

辊环装配设计既要满足轧制力矩传动的下限条件，又受到辊环强度的上限条件限制，设计计算要求较高精度。针对辊环装配设计的特点，运用弹性力学方法分析了辊环装配的应力和应变，推导出辊环装配的整体条件，给出了装配工艺确定方法和计算公式，并将其应用于生产实际，获得了满意的结果。     

钢中白点特征及形成机理的研究

白点是钢中比较常见的低倍缺陷。白点作为钢中的显微裂纹,很可能成为疲劳裂纹源,降低钢的强度。为此,探讨了钢中白点的特征和形成机理,提出了消除白点的根本措施,以改进其机械性能,提高产品质量。     

合金结构钢锻后防白点处理的工艺实践

白点是钢中细小的內部裂纹。在钢的横向截面上白点呈现为细小弯曲的锯齿状裂纹,在纵向断口上呈现为园形或椭园形的银白色斑点。白点的危害性极大,它不仅使钢的机械性能,尤其是塑性急剧降低,使零件在热处理时容易产生开裂,而且由于白点产生高度的应力集中,使零件在承载时(尤其是在动载负荷下工作时)发生骤然破坏,造成严重的破坏事故。因此,在任何情况下都不允许使用有白点的锻件和用有白点的钢材加工制造机器零件。大部分合金结构钢(主要是含铬、镍、钼、钨、锰等元素的结构钢)和铬轴承钢,都有不同程度产生白点的敏感性,因此,防白点处理是合金结构钢,轴承钢锻造生产工艺中     

低合金钢中白点产生的原因分析

钢中白点是钢质的致命缺限，可导致钢材内部产生微裂纹，采用扫描电镜等分析手段探讨了钢中白点的形成过程，并通过对典型断口白点的微以形貌观察，分析热轧状态与调质状态白点的形态差异，提出预防白点的工艺措施。     

Thermal fracture endurance of cast irons with application study of pig iron ingot molds

Pig iron ingot molds manufactured with flake, compacted graphite cast iron, and spheroidal graphite cast iron were installed on a pig iron casting machine and subjected to thermal cycling for studying thermal fracture endurance of the three cast irons. The effects of graphite morphology on the fracture mechanism were analyzed by examining the fracture patterns, microstructures, and microcracks in the failed molds. The determining factors of thermal fracture endurance were elucidated with thermal fracture resistance indices. Compacted graphite cast iron exhibited better thermal fracture endurance than flake and spheroidal graphite cast irons because of its higher strength-to-thermal stress ratio.     

Vertebral artery injury associated with a Jefferson fracture

BACKGROUND: The evaluation and treatment of Jefferson fractures, a burst fracture of the ring of Cl, has been well documented in the medical literature. Vertebral artery injury associated with a Jefferson fracture is very rare. METHODS: The case study technique was used to summarize the case. Review of the literature was performed to discuss the case. Retrospective chart review of the 174 patients with cervical fractures admitted to St. Michael's Hospital from 1989-1994 was also performed. RESULTS: The case of a patient with a Jefferson fracture, with bilateral lateral displacement of the lateral masses causing bilateral vertebral artery occlusions resulting in a lateral medullary and cerebellar infarction is reported. A review of the literature is provided. CONCLUSION: A high index of suspicion for this injury is paramount, especially in patients with multiple trauma, where the diagnosis of Jefferson fractures can be delayed.     

Cranial burst fracture in infants: acute recognition and management

In the past, the diagnosis of "growing skull fracture" or "diastatic fracture" has included a subset of injuries better referred to as "cranial burst fracture." Cranial burst fracture, typically associated with severe injury in infants less than 1 year of age, is a closed, widely diastatic skull fracture accompanied by acute cerebral extrusion outside the calvarium. We treated 11 such infants at the LeBonheur Children's Medical Center and 2 at the Children's National Medical Center from January 1986 through December 1994. Infants ranged in age from 1 to 17 months, with an average age of 5.7 months. All presented with marked scalp swelling and a Glasgow Coma Scale score of 10 or less. Twelve had a history consistent with severe injury (motor vehicle accident, 7, abuse 5). The cause of injury in one patient remains unproven. Surgery (reduction of herniated cerebral tissue, repair of large dural laceration, and cranioplasty) was usually performed within 10 days of injury, a time period long enough to assure hemodynamic stability and resolution of acute cerebral swelling, yet sufficiently brief to avoid the chronic changes (scarring, parasitization of scalp vessels by damaged cortex) associated with a "growing skull fracture." Prompt repair of cranial burst fracture may prevent ongoing brain injury such as has been neuropathologically demonstrated in patients with "growing skull fracture." Magnetic resonance imaging establishes the diagnosis of cranial burst fracture in equivocal cases, rendering unnecessary a "waiting period" to see if scalp swelling resolves. Our experience, together with information in the neuropathological and neurosurgical literature, suggests that cranial burst fracture is associated with severe trauma, requires expeditious treatment, and has been underdiagnosed in the past, leading to "growing skull fracture," a condition requiring more extensive surgery.     

Structure and properties of a splat cooled 2024 aluminum alloy

Pound lots of splat cooled 2024 aluminum flake materials were produced by rapidly quenching the atomized melt against a rotating copper disc. Three flake sizes were selected, cold compacted into aluminum cans, and extruded at 300°C at a reduction ratio of 20 to 1. The extruded rods were reduced 50 pct by cold swaging, solution treated at 495°C, water quenched, and naturally aged. The splat cooled 2024 alloy had constituent particles of 1 fim and finer (compared to 5 to 20 μm for the commercial alloy); further, one of the complex constituent phases (AlCuFeMn) was essentially eliminated by the rapid quench. Compared to commercial 2024-T4, the splat cooled 2024 alloys showed 14 to 17 pct increase in yield and tensile strength (no loss of ductility) a seven-fold increase in fatigue life at 30,000 psi, and a large improvement in the 300°F (150°C) stress rupture life in tests beyond 100 h. The fracture characteristics of the splat alloys, while exhibiting excellent to superior ductility, appear inhomogeneous due to the presence of finely dispersed oxide films scattered in the structure. Formerly Research Assistant, Department of Metallurgy and Materials Science, Massachusetts Institute of Technology     

类金刚石薄膜在锥形纳米压头作用下的断裂分析

硬薄膜往往具有较脆的特性,在过载时易发生脆性断裂.本文研究了硬薄膜/软基体在锥形纳米压头作用下的断裂模式.利用等离子体化学沉积法在聚二醚酮基体上沉积生成类金刚石薄膜.使用纳米压痕法对其进行实验研究,实时记录纳米压头压入样品过程中所受的载荷以及位移.载荷位移曲线中有若干间断点,代表着裂纹的形成和扩展.压痕实验完成后,通过扫描电子显微镜和聚焦离子束观察发现,类金刚石薄膜压痕处出现规则的贯穿厚度的环形裂纹和径向裂纹.最后,利用有限元法分析了硬薄膜/软基体在锥形压头作用下的应力分布,通过cohesive单元模拟环形裂纹的起始和扩展.结果表明:环形裂纹是由薄膜表面较高的径向拉应力引起的,较高的径向拉应力发生于压头和薄膜表面接触区域的外侧;径向裂纹则是由薄膜在界面附近较大的拉应力引起的.并且,各圈环形裂纹的半径基本呈线性递增,这和实验观测基本相符.      

山东金青顶矿区深部矿体开采诱发微震活动分析

随着金青顶矿区开采深度的增加,地应力值逐渐增大,造成巷道围岩破坏越来越严重,且具有一定的岩爆倾向性。为进一步探究金青顶矿区深部开采诱发岩体破裂失稳规律,在金青顶矿区深部建立矿山微震监测系统,连续实时采集井下微震活动信息,对-825 m中段Ⅴ号矿体11#试验采场开采活动进行连续监测,重点分析开采扰动下岩体破裂前累计视体积、能量指数和施密特数等微震参数的变化特征,得出当前矿体整体损伤程度较小,岩体破裂主要是由岩体开挖以及爆破振动引起。     

TC11钛合金疲劳性能及其断口特征

研究了ＴＣ１１钛合金三种不同显微组织的旋转弯曲疲劳性能及其断口特征，探讨微观机理，从理论上解决了三种显微组织即等轴、混合及片状组织的旋转弯曲疲劳性能差异之所在，为ＴＣ１１找到了旋转弯曲疲劳性能较好的显微组织提供了依据。     

Thoracolumbar burst fracture. A biomechanical investigation of its multidirectional flexibility

Assessment of clinical instability of thoracolumbar burst fractures remains controversial and subjective. The purpose of the study was to obtain objective measures of acute instability of these fractures. Thirteen fresh cadaveric human spine specimens (T11-L1) were subjected to high-speed axial trauma, resulting in burst fractures in 10 specimens. Multidirectional flexibilities were measured when the specimen was intact and after the trauma. The average ranges of motion of the burst fractures, measured as percentages of the corresponding intact values at 7.5 Newton-meters, were 202%, 403%, 266%, and 462% for flexion/extension, axial rotation, lateral bending, and tension/compression, respectively. For the neutral zone motion parameter, the motions of the burst fracture were even greater: 670%, 1650%, 779%, and 650%, respectively. All of the increases were significant (P < 0.05). The clinical significance of the study lies in its finding of high multidirectional acute instability of the thoracolumbar burst fracture, especially in axial rotation.