Crack spacing threshold of double cracks propagation for large-module rack

Large-module rack of the Three Gorges shiplift is manufactured by casting and machining, which is unable to avoid slag inclusions and surface cracks. To ensure its safety in the future service, studying on crack propagation rule and the residual life estimation method of large-module rack is of great significance. The possible crack distribution forms of the rack in the Three Gorges shiplift were studied. By applying moving load on the model in FRANC3 D and ANSYS, quantitative analyses of interference effects on double cracks in both collinear and offset conditions were conducted. The variation rule of the stress intensity factor(SIF) influence factor, RK, of double collinear cracks changing with crack spacing ratio, RS, was researched. The horizontal and vertical crack spacing threshold of double cracks within the design life of the shiplift were obtained, which are 24 and 4 times as large as half of initial crack length, c0, respectively. The crack growth rates along the length and depth directions in the process of coalescence on double collinear cracks were also studied.

Non-parallel double-crack propagation in rock-like materials under uniaxial compression

Coalescence among fractures would have influence on the stability of rock masses. Deep understanding of mechanical behavior of fractured rock masses is an important mean to identify failure mechanism of geological disaster. In this study, crack propagation processing was studied through loading pre-fractured specimens of concrete block, termed as rock-like material, in uniaxial compression tests. New non-parallel double-crack geometry was introduced to observe crack coalescence. The flaw combinations are different from the normally used flaw configurations. In addition, ultrasonic detection tests were performed on the test blocks. The stress and strain data of these tests and characteristic parameters of sound wave were recorded. The stress-strain curves of each test block under the uniaxial compression test were drawn, relations among deformation characteristics and crack angle of the crack specimens, and their overall strength were analyzed. It is found that strength of the specimen decreases as crack inclination increases under two crack inclinations. The highest uniaxial compressive strength is found in the specimen with the cracks at the same angle in different directions. Based on description of the crack initiation location, crack surface and the ultimate failure patterns, failure modes of eight subtype for test blocks are divided into three categories. It is expected that the study results could be beneficial for engineering application of jointed rock masses.

Interface crack problems for mode Ⅱ of double dissimilar orthotropic composite materials

The fracture problems near the similar orthotropic composite materials are interface crack tip for mode Ⅱ of double disstudied. The mechanical models of interface crack for mode Ⅱ are given. By translating the governing equations into the generalized hi-harmonic equations, the stress functions containing two stress singularity exponents are derived with the help of a complex function method. Based on the boundary conditions, a system of non-homogeneous linear equations is found. Two real stress singularity exponents are determined be solving this system under appropriate conditions about bimaterial engineering parameters. According to the uniqueness theorem of limit, both the formulae of stress intensity factors and theoretical solutions of stress field near the interface crack tip are derived. When the two orthotropic materials are the same, the stress singularity exponents, stress intensity factors and stresses for mode II crack of the orthotropic single material are obtained.

Simulation of crack coalescence mechanism underneath single and double disc cutters by higher order displacement discontinuity method

The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics(LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical method.The main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double discs.The effects of specific disc parameters(except speed) on the thrust force Ft, the rolling force Fr, and the specific energy ES are investigated. It has been shown that the specific energy(energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth Pd(i.e. S/Pd ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.

Crack-tip field on mode Ⅱ interface crack of double dissimilar orthotropic composite materials

Two systems of non-homogeneous linear equations with 8 unknowns are obtained.This is done by introducing two stress functions containing 16 undetermined coefficients and two real stress singularity exponents with the help of boundary conditions.By solving the above systems of non-homogeneous linear equations,the two real stress singularity exponents can be determined when the double material parameters meet certain conditions.The expression of the stress function and all coefficients are obtained based on the uniqueness theorem of limit.By substituting these parameters into the corresponding mechanics equations,theoretical solutions to the stress intensity factor,the stress field and the displacement field near the crack tip of each material can be obtained when both discriminants of the characteristic equations are less than zero.Stress and displacement near the crack tip show mixed crack characteristics without stress oscillation and crack surface overlapping.As an example,when the two orthotropic materials are the same,the stress singularity exponent,the stress intensity factor,and expressions for the stress and the displacement fields of the orthotropic single materials can be derived.

Fracture evolution characteristics of sandstone containing double fissures and a single circular hole under uniaxial compression

The uniaxial compression experiments on the sandstone samples containing double fissures and a single circular hole were carried out by using electro-hydraulic servo universal testing machine to investigate the effect of rock bridge angle β and fissure angle α on mechanical properties and evolution characteristics of cracks.The results show that the peak strength,peak strain and elastic modulus of defected specimens decrease comparing with those for intact sample,and show a decreased trend firstly and then increase with β changing from 0° to 90°.The peak strength and elastic modulus achieve the minimum value as the rock bridge angle is 60°,while the peak strain reaches the minimum value with the rock bridge angle of 45°.The crack initiation of tested rock samples occurs firstly in stress concentration areas at tips of prefabricated fissures under uniaxial compression,and then propagates constantly and coalescences with the prefabricated hole.Some secondary cracks initiate and propagate as well until buckling failure happens.The rock bridge angle has a great influence on crack initiation,coalescence,final failure mode,crack initiation stress and transfixion stress.The peak strength varies significantly,while the elastic modulus and peak strain change slightly,and the failure modes are also different due to the influence of fissure angle.

Double plate system with a discontinuity in the elastic bonding layer

The double plate system with a discontinuity in the elastic bonding layer of Winker type is studied in this paper. When the discontinuity is small, it can be taken as an interface crack between the bi-materials or two bodies （plates or beams）. By comparison between the number of multifrequencies of analytical solutions of the double plate system free transversal vibrations for the case when the system is with and without disconti- nuity in elastic layer we obtain a theory for experimental vibration method for identification of the presence of an interface crack in the double plate system. The analytical analysis of free transversal vibrations of an elastically connected double plate systems with discontinuity in the elastic layer of Winkler type is presented. The analytical solutions of the coupled partial differential equations for dynamical free and forced vibration processes are obtained by using method of Bernoulli＇s particular integral and Lagrange＇s method of variation constants. It is shown that one mode vibration corresponds an infinite or finite multi-frequency regime for free and forced vibrations induced by initial conditions and one- frequency or corresponding number of multi-frequency regime depending on external excitations. It is shown for every shape of vibrations. The analytical solutions show that the discontinuity affects the appearance of multi-frequency regime of time function corresponding to one eigen amplitude function of one mode, and also that time functions of different vibration basic modes are coupled. From final expression we can separate the newgeneralized eigen amplitude functions with correspon- ding time eigen functions of one frequency and multifrequency regime of vibrations.

Inter-Toe Cracks: A Cosmetic Response versus Excipient. Efficacy and Tolerance Evaluation

A randomized, monocentric, double-blind, intra-individual excipient-controlled comparative study was performed to evaluate the efficacy and tolerance of an active peptide (laminin 5 fragment [LN-5]) formulated in cosmetic balm, versus excipient in inter-toe cracks. Two products were tested on 10 healthy volunteers. Each of them suffered from this particular superficial wound characterized by a peeling off a skin tab between at least two inter-toe spaces. The duration of this study belonged of 28 days with an intermediate visit to D14. Initial and outcome evaluation was performed using a 4-grade-scale depending on the severity of the inter-toe cracks. Tolerance and healing were assessed using macrophotographs. At D14 and D 28, the difference of cure between the 2 treatments was in favor of the peptide active product. The clinical score showed a best efficiency of the active compared with the excipient;indeed a significant difference between D28 and D0 was observed for the active ingredient. Active product repairs more quickly inter-toes cracks than the excipient and we noted the complete disappearance of the “severe” and “moderate” stages from the 14th day. This study showed clearly a fast (in 14 days) and beneficial effect of the application of LN-5 compared with the excipient, on the cutaneous repair of inter-toes cracks. Since LN-5 fragment is capable of producing immediate biological activity and reinforcing the dermal-epidermal junction, it can accelerate tissue repair.

基于复合图双卷积神经网络的路面裂缝识别方法

为了建立一种基于深度学习卷积神经网络的路面检测模型,提高特殊路面裂缝,如白裂缝、浅裂缝、潮湿裂缝、修补开裂等的识别准确率,在单卷积神经网络结构(单网络)上,提出了基于复合图双卷积神经网络的路面裂缝识别方法。首先,该方法在输入灰度图基础上,考虑裂缝病害图像特征,增加对应二值图组成复合图通道;其次,在单网络结构基础上增加一个针对特殊裂缝识别的单网络,非特殊裂缝网络训练使用全部数据,特殊裂缝网络训练使用特殊裂缝数据,两个网络参数分别独立更新,从而形成复合图双网络结构;然后两个网络分别对同一测试数据进行判定,得出各自的概率矩阵,最后再根据概率单侧抑制的原理将两个单网络输出结果进行叠加,得出最终识别结果。组织了70万张检测车采集图片对复合图双网络方法进行训练和测试。结果表明,复合图双网络识别重叠度、精确度、召回率显著优于灰度图单网络,证明了提出的两处优化,即将单通道灰度图改造为双通道复合输入图和增加一个特殊裂缝识别网络,提升了非特殊裂缝与特殊裂缝区域识别能力。此外,复合图双网络的重叠度、精确度、召回率指标比其他深度学习路面裂缝识别算法方法高。

无导洞法连拱隧道先行洞仰拱开裂及受力分析

研究目的:为探明无导洞法连拱隧道先行洞仰拱衬砌开裂的原因,本文首先通过现场监测得到先行洞的受力规律,然后基于该受力特征提出一种考虑后行洞开挖的先行洞荷载-结构计算模型,进而结合现场监测和数值计算分析先行洞仰拱衬砌的开裂原因,最后评价先行洞二衬的安全性并给出相应的控制措施。研究结论:(1)当后行洞开挖前,先行洞二衬对称受力且各截面的安全系数大于2.4;当后行洞开挖后,先行洞二衬处于偏压受力状态,仰拱右侧的安全系数仅为1.25,其内表面恰是最大拉应力所在位置,与现场仰拱衬砌的开裂位置吻合;(2)先行洞仰拱衬砌开裂的原因是由于后行洞开挖导致的隧道偏压受力以及仰拱不均匀沉降;(3)提高支护抗力系数有助于改善衬砌结构的安全性,但支护抗力系数高于某值后安全系数变化不大;(4)本研究成果可为相关连拱隧道的设计和施工提供参考。

含表面双裂纹的钻杆管体断裂性能研究

钻杆刺漏是钻杆在服役过程中最常见的失效形式,而钻杆表面裂纹的扩展是钻杆发生刺漏的直接原因。为更有效地评估钻杆表面含有多条裂纹时的安全性能,以某超深直井G105钻杆井口段为研究对象,建立管体外表面双裂纹有限元模型,分析了拉扭载荷下裂纹间距、次裂纹尺寸以及走向对环向主裂纹前缘J积分的影响。结果表明:轴向排列的环向次裂纹是相对最安全的,可大幅消减钻杆主裂纹前缘的J积分;环向排列的环向次裂纹相对最危险,可大幅增大钻杆主裂纹前缘的J积分;轴向次裂纹可增大钻杆主裂纹前缘或部分前缘的J积分,但增幅相对环向排列的环向次裂纹来说要微弱得多。次裂纹对主裂纹前缘J积分的影响强度随两裂纹间距的增大或次裂纹尺寸的减小而减小。因此在对含表面双裂纹的钻杆进行分析时,在次裂纹尺寸较大且距离较近的情况下应考虑次裂纹的影响;在次裂纹尺寸较小或距离较远时则可忽略次裂纹,将模型简化为单裂纹钻杆模型进行分析。

冻融雁行裂隙花岗岩单轴压缩宏细观疲劳特性试验研究

对于季冻区的岩体工程,岩石经常受到冻融和周期荷载扰动引起的耦合疲劳损伤。为了研究冻融裂隙花岗岩的疲劳开裂扩展情况,量化裂纹的损伤程度和分类类型,对冻融40次后的双裂隙花岗岩进行了3种应力振幅下的周期荷载试验。采用实时声发射和高速摄影监测技术来揭示裂纹演化,并进一步对不同的裂纹开裂类型进行分类,以帮助理解动态压裂规律,利用核磁共振测试分析裂隙花岗岩细观孔隙特征及其宏观力学特性的关系。结果表明:随着周期荷载振幅应力比的增加,双裂隙花岗岩在周期荷载“沉寂期”内的声发射计数增加;周期荷载阶段双裂隙花岗岩产生的剪切裂纹占比大于单调加载阶段,高振幅作用下岩石容易形成剪切破坏裂纹;双裂隙花岗岩声发射的最大幅值变小即大尺度破裂减少,周期荷载下岩样预制裂隙外尖端产生的向端面扩展裂纹的角度越大;双裂隙花岗岩的疲劳寿命减小,内部微裂隙扩展发育减缓,能够储存的含H流体也越少,最终表现为核磁共振T2谱面积变化率减小。

含平行双裂隙白砂岩力学行为数值分析

目的为探究平行双裂隙对白砂岩力学特性、裂纹扩展和能量演化的影响,方法利用颗粒流软件PFC2D获取白砂岩细观力学参数,通过改变双裂隙倾角和双裂隙间距2个关键影响因素,进行多次单轴压缩试验并对模拟结果进行分析。结果结果表明:随着裂隙倾角增大,岩石的峰值强度、弹性模量变大;随着平行双裂隙间距增大,裂隙倾角为30°时,岩石的峰值强度和弹性模量大幅降低,裂隙倾角为60°时,裂隙间距对岩石的峰值强度和弹性模量无显著影响,即裂隙间距转变为影响力学特性的次要因素;裂隙倾角对岩石的微裂纹发育过程有着重要影响,在裂纹扩展初期以拉伸裂纹为主,最终破坏形式多为剪切破坏;裂隙倾角为45°时,裂纹发育至贯通最为彻底;随着裂隙倾角增大,耗散能开始出现应变节点逐渐后移现象,岩石的弹性储能极限随之增强,裂隙倾角为0°~15°时,储能极限会发生一次小幅度反弹。结论双裂隙倾角和间距对白砂岩力学特性、裂纹扩展和能量演化的影响至关重要。

高铁隧道内地下水作用下双块式无砟轨道道床板裂缝扩展研究

针对我国高速铁路隧道内CRTSⅠ型双块式无砟轨道施工阶段道床板开裂问题,运用有限元软件建立隧道-无砟轨道三维实体模型,研究地下水作用下隧道内无砟轨道各结构层位移隆起变化规律,并结合FRANC3D软件,在道床板结构受力最不利位置插入不同形状的预制三维裂缝,分析水压、裂缝长度对道床板裂缝扩展的影响。研究结果表明:(1)三角形荷载作用相较于均布荷载作用时,道床板位移隆起量虽有所减小,但地下水压的反复作用始终会影响轨道结构的平顺性,甚至导致道床板与仰拱填充间出现离缝;(2)裂缝长度是裂缝失稳扩展的控制因素,在排水系统完全堵塞时,建议将裂缝长度控制在200 mm以内;(3)水压为裂缝扩展的关键影响因素,同等条件下水压越大,道床板裂缝扩展越迅速,均布荷载下道床板裂缝尖端应力强度因子是对应三角形荷载下的1.2~1.4倍。

采用DIC技术的超高性能混凝土的断裂性能研究

为研究超高性能混凝土(UHPC)的Ⅱ型断裂性能,对不同初始缝高比(a/W)的UHPC双缺口立方体(DNC)试件进行了抗压试验。基于数字图像相关(DIC)技术分析了UHPC的DNC试件的失效特征和裂缝扩展过程,得到了UHPC的Ⅱ型断裂参数,并评估了不同a/W下UHPC的断裂性能。试验表明:试件的破坏模式为沿缺口尖端发生局部偏剪切破坏,其主裂缝包括斜裂缝和左、右垂直裂缝,试件的荷载-位移曲线呈现出双峰值现象,两个峰值荷载分别对应斜裂缝和垂直裂缝充分扩展的时刻;斜裂缝和垂直裂缝的张开位移(COD)和滑移位移(CSD)与韧带高度近似呈线性关系;随着a/W的增大,起裂荷载减小,断裂韧度和断裂能先增大后减小,斜裂缝的长度和起始角减小,斜裂缝缺口尖端处的COD减小,CSD基本不变。

ZSM-35沸石的合成及其催化裂解庚烷制烯烃

利用烷烃催化裂解制备轻烯烃的研究已取得显著进展,而提高轻烯烃产率和选择性仍然存在挑战。文中采用水热合成方法以吡咯烷(PYR)和十六烷基三甲基溴化铵(CTAB)为双模板剂制备了具有层状薄片堆叠构成的球形ZSM-35-0.01CTAB分子筛。通过PYR和CTAB的相互作用,相对于母体ZSM-35催化剂,ZSM-35-0.01CTAB比表面积和孔体积分别由309 m^(2)/g和0.19 m^(3)/g升至340 m^(2)/g和0.24 m^(3)/g。在正庚烷催化裂解过程中,相比于ZSM-35的27.68%和ZSM-35-0.005CTAB的32.19%,有促进中间体的传质,将C_(2)^(=)~C_(4)^(=)产率提升至37.05%。新的合成策略为调节ZSM-35沸石的形貌和尺寸提供了有效途径,并在烷烃裂解过程中提供了新的理论指导。

考虑干缩裂隙动态变化的优势流入渗模型

为解决定量评估干缩裂隙优势流的难题,基于双孔隙域入渗理论,将开裂土体分为裂隙两侧基质域、裂隙底部基质域与裂隙域三部分,结合Green-Ampt入渗模型,提出了一种考虑干缩裂隙动态变化的优势流入渗模型,并基于该模型探讨了降雨强度、裂隙初始面积率及裂隙深度对土体两域积水时间、优势流入渗量及入渗深度的影响规律。结果表明:干缩裂隙产生的优势流入渗量占总降水量的73.4%~91.4%,入渗深度为裂隙深度的3.1~7.2倍;降雨强度增大将缩短土体基质域积水时间,增大优势流入渗深度;降雨过程中干缩裂隙面积率减小使优势流入渗量减小;裂隙初始面积率增大使两侧基质域入渗量减小,优势流入渗量增大但入渗深度减小;裂隙深度增大使裂隙域积水时间延后,优势流入渗深度增大;模型计算结果与干缩裂隙实际入渗规律相符,同时避免了为裂隙域赋水力学参数带来的误差与不便。

一维六方压电准晶中具有双对称分支裂纹的断裂问题

研究一维六方压电准晶体中具有两条对称分支裂纹的断裂问题,利用复变函数方法分析得出双对称分支裂纹的应力场、电位移场和能量释放率的解析形式,分析讨论双对称分支裂纹尖端场强度因子受分支裂纹偏折角和裂纹长度的影响。经过研究得出:当0 <λπ<π/2时,随着裂纹偏折角的增大,主支裂纹尖端的无量纲应力强度因子逐渐减小;随着主支裂纹长度的增加,主支裂纹尖端的无量纲应力强度因子增加;随着分支裂纹长度的增加,主支裂纹尖端的无量纲应力强度因子增加。

某双联机油滤清器构件断裂故障成因排查

针对某柴油机用双联机油滤清器壳体及盖板多次开裂、固定盖板用双头螺柱多次断裂等一系列故障,从结构设计、原材料性能、安装尺寸及安装形式等方面进行了全面排查。经过分析,确定了故障原因在于原有机油滤清器的可拆卸性设计存在不合理之处。在拆卸过程中,由于撬角受力不均匀,导致了螺柱的断裂,同时也造成了机油滤清器盖安装孔破裂以及机油滤清器壳体安装螺柱处开裂等一系列问题。为了解决这些故障,改进了盖板结构设计并提高了双头螺柱等级,从而优化了双联机油滤清器的可拆卸性,以确保柴油机可靠运行。

双层纸塑袋包装器械的灭菌质量研究

目的:探讨双层纸塑袋包装器械经高压蒸汽灭菌后的灭菌效果、阻菌效果及灭菌过程中湿包、密封线开裂的发生率。方法:选取2018年12月1日—12月31日180件需包装的手术器械作为研究材料,随机分为观察组和对照组,每组各90件。对照组器械行单层纸塑袋包装,观察组器械行双层纸塑袋包装,灭菌结束后比较两组器械包灭菌合格率,密封线开裂、湿包发生率,无破损保存时间,使用过程中的破损率,并调查相关科室医生对器械包装功能的满意度,采用SPSS20.0软件进行数据分析。结果:观察组与对照组的灭菌合格率均为100.00%,观察组器械包24周存储过程中的总破损率小于对照组,差异有统计学意义(χ^(2)=4.731,P<0.05);观察组器械投入使用过程中的破损率低于对照组,差异无统计学意义(χ^(2)=2.406,P>0.05);医生对观察组器械包装的满意度高于对照组,差异有统计学意义(χ^(2)=5.835,P<0.05)。结论:双层纸塑袋包装器械有较好的灭菌效果,灭菌时湿包和密封线开裂发生率较低,且无破损保存时间长于单层包装,重复灭菌率低、医生满意度高,较单层纸塑袋包装应用效果更佳。