A Numerical Study of Wave Propagation and Cracking Processes in Rock-Like Material under Seismic Loading Based on the Bonded-Particle Model Approach

An earthquake is usually followed by a considerable number of aftershocks that play a significant role in earthquake-induced landslides,During the aftershock,the cracking process in rocks becomes more complex because of the formation of faults.In order to investigate the effects of seismic loading on the cracking processes in a specimen containing a single flaw,a numerical approach based on the bonded-particle model(BPM)was adopted to study the seismic loading applied in two orthogonal directions.The results reveal that no transmission and reflection phenomena were observable in the small specimens(76 mm×152 mm)because they were considerably smaller than the wavelength of the P-wave.Furthermore,under seismic loading,the induced crack was solely tensile in nature.Repeated axial seismic loading did not induce crack propagation after the first axial seismic loading.Cracks began to propagate only when the seismic loading direction was changed from axial to lateral,and then back to axial,ultimately resulting in the failure of the specimen.

Behavior of Transversal Crack on Slab Corner During V-H Rolling Process

The behavior of transversal cracks on the surface of the slab corner during vertical and horizontal （V-H） rolling process with flat vertical roll and groove vertical roll was simulated by explicit dynamic finite element method. The closure and growth of crack and the contact pressure on surfaces of the crack in contacting zone between slab and roll during rolling process were analyzed. The results showed that during vertical rolling process, when the groove vertical roll is used, the maximum contact pressure on surfaces of the crack is 115 MPa, and the closure of crack is stable when the flat vertical roll is used, the maximum contact pressure on surfaces of the crack is 70 MPa, and it fluctuates greatly. During horizontal rolling process, when groove vertical roll is used, the contact pressure becomes zero which may accelerate the growth of crack when flat vertical roll is used, there is still contact pressure. The cal culated results are in good agreement with the results of test.

Dual-radiation-chamber coordinated overall energy efficiency scheduling solution for ethylene cracking process regarding multi-parameter setting and multi-flow allocation

Ethylene cracking process is the core production process in ethylene industry,and is paid more attention to reduce high energy consumption.Because of the interdependent relationships between multi-flow allocation and multi-parameter setting in cracking process,it is difficult to find the overall energy efficiency scheduling for the purpose of saving energy.The traditional scheduling solutions with optimal economic benefit are not applicable for energy efficiency scheduling issue due to the neglecting of recycle and lost energy,as well as critical operation parameters as coil outlet pressure(COP)and dilution ratio.In addition,the scheduling solutions mostly regard each cracking furnace as an elementary unit,regardless of the coordinated operation of internal dual radiation chambers(DRC).Therefore,to improve energy utilization and production operation,a novel energy efficiency scheduling solution for ethylene cracking process is proposed in this paper.Specifically,steam heat recycle and exhaust heat loss are considered in cracking process based on 6 types of extreme learning machine(ELM)based cracking models incorporating DRC operation and three operation parameters as coil outlet temperature(COT),COP,and dilution ratio according to semi-mechanism analysis.Then to provide long-term decision-making basis for energy efficiency scheduling,overall energy efficiency indexes,including overall output per unit net energy input(OONE),output-input ratio per unit net energy input(ORNE),exhaust gas heat loss ratio(EGHL),are designed based on input-output analysis in terms of material and energy flows.Finally,a multiobjective evolutionary algorithm based on decomposition(MOEA/D)is employed to solve the formulated multi-objective mixed-integer nonlinear programming(MOMINLP)model.The validities of the proposed scheduling solution are illustrated through a case study.The scheduling results demonstrate that an optimal balance between multi-flow allocation,multi-parameter setting,and DRC coordinated operation is reached,which achieves 3.37%and 2.63%decreases in net energy input for same product output and conversion ratio,as well as the 1.56%decrease in energy loss ratio.

Effect of gradient temperature rolling process on promoting crack healing in Q500 heavy plates

To ensure the quality of heavy plate products as determined by ultrasonic inspection, it is necessary to effectively control defects such as cracks and shrinkage cavities in heavy plates. Generally, some defects such as large size cracks exist due to insufficient deformation in the center of traditionally rolled plates. Compared with the traditional rolling process, gradient temperature rolling(GTR) process can effectively increase deformation inside heavy plates. In this study, the effect of GTR on crack healing was analyzed through a comparison experiment with the uniform temperature rolling(UTR). The results show that the GTR process could increase the plastic strain inside the heavy plate and effectively promote the healing process of the preset cracks. The degrees of crack healing at the center and quarter thickness position of the steel plate via GTR were greater than twice those of the plate via UTR. The GTR process can significantly reduce the internal defects of heavy plates and improve the defect detection level of heavy plate products. Also, The GTR process results in the formation of new crystal grains in the crack region, which is crucial to crack healing.

Simulation and Optimization of Cracked Gasoline Hydrofining Process

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Study on Hot Deformation Cracks of Steel D2 Using Processing Map

The hot deformation behaviors of steel D2 in the range of 900 ℃ to 1 160 ℃ and strain rate range of 0.01 s -1 to 10 s -1 have been studied by using Processing Map developed on the basis of dynamic materials model. The efficiency of energy dissipation η is taken as a function of temperature and strain rate to obtain a Processing Map. In the Processing Map of steel D2, there are two zones of cracking susceptivity with high dissipation efficiency η of 46 % and 63 % respectively. One zone is in the range of 900 ℃ to 980 ℃ and the strain rate range of 0.01 s -1 to 0.06 s -1 , and the other from 1 140 ℃ to 1 160 ℃ and 8 s -1 to 10 s -1 . The experiment proves that there are microstructural brittle transgranular fractures and macroscopic thermal cracks in the two zones respectively. The map also revealed that deformation in these two zones is of instable flowing , so these two zones should be avoided when choosing hot deformation conditions.

Dynamic experimental study on rock meso-cracks growth by digital image processing technique

A new meso-mechanical testing scheme based on SEM was developed to carry out the experiment of microfracturing process of rocks. The microfracturing process of the pre-crack marble sample on surrounding rock in the immerged Long-big tunnel in Jinping Cascade II Hydropower Station under uniaxial compression was recorded by using the testing scheme. According to the stereology theory, the propagation and coalescent of cracks at meso-scale were quantitatively investigated with digital technology. Therefore, the basic geometric information of rock microcracks such as area, angle, length, width, perimeter, was obtained from binary images after segmentation. The failure mechanism of specimen under uniaxial compression with the quantitative information was studied from macro and microscopic point of view. The results show that the image of microfracturing process of the specimen can be observed and recorded digitally. During the damage of the specimen, the distribution of microcracks in the specimen is still subjected to exponential distribution with some microcracks concentrated in certain regions. Finally, the change law of the fractal dimension of the local element in marble sample under different external load conditions is obtained by means of the statistical calculation of the fractal dimension.

ANALYSIS OF SURFACE CRACK ON FORWARD EXTRUDING BAR DURING AXISYMMETRIC CUP-BAR COMBINED EXTRUSION PROCESS

In this paper, the kinematically admissible velocity field with surface crack on forward extruding bar is put forward during the axisymmetric cup-bar combined extrusion process, in accordance with the results of model experiments.On the basis of velocity field, the necessary condition for surface crack formation on the forward extruding bar is derived, with the help of upper bound theorem and the minimum energy principle. Meanwhile, the relationships between surface crack formation and combination of reduction in area for the part of forward and backward extursions relative residual thickness of billet (T/R0),frictional factor (m) or relative land length of ram and chamber are calculated during the extrusion process. Therefore, whether the surface crack on forward exturding bar occurs can be predicted before extruding the lower-plasticity metals for axisymmetric cup-bar combined extrusion process.The analytical results agree very well with experimental results of aluminium alloy LY12 (ASTM 2024) and LC4 (ASTM 7075).

混凝土大坝活动裂纹电磁监测系统研制

为解决混凝土大坝活动裂纹识别成功率低、监测难度大的技术问题,提出一种新型混凝土大坝活动裂纹电磁监测系统。该电磁监测系统利用电磁监测传感器将混凝土大坝活动裂纹产生的微弱电磁辐射信号转化为电压信号,搭建信号调理模块实现10 kHz~1 MHz频段的微弱电压信号的多级放大和滤波,借助无线通信模块和云平台实现电磁辐射信号的无线传输和云端存储,在中控模块中采用LabVIEW构建软件系统,识别和监测活动裂纹电磁辐射信号,定位活动裂纹位置。通过实验确定了电磁监测系统的信噪比和定位误差,实验结果表明所研制的电磁监测系统可监测在传感器2 m范围内的混凝土大坝活动裂纹,为混凝土大坝的安全稳定运行提供保障。

聚硅氮烷热裂解过程中的有机-无机转化特性

为了探究聚硅氮烷(Polysilazane, PSZ)热裂解过程中的有机-无机转化特性,以甲基氢二氯硅烷和二甲基二氯硅烷为原料,通过氨解、热聚合制得PSZ;利用FT-IR、TG-DTA、PY/GC/MS等测试手段对PSZ的热裂解性能进行表征分析,并探讨不同热解温度下PSZ的组成结构及可能发生的化学反应。结果表明:PSZ以Si—N—Si为骨架,Si—H、N—H及Si—CH_(3)键为侧基,随着温度的升高,有机基团的吸收峰减弱。根据TG-DTA、PY/GC/MS的测试结果可以将PSZ热分解过程可以分为两个阶段:第一阶段为184~395℃,质量损失20.80%,该阶段包含了大部分化学反应及挥发性裂解产物的逸散,主要发生了的交联反应、重排反应及环化反应等,产生了NH_(4)、C_(6)H_(21)CH_(3)N_(3)Si_(3)及C_(8)H_(28)N_(4)Si_(4)等气体物质,350℃时PSZ中已基本完成交联反应;第二阶段为395~800℃,质量损失17.80%,在400℃时主要为大分子气体产物的挥发,500℃时PSZ中的有机官能团分解断裂成小分子物质逸出,并发生热解重排,正在逐渐向无机物转化,800℃时样品完成无机转变。研究结果可为聚硅氮烷纤维热分解工艺的设计和优化提供理论依据,对高性能陶瓷材料的制备有一定参考价值。

基于改进YOLOv8的轻量化中小桥梁裂缝检测方法

近年来,中国桥梁建设空前发展,桥梁安全运维问题日益凸显。文章提出一种基于YOLOv8的裂缝检测模型YOLOv8-BC,该模型采用GhostConv对HGNetv2改进后的结构替换YOLOv8的主干网络,实现模型轻量化;引入可变形注意力机制DAttention,获得更多的空间信息;使用基于辅助边框的Inner-iou损失函数替代CIOU损失函数,提高模型的泛化能力和检测精度。在自建数据集上进行实验,结果表明YOLOv8-BC模型准确率达到了95.3%,mAP50达到了95.9%,相较于YOLOv8s模型分别提高了2.3%和2.0%,同时参数量降低了15.3%。这表明YOLOv8-BC模型能够更高效地检测复杂环境下的桥梁裂缝,为工业检测提供了重要思路和技术支持。

Characterization of Loading Rate Effects on the Interactions Between Crack Growth and Inclusions in Cementitious Material

The microcapsule-enabled cementitious material is an appealing building material and it has been attracting increasing research interest.By considering microcapsules as dissimilar inclusions in the material,this paper employs the discrete element method(DEM)to study the effects of loading rates on the fracturing behavior of cementitious specimens containing the inclusion and the crack.The numerical model was first developed and validated based on experimental results.It is then used to systematically study the initiation,the propagation and the coalescence of cracks in inclusion-enabled cementitious materials.The study reveals that the crack propagation speed,the first crack initiation stress,the coalescence stress,the compressive strength and the ultimate strain increase with the loading rate.The initiation position,the propagation direction,the cracking length and the type of the initiated cracks are influenced by the loading rates.Two new crack coalescence patterns are observed.It is easier to cause the coalescence between the circular void and a propagating crack at a slow loading rate than at a fast loading rate.

某试验器排气段裂纹及补焊可行性分析

牌号为06Cr19Ni10是常用的奥氏体不锈钢,在各行业应用非常广泛,具有良好的工艺性能、耐腐蚀性,使用温度范围在-196℃~800℃。某试验器排气段产生了裂纹现象,通过对母材取样以及补焊试件进行金相组织、力学性能等分析,总结了裂纹产生的原因并制定合理的补焊工艺、加装支架等措施来确保补焊质量并提高系统的可靠性。通过一年多稳定的试验运行,得出焊接修复以及优化是行之有效的结论。

The Interaction between Microcapsules with Different Sizes and Propagating Cracks

The microcapsule-contained self-healing materials are appealing since they can heal the cracks automatically and be effective for a long time.Although many experiments have been carried out,the influence of the size of microcapsules on the self-healing effect is still not well investigated.This study uses the two-dimensional discrete element method(DEM)to investigate the interaction between one microcapsule and one microcrack.The influence of the size of microcapsules is considered.The potential healing time and the influence of the initial damage are studied.The results indicate that the coalescence crack is affected by the size of holes.The elastic modulus,the compressive strength and the coalescence stress decrease with the rising radius of holes.The initial damage in experiments should be greater than 95%of the compressive strength to enhance the self-healing effect.The large microcapsules require slight initial damage.Both a new type of displacement field near the crack and a new category of coalescence crack are observed.The influence of sizes of holes on the cracking behavior of concrete with a circular hole and a pre-existing crack is clarified.

Distribution and State of Ni Contaminants on Resid Fluid Catalytic Cracking Catalysts—Characterization by AEM, EPMA, UV-Vis and TPR

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Research Progress in Catalytic Cracking Reaction of Tetralin and Decalin

The integrated catalytic hydrogenation and catalytic cracking process has been gradually adopted by refineries to satisfy the requirements for manufacture of light and clean petroleum products. To explore the reaction laws of hydrogenated aromatics in hydrotreated oil, the catalytic cracking reaction laws of hydrogenated aromatics have been reviewed by taking tetralin and decalin as examples of different degrees of hydrogenated aromatics. Moreover, the reaction mechanism of tetralin and decalin has been analyzed emphatically. The effects of zeolite pore structure, acid properties and process parameters on reaction laws have been analyzed carefully. It is considered that the catalytic cracking performance of hydrogenated aromatics with different hydrogen saturation degrees is quite different. It is necessary to control the hydrogenation depth, optimize the hydrocarbon composition of catalytic cracking feed materials for maximizing the yield of target products.

Modeling and simulation of 3D thermal stresses of large-sized castings in solidification processes

When heavy machines and large scaled receiver system of communication equipment are manufactured, it always needs to produce large-sized steel castings, aluminum castings and etc. Some defects of hot cracking by thermal stress often appear during solidification process as these castings are produced, which results in failure of castings. Therefore predicting the effects of technological parameters for production of castings on the thermal stress during solidification process becomes an important means. In this paper, the mathematical models have been established and numerical calculation of temperature fields by using finite difference method (FDM) and then thermal stress fields by using finite element method (FEM) during solidification process of castings have been carried out. The technological parameters of production have been optimized by the results of calculation and the defects of hot cracking have been eliminated. Modeling and simulation of 3D thermal stress during solidification processes of large-sized castings provided a scientific basis, which promoted further development of advanced manufacturing technique.

Corrosion fatigue behavior of fastening hole structure and virtual crack propagation tests

The fatigue crack propagation behavior of the LY12CZ aluminum alloy fastener involving a central hole in air or in 3.5wt% NaCl solution was investigated. The experimental results indicated that the corrosion fatigue crack growth rate decreased with the increasing loading frequency,and in a corrosive environment,the crack growth rate was slightly larger than that in air. Based on the experimental results,the virtual corrosion fatigue crack propagation tests were investigated and the stochastic process method and the AFGROW simulation method were presented. The normal process and lognormal process were considered for the stochastic process method based on the numerically fitted Paris equation. The distribution of crack size and the corresponding probabilistic model of crack length distribution for a given number of cycles can be found by integrating the stochastic process over time. Using the AFGROW software,the virtual simulation was carried out to analyze the corrosion fatigue crack growth behavior and the predicted crack growth curve was in good agreement with the experimental results.

Cold Cracking of Flux Cored Arc Welded Armour Grade High Strength Steel Weldments

In this investigation, an attempt has been made to study the influence of welding consumables on the factors that influence cold cracking of armour grade quenched and tempered （Q＆.T） steel welds. Flux cored arc welding （FCAW） process were used making welds using austenitic stainless steel （ASS） and low hydrogen ferritic steel （LHF） consumables. The diffusible hydrogen levels in the weld metal of the ASS and LHF consumables were determined by mercury method. Residual stresses were evaluated using X-ray stress analyzer and implant test was carried out to study the cold cracking of the welds. Results indicate that ASS welds offer a greater resistance to cold cracking of armour grade Q＆T steel welds.

Stability analysis of the sliding process of the west slope in Buzhaoba Open-Pit Mine

To study the stability of the west slope in Buzhaoba Open-Pit Mine and determine the aging stability coefficient during slide mass development, the deformation band of the west slope and the slide mass structure of the 34,600 profile are obtained on the basis of hydrology, geology, and monitoring data.The residual thrust method is utilized to calculate the stability coefficients, which are 1.225 and 1.00 under sound and transfixion conditions, respectively. According to the rock damage and fragmentation and the principle of mechanical parameter degradation, the mechanical models of the slide mass development of the hard and soft rock slopes are established. An integrated model for calculating the slope stability coefficient is built considering water, vibration, and other external factors that pertain to the structural plane damage mechanism and the generating mechanism of the sliding mass. The change curve of the stability coefficient in the slide mass development is obtained from the relevant analyses,and afterwards, the stability control measures are proposed. The analysis results indicate that in the cracking stage of the hard rock, the slope stability coefficient decreases linearly with the increase in the length Lbof the hard rock crack zone. The linear slope is positively correlated to rock cohesion c. In the transfixion stage of the soft rock, the decrease speed of the stability coefficient is positively correlated to the residual strength of the soft rock. When the slope is stable, the stability coefficient is in a quadratic-linear relationship with the decreased height Dh of the side slope and in a linear relationship with anchoring force P.