Mechanical properties and fracture surface roughness of thermally damaged granite under dynamic splitting

In order to understand the mechanical properties and the fracture surface roughness characteristics of thermally damaged granite under dynamic splitting,dynamic Brazilian splitting tests were conducted on granite samples after thermal treatment at 25,200,400,and 600℃.Results show that the dynamic peak splitting strength of thermally damaged granite samples increases with increasing strain rate,showing obvious strain‐rate sensitivity.With increasing temperature,thermally induced cracks in granite transform from intergranular cracks to intragranular cracks,and to a transgranular crack network.Thermally induced damages reduce the dynamic peak splitting strength and the maximum absorbed energy while increasing the peak radial strain.The fracture mode of the thermally damaged granite under dynamic loads is mode Ⅱ splitting failure.By using the axial roughness index Z2 a,the distribution ranges of the wedge‐shaped failure zones and the tensile failure zones in the fracture surfaces under dynamic Brazilian splitting can be effectively identified.The radial roughness index Z_(2)^(r)is sensitive to the strain rate and temperature.It shows a linear correlation with the peak splitting strength and the maximum absorbed energy and a linear negative correlation with the peak radial strain.Z_(2)^(r)can be used to quantitatively estimate the dynamic parameters based on the models proposed.

Stress-dependent shear wave splitting and permeability in fractured porous rock

It is well known that shear wave propagates slower across than parallel to a fracture, and as a result, a travelling shear wave splits into two directions when it encounters a fracture. Shear wave splitting and permeability of porous rock core samples having single fracture were experimentally investigated using a high-pressure triaxial cell, which can measure seismic shear wave velocities in two directions mutually perpendicular to the sample axis in addition to the longitudinal compressive wave velocity. A single fracture was created in the samples using a modified Brazilian split test device, where the cylindrical sample edges were loaded on two diametrically opposite lines by sharp guillotines along the sample length. Based on tilt tests and fracture surface profilometry, the method of artificially induced tensile fracture in the sample was found to create repeatable fracture surfaces and morphologies. Seismic velocities of the fractured samples were determined under different levels of stress confinement and fracture shear displacement or mismatch. The effective confining stress was varied from 0.5 MPa to55 MPa, while the fractures were mismatched by 0 mm, 0.45 mm and 1 mm. The degree of matching of the fracture surfaces in the core samples was evaluated using the joint matching coefficient(JMC). Shear wave splitting, as measured by the difference in the magnitudes of shear wave velocities parallel(V_(S1))and perpendicular(V_(S2)) to the fracture, is found to be insensitive to the degree of mismatching of the fracture joint surfaces at 2 MPa, and decreased and approached zero as the effective stress was increased.Simple models for the stress-and JMC-dependent shear wave splitting and fractured rock permeability were developed based on the experimental observations. The effects of the joint wall compressive strength(JCS), JMC and stress on the stress dependency of joint aperture were discussed in terms of hydro-mechanical response. Finally, a useful relationship between fractured rock permeability and shear wave splitting was found after normalization by using JMC.

Effect of dynamic loading orientation on fracture properties of surrounding rocks in twin tunnels

For expedited transportation,vehicular tunnels are often designed as two adjacent tunnels,which frequently experience dynamic stress waves from various orientations during blasting excavation.To analyze the impact of dynamic loading orientation on the stability of the twin-tunnel,a split Hopkinson pressure bar(SHPB)apparatus was used to conduct a dynamic test on the twin-tunnel specimens.The two tunnels were rotated around the specimen’s center to consider the effect of dynamic loading orientation.LS-DYNA software was used for numerical simulation to reveal the failure properties and stress wave propagation law of the twin-tunnel specimens.The findings indicate that,for a twin-tunnel exposed to a dynamic load from different orientations,the crack initiation position appears most often at the tunnel corner,tunnel spandrel,and tunnel floor.As the impact direction is created by a certain angle(30°,45°,60°,120°,135°,and 150°),the fractures are produced in the middle of the line between the left tunnel corner and the right tunnel spandrel.As the impact loading angle(a)is 90°,the tunnel sustains minimal damage,and only tensile fractures form in the surrounding rocks.The orientation of the impact load could change the stress distribution in the twin-tunnel,and major fractures are more likely to form in areas where the tensile stress is concentrated.

Application of split Hopkinson tension bar technique to the study of dynamic fracture properties of materials

A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.

Regulation of Pore Structure and Hightemperature Fracture Behavior of CACbonded Alumina-Spinel Castables Based on Hydration Design

The lamellar hydrates of CAC were designed with the introduction of nano CaCO_(3)or Mg-Al hydrotalcite(M-A-H),and the effects on the green strength,pore structures,and high-temperature fracture behavior of alumina-spinel castables were investigated.The results show that nano CaCO_(3)or M-A-H stimulates rapidly the hydration of CAC and the formation of lamellar C_(4)AcH_(11)or coexistence of C_(2)AH_(8)and C_(4)AcH_(11)at 25℃.The formation of lamellar hydrates can contribute to a more complicated pore structure,especially in the range of 400-2000 nm.Meanwhile,the incorporation of well-distributed CaO or MgO sources from nano CaCO_(3)or M-A-H also regulates the distribution of CA_(6)and spinel(pre-formed and in-situ).Consequently,the optimized microstructure and complicated pore structure can induce the deflection and bridging of cracks,thus facilitating the consumption of fracture energy and enhancing the resistance to thermal stress damage.

On the Orientation of Fractures with Transpressional and Transtensional Wrenches in Pre-Existing Faults

The orientation of fractures with transpressional and transtensional wrenches in pre-existing faults has not been quantitatively determined. Based on Coulomb failure criterion and Byerlee’s frictional sliding criterion, this paper has indicated quantitative geometric relationships between the pre-existing fault and the local induced principal stress axes caused by the rejuvenation of the pre-existing fault. For a hidden pre-existing fault with some cohesion, the angles between the local induced principal stress axes and the pre-existing fault quantitatively vary with the applied stress and the cohesion coefficient, the ratio of the thickness of the cover layer to the thickness of the whole wrench body, whether transpressional or transtensional wrenches occur. For a surface pre-existing fault with zero cohesion, the angles between the pre-existing fault and the local induced principal stress axes are related to the rock inner frictional angle regardless of both the applied stress and the cohesion coefficient where transpressional wrenches occur, and the local induced maximum principal stress axis is identical with the applied maximum principal stress axis where transtensional wrenches occur. Therefore, the geometric relationships between the pre-existing faults and their related fractures are defined, because the local induced principal stress axes determine the directions of the related fractures. The results can be applied to pre-existing weak fabrics. They can help to understand and analyze wrench structures in outcrops or subsurface areas. They are of significance in petroleum exploration.

A retrospective study of unfavorable fractures during sagittal split osteotomy:A single surgeon’s experience

Background:Unfavorable fractures are among the most common complications of bilateral sagittal split ramus osteotomy(BSSRO).This study aimed to evaluate unfavorable fracture patterns during BSSRO and assess the related risk factors and treatment measures.Methods:The clinical records and radiographs of 679 patients(1358 sides)who underwent BSSRO at Shanghai Ninth People’s Hospital between September 2013 and December 2021 were examined.Results:Patients with unfavorable fractures who underwent surgical restoration were studied.The incidence of unfavorable fractures was 0.8%(n¼11),with the highest rate in the third year.The unfavorable fractures were divided into three types by location and clinical treatment:(1)SSRO could still be completed after buccal/lingual plate unfavorable fracture(0.6%,n=8);(2)condylar/coronoid process fractures/intermaxillary fixation needed(0.1%,n=2);(3)additional osteotomy required(0.07%,n=1).Conclusion:These results suggest that as a surgeon’s experience increases,the rate of unfavorable fractures may decrease.The novel classification of unfavorable fractures for SSRO might be useful for surgeons to make appropriate treatment choices during orthognathic surgery.

Clinical Research of Pre-Hospital Emergency Care, Nursing, Infection Prevention and Control for Senile Osteoporotic Vertebral Compression Fracture during Epidemic Period

Background: Novel coronavirus pneumonia (NCP) and osteoporotic vertebral compression fractures (OVCF) are the high incidences of diseases in the elderly. During the epidemic period, if not treated in time, the complications are high and the mortality is high. If we do not pay attention to infection prevention and control in pre-hospital emergency care, it will lead to the first time infection of medical staff and in-hospital cross infection in emergency outpatient receiving area. The correct consideration of both and the establishment of perfect pre-hospital emergency treatment and infection prevention and control synchronous strategy is an important premise to ensure the stable, orderly and safe medical treatment. Objective: To explore the effect of synchronous implementation of pre-hospital emergency care, nursing and infection pre-vention and control for senile OVCF during the epidemic. In order to improve the efficiency of pre-hospital emergency care and prevent the spread of infection. Method: A total of 92 elderly patients with OVCF who received pre-hospital treatment in 18 hospitals in Zhangjiakou City during the epidemic prevention and control period from January 2020 to November 2022 and met the inclusion criteria were selected as research objects, including 24 males and 68 females, aged 65 - 82 (74.2 ± 2.2) years. All patients were associated with concomitant injuries and underlying diseases. All patients in this group underwent predictive pre-hospital rescue and infection prevention and control procedures. Results: All the 92 elderly patients with OVCF received timely pre-hospital treatment during the epidemic period, and no aggravation occurred of the 92 patients, 35 were in the high risk area, 10 were in the medium risk area, and 47 were in the low risk area. Exclude OVCF for NCP Patients were treated according to the conventional diagnosis and treatment principles. Suspected and confirmed cases are transferred to designated surgical hospitals for treatment. All patients were followed up 3 months, 6 months and 12 months after treatment. There was no death rate, high satisfaction of pre-hospital first aid, high diagnostic accuracy, and good curative effect. None of the rescue personnel had any infection rate, and no hospital infection transmission and nosocomial cross infection occurred. Conclusion: It is the first step to safely treat patients and prevent cross infection to establish a perfect synchronous strategy of pre-hospital first aid and infection prevention and control.

Dynamic notched semi-circle bend(NSCB) method for measuring fracture properties of rocks:Fundamentals and applications

Rocks are increasingly used in extreme environments characterised by high loading rates and high confining pressures.Thus the fracture properties of rocks under dynamic loading and confinements are critical in various rock mechanics and rock engineering problems.Due to the transient nature of dynamic loading,the dynamic fracture tests of rocks are much more challenging than their static counterparts.Understanding the dynamic fracture behaviour of geomaterials relies significantly on suitable and reliable dynamic fracture testing methods.One of such methods is the notched semi-circle bend(NSCB)test combined with the advanced split Hopkinson pressure bar(SHPB)system,which has been recommended by the International Society for Rock Mechanics and Rock Engineering(ISRM)as the standard method for the determination of dynamic fracture toughness.The dynamic NSCB-SHPB method can provide detailed insights into dynamic fracture properties including initiation fracture toughness,fracture energy,propagation fracture toughness and fracture velocity.This review aims to fully describe the detailed principles and state-of-the-art applications of dynamic NSCB-SHPB techniques.The history and principles of dynamic NSCB-SHPB tests for rocks are outlined,and then the applications of dynamic NSCB-SHPB method(including the measurements of initiation and propagation fracture toughnesses and the limiting fracture velocity,the size effect and the digital image correlation(DIC)experiments)are discussed.Further,other applications of dynamic NSCB-SHPB techniques(i.e.the thermal,moisture and anisotropy effects on the dynamic fracture properties of geomaterials,and dynamic fracture toughness of geomaterials under pre-loading and hydrostatic pressures)are presented.

Fracture and Tensile Properties of Polyvinyl Alcohol Fiber Reinforced Cementitous Composites

Experiments were carried out to design polyvinyl alcohol （PVA） fiber reinforced cementitous composites （PVA-FRCCs） holding high ductility and energy consumption ability. Besides, the properties of each ingredients in composites, mixing method and technology for fresh mixture were described in detail. Then, the pseudo-strain-hardening （PSH） behavior was investigated in uniaxial tension test. As a result, the maximum ultimate tensile strain can reach 0.7 percent. On the other hand, the single edge notch （SEN） thin sheet specimens were employed to gain the normal tensile load via crack mouth opening displacement （CMOD） curves, which can show obvious PSH behavior. In addition, the curves can be divided into four zones whose fracture toughness calculation methods were discussed. The wedge splitting （WS） test method can be applied to discuss the fracture toughness. Moreover, fracture energy of SEN and WS specimens were both approximately evaluated.

Dolomite fracture modeling using the Johnson-Holmquist concrete material model:Parameter determination and validation

In this paper,the Johnson-Holmquist concrete(JHC)constitutive model is adopted for modeling and simulating the fracture of dolomite.A detailed step-by-step procedure for determining all required parameters,based on a series of experiments under quasi-static and dynamic regimes,is proposed.Strain rate coefficients,failure surfaces,equations of state and damage/failure constants are acquired based on the experimental data and finite element analyses.The JHC model with the obtained parameters for dolomite is subsequently validated using quasi-static uniaxial and triaxial compression tests as well as dynamic split Hopkinson pressure bar(SHPB)tests.The influence of mesh size is also analyzed.It shows that the simulated fracture behavior and waveform data are in good agreement with the experimental data for all tests under both quasi-static and dynamic loading conditions.Future studies will implement the validated JHC model in small-and large-scale blasting simulations.

Determination of dynamic modeⅠfracture toughness of rock at ambient high temperatures using notched semi-circular bend method

To investigate the influence of loading rate and high temperature on the dynamic fracture toughness of rock,dynamic fracture tests were carried out on notched semi-circular bend specimens under four temperature conditions based on the split Hopkinson pressure bar system.Experimental and analytical methods were applied to investigating the effect of temperature gradient on the stress waves.A high-speed camera was used to check the fracture characteristics of the specimens.The results demonstrate that the temperature gradient on the bars will not significantly distort the shape of the stress wave.The dynamic force balance is achieved even when the specimens are at a temperature of 400°C.The dynamic fracture toughness linearly develops with the increase of loading rate within the temperature range of 25-400°C,and high temperature has a strengthening effect on the dynamic fracture toughness.

Statistical analysis of fracture properties based on particle swarm optimization and Pearson correlation coefficient method

Prediction of reservoir fracture is the key to explore fracture-type reservoir. When a shear-wave propagates in anisotropic media containing fracture,it splits into two polarized shear waves: fast shear wave and slow shear wave. The polarization and time delay of the fast and slow shear wave can be used to predict the azimuth and density of fracture. The current identification method of fracture azimuth and fracture density is cross-correlation method. It is assumed that fast and slow shear waves were symmetrical wavelets after completely separating,and use the most similar characteristics of wavelets to identify fracture azimuth and density,but in the experiment the identification is poor in accuracy. Pearson correlation coefficient method is one of the methods for separating the fast wave and slow wave. This method is faster in calculating speed and better in noise immunity and resolution compared with the traditional cross-correlation method. Pearson correlation coefficient method is a non-linear problem,particle swarm optimization( PSO) is a good nonlinear global optimization method which converges fast and is easy to implement. In this study,PSO is combined with the Pearson correlation coefficient method to achieve identifying fracture property and improve the computational efficiency.

A review of the New Geophysics:a new understanding of pre-fracturing deformation in the crack-critical crust with implications for hydrocarbon production

This paper reviews a new understanding of shear-wave splitting （seismic-birefringence） that is a fundamental revision of conventional fluid-rock deformation. It is a New Geophysics with implications for almost all solid-earth geosciences, including hydrocarbon exploration and production, and earthquake forecasting. Widespread observations of shear-wave splitting show that deformation in in situ rocks is controlled by stress-aligned fluid-saturated grain-boundary cracks and preferentially orientated pores and pore-throats pervasive in almost all igneous, metamorphic, and sedimentary rocks in the Earth＇s crust. These fluid-saturated microcracks are the most compliant elements of the rock-mass and control rock deformation. The degree of splitting shows that the microcracks in almost all rocks are so closely spaced that they verge on fracture-criticality and failure by fracturing, and are critical systems with the “butterfly wing＇s” sensitivity of all critical systems. As a result of this crack-criticality, evolution of fluid-saturated stress-aligned microcracked rock under changing conditions can be modelled with anisotropic poroelasticity （APE）. Consequently, low-level deformation can be： monitored with shear-wave splitting; future behaviour calculated with APE; future behaviour predicted with APE, if the change in conditions can be quantified; and in principle, future behaviour controlled by feed-back. This paper reviews our current understanding of the New Geophysics of low-level pre-fracturing deformation.

Fractographic and Fracture Mechanical Investigations of Refractories under Different Loading Conditions

Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories.A wedge splitting test procedure and a modified shear test have been applied.Test results have been used for material characterization especially with respect to brittleness.Furthermore a microscopic fractographic test procedure was developed and applied on fractured test specimens.In order to explain brittleness dependence on structure properties correlation of fractographic and fracture mechanical results has been evaluated.Frequently brittleness reduction is achieved by a lower amount of transgranular crack propagation associated with a strength decrease while maintaining specific fracture energy unchanged.Deviations from pure linear fracture mechanics increase with decreasing brittleness and contribute to specific fracture energy.Shear specimens may show two generations of cracks,a first one initiated by tensile loads （stable propagation） and a second one by shear loads （unstable propagation）.

Experimental study on tensile failure process of double-K fracture parameters in roller compacted concrete layer

Study on failure of soft stratum of roller compacted concrete (RCC) is an important aspect of stability of high RCC dam. Six kinds of specimens with different interfaces were investigated by wedge splitting method. Double-K fracture parameters (initial fracture parameter and unsteady fracture parameter) were calculated by the concrete double-K fracture theory. It is indicated that the approach of construction joint or old joint after RCC final set is the most efficient among the six cases, and its fracture parameter is the largest among them. Its propagation path is sinuous. Its failure surface is scraggly. Bedding plane crack fails at the underside of the concrete surface, bond course or the surface between them for each approach. So disturbance on the underside of the concrete surface should be avoided or decreased at best during RCC construction.

Relation between Loading Rate and Fracture Velocity on Limestone

The relation between loading rate and fracture velocity is the key to determining the fracture toughness of rock mass under dynamic loading.While designing an optimal blast design for any limestone mines,understanding the relationship between blast detonation pressure and rock fragmentation can increase the energy utilisation in any limestone mine blast.The detonation pressure is directly related to dynamic loading rate and fracture velocity is directly related to stress wave propagation speed during blasting.This paper discusses the relationship between dynamic loading rate and fracture velocity for limestone samples.It was observed that crack propagation velocity increases with fracture toughness of rock samples.It may be concluded that as the dynamic loading increases,the fracture velocity increases.

Effect of Reelin signaling on pre-plate splitting during cerebral cortex development

The development of the 6-layered cerebral neocortex is one of the most important events during nervous system development, and disturbances could result in various malformations, causing clinically intractable diseases, such as epilepsy and cerebral palsy. Pre-plate splitting is the first developmental step of the cortical plate formation. Without correct pre-plate splitting, normal cerebral cortex structures are disturbed. The Reelin-Dabl molecular pathway plays a critical role during cerebral cortex development, and deficiencies in this pathway result in failed pre-plate splitting and an inverted cortical plate. This paper summarizes findings involving Reelin and pre-plate splitting and further explores the precise role of Reelin during pre-plate splitting.

基于RHT本构模型的连续装药预裂爆破孔距优化研究

为解决北衙金矿在使用预裂爆破技术时整体爆破效果不佳的问题,基于RHT损伤本构模型,利用ANSYS/LS-DYNA数值模拟软件,开展了不同孔距下预裂爆破的数值模拟研究。结果表明:当预裂孔炮孔间距为120 cm时,孔间裂纹存在较为明显的分叉,且裂纹扩展范围较大;当炮孔间距为130 cm时,裂纹向四周扩展的范围减小,且炮孔周围岩石的损伤程度明显降低;当炮孔间距增加至140 cm时,相邻预裂孔连线上的裂纹仅在局部连通,无法实现孔间贯穿。上述结果说明,130 cm的炮孔间距在降低预裂爆破自身对岩体的扰动与实现有效爆破成缝之间达到了平衡。基于数值模拟试验结果开展了现场试验,爆破效果良好。研究结果可为矿山的预裂爆破设计和施工提供参考。

基于衰减各向异性理论的叠前裂缝预测技术及应用

天然裂缝对致密气和页岩气气藏的富集和高效开发有重要的支撑作用,地震裂缝预测则是部署钻井前的关键环节之一。然而,受地表复杂的采集条件、多变的处理流程和目的层岩性突变等因素影响,地震波在振幅和速度上可能表现出“伪方位各向异性”,导致传统的OVT域叠前各向异性裂缝预测的精度下降。在传统方位各向异性理论的基础上,从储层和裂缝对地震波的衰减出发,基于等效介质理论推导了衰减各向异性反射系数近似公式和方位衰减弹性阻抗(QVAZ)方程;结合贝叶斯和组稀疏反演方法建立目标函数,经过求解弹性矩阵获得相应流体项和裂缝弱度等参数,并实现三维裂缝密度高精度预测。利用单井数据进行试算,明确了衰减各向异性对裂缝的敏感性;结合实际钻井和OVT宽方位地震数据,反演分方位衰减弹性阻抗得到裂缝密度等关键参数,这些参数与钻井FMI成像测井解释的结果吻合度较高,证实了方法的可靠性,一定程度上避免了“伪方位各向异性”的现象。