Effects of axial static stress on stress wave propagation in rock considering porosity compaction and damage evolution

A wave equation of rock under axial static stress is established using the equivalent medium method by modifying the Kelvin-Voigt model.The analytical formulas of longitudinal velocity,space and time attenuation coefficients and response frequency are obtained by solving the equation using the harmonic method.A series of experiments on stress wave propagation through rock under different axial static stresses have been conducted.The proposed models of stress wave propagation are then verified by comparing experimental results with theoretical solutions.Based on the verified theoretical models,the influences of axial static stress on longitudinal velocity,space and time attenuation coefficients and response frequency are investigated by detailed parametric studies.The results show that the proposed theoretical models can be used to effectively investigate the effects of axial static stress on the stress wave propagation in rock.The axial static stress influences stress wave propagation characteristics of porous rock by varying the level of rock porosity and damage.Moreover,the initial porosity,initial elastic modulus of the rock voids and skeleton,viscous coefficient and vibration frequency have significant effects on the P-wave velocity,attenuation characteristics and response frequency of the stress wave in porous rock under axial static stress.

Rock damage and fracturing induced by high static stress and slightly dynamic disturbance with acoustic emission and digital image correlation techniques

A series of coupled static-dynamic loading tests is carried out in this study to understand the effect of slightly dynamic disturbance on the rocks under high static stress.The acoustic emission(AE)and digital image correlation(DIC)techniques are combined to quantitatively characterize the damage and fracturing behaviors of rocks.The effects of three influencing factors,i.e.initial static stress,disturbance amplitude,and disturbance frequency,on the damage and fracturing evolution are analyzed.The experimental results reveal the great differences in AE characteristics and fracturing behaviors of rocks under static loads and coupled static-dynamic loads.Both the Kaiser effect and Felicity effect are observed during the disturbance loading process.The crack initiation,stable and unstable propagation in the highly-stressed rocks can be triggered by cyclic disturbance loads,and more local tensile splitting cracks are found in the rocks subjected to coupled static-dynamic loads.The damage and fracturing evolution of rocks during cyclic disturbances can be divided into two stages,i.e.steady and accelerated stages,and the increase rate and proportion of each stage are greatly affected by these influencing factors.High initial static stress,low disturbance frequency,and high disturbance amplitude are considered to be adverse factors to the stability of the rocks,which would induce a high increase rate of the steady stage and a high proportion of the accelerated stage within the whole disturbance period.Based on the two-stage damage evolution trend,a linear-exponential damage model is employed to predict the instability of the rocks under coupled static-dynamic loads.

Piezoelectric responses of brittle rock mass containing quartz to static stress and exploding stress wave respectively

The electromagnetic emission(EME) induced from the rock containing piezoelectric materials was investigated under both static stress and exploding stress wave in the view of piezoelectric effect. The results show that the intensity of the EME induced from the rock under static stress increases with increasing stress level and loading rate; the relationship between the amplitude of the EME from the rock under different modes of stress wave and elastic parameters and propagation distance was presented. The intensity of the EME relates not only to the strength and elastic moduli of rock masses,but also to the initial damage of the rock. The intensity of EME induced by stress wave reaches the highest at the explosion-center and attenuates with the propagation distance. The intensity of EME increases with increasing the elastic modulus and decreases with increasing initial damage. The results are in good agreement with the experimental results.

Three dimensional finite element analysis of acetabulum loaded by static stress and its biomechanical significance

Objective:To explore the mechanical behavior of acetabulum loaded by static stress and provide the mechanical basis for clinical analysis and judgement on acetabular mechanical distribution and effect of static stress.Methods:By means of computer simulation, acetabular three dimensional model was input into three dimensional finite element analysis software ANSYS7.0. The acetabular mechanical behavior was calculated and the main stress value, stress distribution and acetabular unit displacement in the direction of main stress were analyzed when anterior wall of acetabulum and acetabular crest were loaded by 1 000 N static stress. Results:When acetabular anterior wall loaded by X direction and Z direction composition force, the stress passed along 4 directions: (1)from acetabular anterior wall to pubic symphysis along superior branch of pubis firstly, (2)from acetabular anterior wall to cacroiliac joint along pelvic ring,(3)in the acetabulum,(4)from the suffered point to ischium. When acetabular crest loaded by X direction and Y direction composition force, the stress transmitted to 4 directions: (1)from acetabular crest to ilium firstly, (2)from suffered point to cacroiliac joint along pelvic ring,(3) in the acetabulum ,(4)along the pubic branch,but no stress transmitted to the ischium branch.Conclusion:Analyzing the stress distribution of acetabulum and units displacement when static stress loaded can provide internal fixation point for acetabular fracture treatment and help understand the stress distribution of acetabulum.

Static Stretching Combined with Conscious Slower Breathing May Increase Parasympathetic Activity and Reduce Stress in Adult Women

Background: Women are thought to be more susceptible to stress than men in a stressful society, and reducing stress is crucial for women to maintain their health. Static stretching (SST) is applied in various fields to not only increase muscle flexibility but also reduce stress. Additionally, conscious slower breathing (CSB) predominates parasympathetic activity, causing a relaxing effect. These results indicate that combining SST and CSB may be more useful in reducing stress. However, to the best of our knowledge, the effect of this combination remains unclear. Objective: This study aimed to elucidate the effects of the combination of SST and CSB on autonomic activity and stress in adult women. Methods: Eleven healthy Japanese adult female participants performed SST with nonconscious natural breathing for 20 min. The same participants performed SST in combination with CSB (2 s inspiratory and 4 s expiratory) for 20 min on another day. Salivary cortisol and chromogranin A levels were measured before and after stretching as stress markers of the hypothalamic-pituitary-adrenal axis and sympathetic nervous system. The coefficient of variation of the R-R interval (CVR-R) and high-frequency component (HF), which reflect parasympathetic nerve activity, and heart rate and low-frequency component (LF)/HF ratio, which reflect sympathetic nerve activity, were measured before, during, and after stretching. Results: SST decreased cortisol levels but with no significant changes in chromogranin A, heart rate, CVR-R, HF, or LF/HF ratio. The combination of SST and CSB increased CVR-R and HF levels in addition to decreasing cortisol levels but with no significant changes in chromogranin A, heart rate, or LF/HF levels. Conclusion: These results indicate that the combination of SST and CSB may increase parasympathetic activity and reduce stress. However, future randomized controlled trials with larger sample sizes should support this conclusion.

Static Stress Triggering Effects Related with M_s8.0 Wenchuan Earthquake

In this article, firstly, we calculated and analyzed the patterns of Coulomb stress changes induced by a sequence of strong earthquakes that occurred in Songpan （松藩）, Sichuan （四川） Province in 1973 and 1976, and discovered that the Ms8.0 Wenchuan （汶川） earthquake of 2008 was epicentered in a relevant Coulomb stress triggering zone. This suggests that the Coulomb stress on the middle and southern segments of the Longmenshan （龙门山） fault zone increased after the Songpan sequence of strong earthquakes, and the stress increment might cause the 2008 Wenchuan earthquake having al- ready occurred somewhat ahead of time. Further, we calculated and analyzed Coulomb stress changes coinduced by both the Songpan sequence and the Ms8.0 Wenchuan mainshock. The result shows that the Ms6.4 Qingchuan （青川） earthquake of May 25, 2008 on the northeastern segment of the Longmenshan fault zone was triggered by the Wenchuan mainshock, and that the southwestern segment of the fault zone is also in the stress triggering zone. Besides, the Maoxian （茂县）-Wenchuan fault （i.e., the back-range fault of the Longmenshan fault zone）, which extends parallel to the seismogenic fault of the Wenchuan earthquake, is in a shadow zone of the Coulomb stress changes, and therefore, its potential hazard for producing a strong or large earthquake in the near future could be reduced relatively.

Static and Thermal Analysis of Aluminium (413,390,384 and 332) Piston Using Finite Element Method

The main objective of this research was to examine the suitability of aluminium alloy to design a piston of an internal combustion engine for improvement in weight and cost reduction. The piston was modelled using Autodesk Inventor 2017 software. The modelled piston was then imported into Ansys for further analysis. Static structural and thermal analysis were carried out on the pistons of the four different materials namely: Al 413 alloy, Al 384 alloy, Al 390 alloy and Al332 alloy to determine the total deformation, equivalent Von Mises stress, maximum shear stress, and the safety factor. The results of the study revealed that, aluminium 332 alloy piston deformed less compared to the deformations of aluminium 390 alloy piston, aluminium 384 alloy piston and aluminium 413 alloy piston. The induced Von Mises stresses in the pistons of the four different materials were found to be far lower than the yield strengths of all the materials. Hence, all the selected materials including the implementing material have equal properties to withstand the maximum gas load. All the selected materials were observed to have high thermal conductivity enough to be able to withstand the operating temperature in the engine cylinders.

Complete Coulomb stress changes induced by the Ms7.6 earthquake in Lancang-Gengma, Yunnan and triggering of aftershocks by dynamic and static stress

The spatiotemporal evolution patterns of complete Coulomb stress changes caused by 1988 Ms7.6 earthquake in Lancang-Gengma, Yunnan, are calculated and studied. And the triggering problems of Ms7.2 Gengma shock occurring 13 minutes after the main shock and of Ms5.0―6.9 aftershocks within 24 days after the main shock are discussed. The results show that the spatial distribution patterns of complete Coulomb stress changes of the Ms7.6 main shock are strongly asymmetric. The areas of positive dynamic and static Coulomb stress are both coincident well with the strong aftershocks' loca-tions. The Ms7.2 Gengma shock and most of strong aftershocks are subjected to the triggering effect of dynamic and static Coulomb stresses induced by the Ms7.6 Lancang earthquake.

Static Yield Stress of Cement-based Grouting Material under Different Rheological Modes

To quantitatively estimate the workability of cement-based grouting material,from the perspective of rheology,the result of the static yield stress evaluated using the rate-controlled and stress-controlled modes,respectively,was compared using the Rheowin rheometer.Also,the correlation of workability and solid concentration of slurry with static yield stress was studied.Results show that the static yield stress of cement-based grouting slurry relates to the established slurry structure,and is the shear stress corresponding to the transformation of elastics to plastics;In rate-controlled mode,the static yield stress of the slurry is related to the shear rate.The higher the shear rate,the greater the yield stress of the slurry.For the stress-controlled mode,the result is more accurate and suitable for testing static yield stress under different water-cement ratios.Since the water-cement ratio has a good correspondence with the static yield stress and the static yield stress has a good correspondence with the slump flow of the slurry,the static yield stress is the minimum stress to be overcome when the slurry begins to flow and it reflects the yield behavior and structural stability of the cement.

Residual Stress and Deformation Analysis of Static Bonding Multi-layer Pyrex7740 Glass and Aluminum

Residual stresses and deformation of static bonding multi-layer Pyrex7740 glass and aluminum have important effects on performances of bonding parts. The stress and strain finite element analysis of anodic bonding can optimize the structure and process design, reduce the workload of the experiments, shorten the production cycle, improve the bonding quality, and reduce the process costs. In this paper, residual stresses and deformation in the static bonding two-layer （glass/aluminum）, three-layer （glass/aluminum/ glass）,five-layer（glass/aluminum/glass/aluminum/glass）and seven-layer （glass/aluminum/glass/aluminum/glass/ aluminum/glass） samples have been analyzed using nonlinear finite element simulation software MARC. The simulation results show that the shear stress distribution and deformation distribution in different multi-layer glass and aluminum samples are similar. The stress distribution along thickness at different typical positions in all multi-layer samples has characteristics of pulse pattern, which has pulse peak at the position of transition layers and then decreases abruptly to the minimum value at the positions of glass and aluminum. The maximum shear stress is located in the outside surface area in the transition layer between the top unconstrained glass layer and aluminum layer. The displacement distribution along thickness in all multi-layer samples increases gradually fi＇om the constrained bottom glass layer to the top unconstrained glass layer with abrupt step increase in the aluminum layers, The maximum deformations occur in aluminum layers. It is found that the minimum deformation distortion and the minimum shear stress occur in the three-layer static bonding sample.

静态应力扰动对走滑断层阶区附近地震破裂传播影响的二维数值模拟

动态破裂在走滑断裂带上阶区附近的传播能力控制了地震破裂的可能规模,而非均匀应力场对动态破裂的传播有显著影响。在本研究中,我们通过整合动态破裂模型和静态应力扰动模型,构建了走滑断层上的非均匀应力场,对走滑断层阶区附近前次动态破裂所产生的静态应力扰动对后续破裂传播行为的影响进行了二维动态破裂模型研究。模拟结果表明,当考虑到走滑断层上的地震复发行为时,即使前序地震破裂传播被阶区所阻挡,其所产生的静态应力扰动也可显著提升下次地震跨该阶区传播的能力。另外,不同的初始均匀应力使得动态破裂能够跨大致相同宽度的阶区传播。较大的应力降或者较小的断层强度比(S)能够使得动态破裂在相对较宽的阶区上传播。因此,在研究走滑断裂带不同分段的级联破裂模式时,需要考虑前序地震所造成的静态应力扰动影响。

发泡聚乙烯最大加速度-静应力曲线快速获取方法研究

目的研究快速、准确预测最大加速度-静应力曲线的方法。方法首先利用落锤冲击试验机获取了5个不同高度下,5种不同厚度的发泡聚乙烯的最大加速度-静应力曲线。在此基础上,分析对比文中3种不同的改进拟合法与已有的动应力与动能量多项式拟合法的区别。结果研究发现,当不区分高度的情况下,以最大加速度因子为函数值,以跌落高度、衬垫厚度、静应力为变量进行拟合时,其代表预测精度R^(2)的平均为0.835,相比动应力与动能量多项式拟合法的0.2996要高。但曲线右侧的预测精度偏低。引入以静应力为变量的多项式作为修正因子后,R^(2)的平均值为0.934。预测精度有所提高,右侧的预测偏差减小,但仍存在。在区分高度的情况下,以带有修正因子的公式进行预测时,R^(2)的平均值为0.984,曲线向右侧预测偏差逐渐增大的现象明显改善。结论区分高度情况下,利用带修正因子的预测公式可以快速且较准确地预测最大加速度-静应力曲线,可以为冲击防护设计及相关软件的开发提供一定的帮助。

矿物掺合料对复合胶凝材料浆体静态屈服应力的影响

复合胶凝材料浆体的静态屈服应力可用于表征浆体内部微观结构建立的特性,且对新拌水泥基材料的施工与3D打印过程有很大影响。本文研究了矿物掺合料的种类和掺量对复合胶凝材料浆体静态屈服应力变化规律的影响。研究发现,矿物掺合料的细度增大使颗粒表面的水膜层厚度减小,导致浆体的静态屈服应力增大。复合胶凝材料浆体的静态屈服应力在加水搅拌后的一段时间内缓慢增加,浆体结构建立速率较小。在加水搅拌后大约1.5 h,复合胶凝材料浆体的静态屈服应力迅速增大,表明浆体内部结构的连接程度已接近不可破坏的程度,浆体开始凝结,向固体状态转变。

岩体弱化方法及其在深部高应力硬岩机械化开采中的应用

战略性矿产资源的安全保供是国家重大战略需求,向地球深部要矿产资源在未来相当长一段时间内具有不可替代的战略性。为了保障矿产资源需求,深部高应力硬岩的安全高效开采是深部采矿必须解决的重大问题。首先,本文阐述了深部高应力硬岩采矿的技术挑战及“变害为利”的采矿变革思路,提出了高应力硬岩弱化后再开展机械破岩以实现商业化开采的关键技术对策。然后,总结了“接触式”和“非接触式”岩体弱化方法的机理、具体特点与发展现状,并对比分析了两类岩体弱化方法在辅助高应力硬岩机械破岩领域的发展潜力。最后,展望了以深部高应力硬岩热剥落损伤弱化辅助机械破岩为代表的安全高效连续采矿技术,为深部战略性矿产资源安全保供与深地工程发展提供了有益指导。

扰动诱发高应力岩石动力响应及岩爆灾变机制

为揭示深部矿山岩爆发生机制,以硬质红砂岩为研究对象,利用岩石动静组合加载试验系统开展了无轴向静压及4个轴压条件下的不同入射能冲击试验,获得了纯动载及动静组合加载下岩样的力学行为与破坏特征。结果表明:试样最终形态分为完整、轴向劈裂、表面剥离、即时型粉碎和滞后型粉碎五类,其中,表面剥离和滞后型粉碎两类破坏模式表现出“岩爆”特征,即Ⅰ型应力−应变曲线、峰后释放能量、岩石自身静应变储能驱动碎片弹射、明显压剪破坏面;根据碎片弹射与动力加载的相对时间,进一步将表面剥离与滞后型粉碎破坏分别对应深地工程中的“即时型”和“滞后型”岩爆;动力扰动是岩爆的关键诱发因素,触发岩爆的临界扰动能随轴压比升高而逐渐降低。

新型CFRP索股锚固体系设计及试验研究

为改善CFRP索股锚固体系的锚固性能及CFRP索股受力不均问题,研制了锚具内壁面带凹槽的CFRP索股锚固体系,对其进行了试验测试,分析了锚固体系破坏模式、荷载-位移、锚固效率、CFRP索股应变变化规律,通过应力变异系数评估了锚具内壁面凹槽设置和预张拉对CFRP索股应力不均匀改善的效果。研究结果表明,锚具内壁面设置凹槽和对CFRP索股进行预张拉能够提高锚固体系的锚固效率,锚固效率可达99%以上;试验观察到CFRP索股存在受力不均现象,引起CFRP索股受力不均的原因主要与CFRP索股长度不一致和粘结介质的剪切变形相关;通过在锚具内壁面设置凹槽和对CFRP索股进行预张拉能够改善锚固体系CFRP索股的应力不均程度,锚具内壁面凹槽深度为2 mm、间距为5 mm,预紧力为10%名义极限荷载时,锚固体系在自由段中点和加载端处的平均应力变异系数分别降低了7.16%、3.86%。

周向约束对木材压缩吸能特性的影响

通过准静态压缩试验,考察轻木、泡桐、杉木、毛白杨4种木材在周向约束条件时,顺纹和横纹的压缩力学行为、破坏形态、吸能特性,并利用t检验分析其差异显著性。结果表明:①周向约束木材的顺纹压缩应力-应变曲线仍表现为“三阶段”特征,周向约束可抑制木材剪切扩展、大幅屈曲变形等非稳态破坏,曲线平台阶段应力基本与破坏强度持平。②泡桐、杉木、毛白杨顺纹压缩的吸能能力、平台阶段平稳性显著提高,其单位体积吸能值分别提高了15.51%、53.02%、48.15%,理想吸能率增大了35.93%、24.24%、86.00%。③周向约束木材的径向与弦向压缩力学行为、吸能特性相似,木材压头侧边纤维受试样中部拉伸和剪切作用发生竖向剥离,并沿压缩方向产生裂纹。④与无约束压缩相比,周向约束轻木、泡桐横纹压缩应力-应变曲线形状无明显变化,径向压缩单位体积吸能值分别提高了325.51%、182.60%,弦向压缩单位体积吸能值分别提高了430.57%、255.66%;杉木、毛白杨周向约束时横纹压缩应力-应变曲线变为无平台区的“两阶段”形式,理想吸能率均显著降低。

低水胶比水泥浆体静动态流变行为的经时变化

基于浆体流动度、静态屈服应力以及小振幅振荡模式下储能模量,研究不同水胶比以及减水剂用量对浆体静动态流变行为经时变化的影响机制,探讨低水胶比浆体的静动态流变行为。研究结果表明:通过调整减水剂用量获得的初始流动度相同但水胶比不同的浆体,流动性经时变化存在显著的差异。极低水胶比浆体的流动性经时损失更为显著;但高减水剂用量时,浆体的流动性经时损失较小。基于静态屈服应力和储能模量G′表征了浆体静态流变行为的发展,发现颗粒胶体作用力和水化产物的桥接作用共同决定了浆体微观结构强度发展。低水胶比浆体的静态屈服应力和储能模量随时间延长增长更加显著。增加减水剂用量,可增大颗粒间距,抑制早期水化,有利于延缓颗粒网络强度发展。影响静动态流变行为内在机制的不同导致了浆体的静动态性能经时变化存在显著差异,其中水化产物的桥接作用是关键因素。

爆破扰动高应力巷道围岩力学响应特征研究

为研究深井厚硬顶板采场巷道围岩在高静载和强动载耦合作用下的力学响应,基于相似模拟试验分析原岩应力、采动应力及爆破扰动三阶段的巷道围岩应力场与位移场,结合光纤环向应变场研究巷道围岩破坏特征,探索爆破扰动应力波在不同煤岩体中的传播规律及巷道动力响应机制。研究结果表明:巷道开挖后顶底板卸压明显,两帮产生应力集中区,采动应力阶段应力集中区范围增加50%,爆破后顶板围岩沿垮落角大范围卸压,应力沿巷道左肩窝逆时针逐渐增大;浅部巷道围岩呈现向自由面膨胀–变形,受巷道肩窝处剪切滑移错动影响,锚杆、锚索支护场产生相反的位移量,应力波扰动后,巷道左帮产生拉伸裂纹并与锚杆支护场连成宏观裂纹,裂纹发育高度大于锚杆支护场高度;巷道围岩顶底板呈现明显的张拉破坏特征,左右肩角呈现张拉及剪切复合破坏形式;应力波由小阻抗介质进入大阻抗介质的衰减速度最快,在同种介质中衰减速度次之,由大阻抗介质进入小阻抗介质中应力波峰值反而增大,应力波峰值强度衰减后仍大于巷道顶板极限抗拉强度,导致巷道围岩大变形失稳并产生一定程度的动力响应。基于应力波连续穿过层状岩体理论模型,结合动静载叠加理论,可优化爆破参数从而实现减冲抗冲主被动联合支护。

不同主横梁建模方式对弧门静动力学模拟结果影响

针对弧形闸门有限元分析中采用不同建模方式易造成数值模拟结果差异性的问题,以贵州乌江沙沱水电站大型露顶式弧形闸门为例,从计算原理角度探究了主梁翼缘采用节点耦合法、厚度叠加法两种建模方式对闸门静动力学计算结果(三维非线性静力学、模态分析和瞬态动力学)的影响。通过对比分析发现:采用厚度叠加的简化方式增加了构件的刚度,对闸门静力复核不利;两种建模方式对闸门干湿模态下的振型和自振频率影响较小;采用节点耦合法获取的支臂垂向振动程度较厚度叠加法结果略大,支臂与主横梁连接处敏感区域的动应力较厚度叠加法结果明显增大。两种建模方式对闸门整体结构属性影响有限,对支臂与主横梁连接处等敏感区域进行计算复核时应尽量采用节点耦合法,使计算结果更偏于安全。