THREE-DIMENSIONAL INTERACTIONS OF A HALF-PLANE CRACK IN A TRANSVERSELY ISOTROPIC PIEZOELECTRIC SPACE WITH RESULTANT SOURCES

Exact solutions in elementary functions are derived for the stress and electric displacement intensity factors of a half-plane crack in a transversely isotropic piezoelectric space interacting with various resultant sources, including force dipole, electric dipole, moment, force dilatation and rotation. Such force and charge sources may model defects like vacancies, foreign particles and dislocations. The locations and orientations of the stress and charge sources with respect to the crack are arbitrary.

THREE-DIMENSIONAL INTERACTIONS OF CIRCULAR CRACK IN TRANSVERSELY ISOTROPIC PIEZOELECTRIC SPACE WITH RESULTANT SOURCES

Exact solutions in form of elementary functions were derived for the stress and electric displacement intensity factors of a circular crack in a transversely isotropic piezoelectric space interacting with various stress and charge sources： force dipoles, electric dipoles, moments, force dilatation and rotation. The circular crack includes penny-shaped crack and external circular crack and the locations and orientations of these resultant sources with respect to the crack are arbitrary. Such stress and charge sources may model defects like vacancies, foreign particles, and dislocations. Numerical results are presented at last.

宽孔距爆破模型试验及近场动力学计算研究

针对宽孔距爆破破岩技术中炮孔密集系数合理取值的问题,在总结国内外宽孔距爆破破岩机理的基础上,开展了炮孔密集系数为1.7、2.5、3.5、4.5的有机玻璃板室内爆破试验,并基于常规态型近场动力学原理,开发了爆破计算模块,对宽孔距爆破破岩中裂纹扩展过程、介质位移响应规律进行了研究。结果表明:临空面一侧的径向裂纹受到临空面反射拉伸应力波的作用,表现出向临空面拐角分叉的特征,并逐渐向临空面扩展,最后形成主裂纹组成漏斗形状。在最小抵抗线固定不变条件下,随着炮孔密集系数的增加,应力降低区逐渐增大,同排炮孔间的径向贯通裂隙消失,过大的炮孔密集系数也进一步造成前后排孔间贯通裂纹消失,最后导致单孔爆破的情况发生。位移计算结果进一步证实了上述规律,并且当炮孔密集系数较小时,前排炮孔留下的岩埂刚好被后排炮孔爆破破碎,随着炮孔密集系数的增大,后排孔爆破对前排炮孔所留下的岩埂破碎作用效果逐渐降低。建议实际工程中根据岩体力学性质、地质条件以及爆破目的适当调整密集系数来降低炸药单耗与大块率。

炮孔间距对偏心不耦合装药贯通裂纹扩展的影响

为研究光面爆破中偏心不耦合装药炮孔间距对贯通裂纹扩展的影响,利用同心不耦合装药的孔壁压力计算公式并结合应力波叠加原理,推导偏心不耦合装药的炮孔间距计算方法。基于求得的炮孔间距范围,计算3种岩石介质在不同炮孔间距条件下贯通裂纹的扩展位置,并选择砂岩材料进行数值模拟。结果表明:偏心不耦合装药爆破中,贯通裂纹主要集中于偏心侧;抗拉强度大的岩石,贯通裂纹偏离炮孔连心线的程度也较大。砂岩的炮孔间距为60 cm时,贯通裂纹扩展方向与炮孔连心线重合,连心线下方出现裂纹比较集中的贯通区域;炮孔间距的增大导致贯通裂纹远离炮孔连心线,从而造成欠挖。偏心不耦合装药爆破后,偏心侧岩石的损伤明显大于非偏心侧。

双波导辐射对岩石裂纹扩展机理的影响

通过微波辐射能够使岩石迅速升温并产生扩展裂纹,从而大幅降低岩石强度,有助于解决全断面隧道掘进机(TBM)在破碎高强度硬岩地层时面临滚刀磨损严重、破岩效率低下、工程成本剧增等问题。为此,本文采用离散元软件PFC2D建立玄武岩的三相矿物(斜长石、橄榄石、辉石)模型,并进行双波导辐射模拟,探究波导间距(60、70、80、90及100 mm)、辐射时间(0、0.04、0.06、0.08及0.10 s)和围岩压力(5、10、15及20 MPa)对岩石损伤裂纹扩展的影响规律。结果表明:采用微波功率密度1×1010W/m3对玄武岩进行辐射加热时,为达到辅助破岩的效果,辐射时间不宜低于起裂时间(0.04 s)。微波辐射导致强吸波矿物(辉石)和弱吸波矿物(斜长石)间形成较大的温度梯度和热应力且最易产生损伤裂纹,所以裂纹产生的位置主要与岩石矿物的位置分布具有重要关系。在微波辐射岩石过程中,裂纹首先在辐射区域产生,继而在热膨胀和热应力作用下扩展延伸并在波导间的岩石区域形成裂纹贯通;随着波导间距的增加,波导间岩石裂纹贯通时所需要的微波辐射时间逐渐增加。围岩压力对裂纹的产生和扩展具有抑制和约束作用,其变化对岩样损伤裂纹的生成位置和扩展路径无明显影响,通过延长微波辐射的时间可以弥补因围压增加而减少的裂纹。

润宏煤业1305工作面静态膨胀剂致裂顶板卸压技术研究

以润宏煤业1305工作面地质条件为工程背景,采用静态膨胀技术对运输巷顶板切顶卸压,避免煤柱侧应力集中。通过理论分析、实验室测试、现场工程试验等方法,分析和测试了静态膨胀剂的膨胀力性能,计算分析了静态膨胀剂作用下切顶卸压的钻孔参数,设计了详细的施工工艺。研究结果表明,静态膨胀剂的最大膨胀力可达到70 MPa,且持续时间长,完全可以用于煤岩致裂工程。钻孔间距、钻孔直径以及钻孔角度是影响静态膨胀剂致裂效果的主要参数。钻孔内产生的静态膨胀压力作用到孔壁,且能一直保持到顶板进入采空区后,在矿压、自重及静态膨胀力的作用下,顶板会出现裂缝、裂缝扩展、顶板致裂垮落3个过程。根据现场具体工程条件,在多组成排钻孔共同膨胀作用下,可形成膨胀应力的叠加,能够起到更好的致裂效果。研究为探索和推广煤矿非爆破式顶板致裂技术提供了借鉴。

周边空孔与炮孔间距对爆破时围岩断裂损伤的影响

为探究周边空孔与炮孔间距对爆破时围岩裂纹扩展和损伤的影响机制,在理论分析炮孔间距对斜入射应力波反射以及卸载波对围岩应力分布影响的基础上,结合数值模型,分析有、无周边空孔和不同炮孔间距爆破时围岩断裂、损伤的变化。结果表明:空孔与炮孔间距是发挥空孔效应的关键因素。间距较小,炸药能量利用率降低,无法发挥空孔对裂纹扩展的导向作用,围岩爆破损伤严重;间距较大,空孔对应力波的反射作用减弱,空孔效应不足以使两孔之间的裂纹相互贯通,无法满足开挖要求;炮孔间距为800~1000 mm时的爆破效果最佳。空孔的增设可将爆破的炮孔间距扩大30%。

辽宁省高速公路沥青路面横向裂缝调查与分析

作为沥青路面主要病害形式之一,横向裂缝具有产生早、影响大、范围广等负面影响。为全面了解辽宁省高速公路沥青路面横向裂缝的分布情况,在辽宁省已通车高速公路中选取代表性较强的路段开展横向裂缝调查工作,并对横向裂缝的类型和形成原因进行分析。结合高速公路不同路面结构的调查结果,提出辽宁省高速公路沥青路面设计、施工及养护的具体建议。

钢-混凝土组合-叠合梁裂缝宽度计算方法研究

钢-混凝土组合-叠合梁是以提高负弯矩区组合梁的抗裂性为目的的一种新型结构。为研究该结构的裂缝开展和分布规律、裂缝宽度的计算方法,对2片钢-混凝土组合-叠合梁进行了负弯矩作用下的抗弯试验,探讨了裂缝的产生、发展和分布规律。通过与双面组合梁的裂缝发展规律对比验证了组合-叠合梁优越的抗裂性。基于试验结果讨论了组合-叠合梁裂缝的发展和分布规律;考虑钢与混凝土间叠合界面的初始粘结等作用,在开裂弯矩计算公式中引入界面系数,公式计算结果与试验结果吻合良好;最后,评估了《混凝土结构设计规范:GB50010—2010》和国内常用组合梁裂缝宽度计算公式对组合-叠合梁的适用性,经过修正得到了适用于组合-叠合梁裂缝宽度的计算公式,可为该类型结构的裂缝计算提供理论依据。

我国高校青年教师职业身份认同困境的空间解析与破解路径研究

青年教师作为高等教育深化改革发展的生力军和中坚力量,对自身职业身份的认同关乎其职业行为的选择与个体发展的向度。通过将列斐伏尔关于空间概念的三维分析,即空间范畴、空间演化历史以及空间生产与教师职业身份的关系解读,发现我国高校青年教师存在职业身份认同的空间困境,表现为空间范畴中的身份孤立与精神虚空、矛盾与差异空间中的身份偏差与疑惑、空间生产中的身份隐匿与变形。为摆脱困境,需注重“有机团结”的空间共同体构建,消解身份认同的孤独感;打造纪念碑空间,实现职业身份的诗意回归;推动空间解放,建构多元开放的教师职业形象。

川中高磨地区灯四气藏储层三维地质建模

四川盆地的碳酸盐岩广泛沉积,而GM井区的灯四气藏是主要的产能贡献区域,且地貌非常复杂,这些因素导致了该区域内储层的储集空间复杂,储层的非均质性很强,而且储层品质和发育位置之间存在很大的差异。为了更好地理解这些储层的差异,以便进行储层改造和优化开发政策,急需开展灯影组碳酸盐岩的三维地质建模研究。经过对构造建模、属性建模和天然裂缝建模方法的优化,建立了一个全面的三维地质模型。建模结果对不同井之间的储层预测具有高度可信度,并与研究区的实际地质情况相符。

射孔间距-倾角对深煤层水力裂缝扩展影响的离散元分析

研究煤岩储层裂缝扩展的影响因素,对提高煤层气采收率十分重要。为探究不同射孔间距-倾角对深层煤岩裂缝扩展规律的影响,利用离散元分析方法,考虑井周煤岩应力变化特征、最大周向应力准则、原始储层等条件,研究射孔间距-倾角对压裂缝网扩展形态及延伸范围的影响规律。模拟结果表明:随射孔间距从40 mm变化至100 mm,当间距为60 mm时裂缝条数数量最多;当射孔倾角从15°到60°变化时,当射孔角度为45°时,缝网形态最为复杂;即射孔间距为60 mm且射孔倾角为θ=45°时,水力裂缝的缝网形态复杂度显著增大,缝网扩展范围最大。通过神府北木瓜区Y-1井验证,预测结果与实测数据具有一致性,证明所建煤岩数值模型的正确性。

GH3230合金选区激光熔化成形工艺对激光焊开裂的影响研究

采用选区激光熔化技术(SelectiveLaserMelting,SLM)制备了GH3230镍基高温合金,研究了工艺参数对GH3230镍基高温合金激光焊接开裂的影响。实验表明,随着扫描间距从0.05mm增加至0.09mm的过程中,母材析出的碳化物平均尺寸在增大,母材晶粒尺寸明显减小,晶界角向右偏移,得到的晶界角分布变得更为均匀。在激光焊接后,由于遗传效应的影响,焊缝处的晶粒随着扫描间距的增大也同母材晶粒一起减小,晶界角分布变得更加均匀,提高整体抵抗裂纹能力,焊缝中裂纹总长和最大长度都逐渐降低,裂纹数量逐渐减少。最终得出在扫描间距为0.09mm时,成形的合金试样在多种焊接工艺条件下抵抗开裂的能力最佳。

基于YOLOv5的行李运输系统轮对裂纹检测算法

为了检测机场行李运输系统中轮对存在的裂纹,提出了一种基于YOLOv5的机场行李运输系统轮对裂纹检测方法。该方法针对裂纹细小、密集等特点采取了以下措施:在YOLOv5网络的Head部分使用SIoU替换了原有的CIoU;在Backbone部分加入了SE注意力机制;在Neck部分引入了Swin-Transformer模块;在整个YOLOv5网络中使用SPD-Conv替代了传统的Conv卷积模块;在图像的预处理方面,使用了图像分割与子图反向拼接技术。通过这些改进,有效地改善了YOLOv5对于细小、密集裂纹的特征提取能力,相较于传统的YOLOv5算法,裂纹检测的能力得到了有效提升。

边坡宽孔距大孔径预裂爆破技术研究及应用

针对某矿区溜井平台边坡预裂爆破工况,通过理论分析和结合现场实际情况,确定了合理的预裂爆破孔网参数范围、装药结构以及起爆延期时间等参数,并通过LS-DYNA数值模拟软件建立双炮孔预裂成缝模型并对边坡预裂爆破过程进行仿真分析。通过对多组模型成缝效果对比分析发现,确定孔径120 mm、孔距1.5 m进行预裂爆破综合效果最好,有利于边坡成形。现场爆破应用得出,预裂边坡壁面平整,半孔痕迹清晰,孔痕连续性完好,半孔率达75%左右,掌子面根部到达预裂线位置,爆破效果良好,无需二次处理,证实了宽孔距大孔径边坡预裂爆破技术在控制边坡成形方面效果良好,为类似工程提供了参考。

Crack elongation and its width of large depth reinforced concrete beams

In order to meet the requirement of structural inspection,the crack spacing and crack width at various heights in the tensile zone of six large depth reinforced concrete beams were measured under several loading levels of serviceability state.The effects of the depth of normal section beams on the crack spacing and crack width were analyzed,and the modified model is proposed for calculating the average crack spacing by thinking about the depth of normal section,the reinforcement arrangement and the effective reinforcement ratio.The relationships of crack widths at any position in the tensile zone and at the reinforcement level on the side surface of beam were studied.By theoretical and statistical analysis,a method is proposed to calculate the ratios of crack widths between any position and the reinforcement level on the side surface of large depth reinforced concrete beams.

RESEARCH ON THE FORMATION MECHANISM OF INTERNAL CRACK IN THE CONTINUOUS CASTING SLAB

In view of the periodic bending deformation of solid-liquid interface in the solidification process for continuous casting slab, the variation of temperature gradient and dendritic spacing in the front edge of the solid-liquid interface, and the nucleation and propagation process of crack were studied. It is shown that the bending deformation of the interface results in the temperature field change in the front edge of solid-liquid interface, and the occurrence of temperature gradient along drawing direction results in the growth of secondary dendrites. The initial crack formed during the middle and final stage of solidification may extend to the surface of the casting slab and become an internal crack. The results of the theoretical analysis are basically in agreement with that of the experiment.

THE CUT-AND-TRY METHOD IN DETERMINING THE SATURATE SPACING OF TRANSVERSE CRACKS OF COMPOSITE LAMINATES

In this Paper, the saturate spacing of transverse cracks of the 90° ply is originallycalculated by the 3-D finite element method. Thus, a new approach is put forward for predicting the saturate spacing of transverse cracks.

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.

ULF electric and magnetic anomalies accompanying the cracking of rock sample

The anomalies of electric-magnetic field and self-potential before earthquakes are important precursory phenom-ena. A simulating experiment study on the variations in ultra-low frequency (ULF) magnetic field and self-poten-tial during rock cracking was carried out in a magnetic field-free space. The results revealing in detail the whole process of the occurrences of electric and magnetic anomalies are significant for understanding the microscopic mechanism of ULF electric and magnetic signals. The experiment indicated that at the initial stage the slow changes in strain, self-potential and magnetic field with small amounts appeared firstly near the source of initial cracking, and then extended as the crack developed on. In the time domain, the self-potential anomaly emerged first and ULF magnetic field changes arose then. The shape of the ULF electric and magnetic anomaly varied ob-viously in early-, mid- and late-term of the test. The authors attributed the pulse-like changes of self-potential to the generation and movement of the accumulated electric charges during the cracking caused by charge separation on the crack tips within the sample. While the magnetic pulses of shorter-period at the last stage of the test, may be induced by instantaneous electric current of the accumulated charge during the cracking acceleration. The technical method and the observational results of this experiment are given in detail and the microscopic mechanism of elec-tric and magnetic precursors before earthquake are discussed in the present paper as well.