crack

摘要： An accurate and straightforward symplectic method is presented for the fracture analysis of fractional two-dimensional(2D)viscoelastic media.The fractional Kelvin-Zener constitutive model is used to describe the time-dependent behavior of viscoelastic materials.Within the framework of symplectic elasticity,the governing equations in the Hamiltonian form for the frequency domain(s-domain)can be directly and rigorously calculated.In the s-domain,the analytical solutions of the displacement and stress fields are constructed by superposing the symplectic eigensolutions without any trial function,and the explicit expressions of the intensity factors and J-integral are derived simultaneously.Comparison studies are provided to validate the accuracy and effectiveness of the present solutions.A detailed analysis is made to reveal the effects of viscoelastic parameters and applied loads on the intensity factors and J-integral.

摘要： Human motion detection needs sensors with flexibility,high sensitivity and linearity.However,conventional strain sensors are rigid and not suitable for human motion detection applications.Graphene-based strain sensors can overcome the above challenges but currently are still in the infancy of their development.In this work,properties of graphene-based crack-type strain sensors are investigated and guidelines to improve the sensitivity of graphene films as sensing elements are developed.First,it is found that the pre-strains influences the crack morphology and density,which further results in different sensor sensitivities and linearity.Second,the graphene film thickness influences the crack density due to the sliding between graphene layers;namely,a thinner graphene film with more cracks exhibits higher sensitivity.Third,the substrate influences the bonding strength with the graphene film,leading to different crack formations,which results in adjusted sensitivity.The cracks on PDMS are channel cracks while those on epoxy are isolated short cracks.The channel cracks are preferred to cause high sensitivity while the isolated short cracks hardly have a blocking effect on the current transport.Finally,the optimized graphene strain sensors are used to detect various human motions and exhibit high sensitivity.

摘要： Concrete is the most widely used composite material in civil engineering.Microbial induced calcium carbonate precipitation(MICP)is a green and environmental friendly technology,which has received extensive attention in repair of concrete cracks.This paper introduces the research progress in Southeast University research in past 16 years.In the early stage,MICP technology of urea hydrolyzed by Bacillus pasteurii was mainly investigated to repair the surface cracks and to fill large-size cracks with grouting.However,aiming at the hidden cracks that were difficult for human intervention,a new mineralization route of Bacillus mucilaginosus was proposed,which could repair faster than Bacillus alcalophilus,and the problem of ammonia emission in the repair process of Bacillus pasteurii was also solved.In addition,in order to improve the protection of bacteria and the self-healing efficiency of the later age cracks,the methods of fiber immobilization,carrier uniformly immobilization and core-shell structural immobilization had been compared and studied.The results showed that core-shell structural immobilization had good protection ability and strong designability.What’s more,the paper also summarized the characteristics of spore germination,cell activity,nucleation and biological calcium carbonate in crack zone,and introduced the application experience of microbial self-healing concrete in water conservancy projects and subway stations.

摘要： Industry design standards such as BS 7910 deployed some empirical formulas for the prediction of stress intensity factor(SIF) based on simulation results from traditional finite element method(FEM).However,such FEM simulation occasionally failed to convince people due to the large discrepancies compared with engineering practice.As a consequence,inaccuracy predictions via such formulas in engineering standards inevitably occur,which will compromise the safety of structures.In our previous research work,an abnormal phenomenon of SIF in a cracked T-butt joint accounting for welding effect has been observed.Compared with BS 7910,the calculation results of SIF at the surface points of welded specimens cannot be well predicted,with a large discrepancy appearing.In order to explore such problem with an abnormal increase at the surface points of cracked welded specimens,a numerical investigation in terms of SIF among BS 7910,XFEM,and FEM is performed in this paper.Numerical models on both a simple cracked plate without welding effect and a cracked T-butt joint with welding effect are developed through ABAQUS.Parametric studies in terms of the effects of varied crack depth to thickness ratio(a/T) and the effects of crack depth to crack half-length ratio(a/c) are carried out.Empirical solutions from BS 7910 are used for comparison.It is found that the XFEM can provide predictions of SIF at both the crack deepest point and crack surface point of a simple cracked plate as accurate as FEM.For a T-butt joint with a transverse stiffener,a large discrepancy in terms of the weld magnification factors(Mk) occurs at the crack surface point compared with empirical predictions.An exceptional increase of von Mises stress gradient in regions close to the weld-toe is found through the simulation of FEM,whereas a constant stress gradient is obtained through XFEM.The comparison results indicate an inappropriate prediction of SIF by the utilization of the empirical formulas in BS 7910.A more reasonable prediction of the SIF at the surface point of a crack is obtained by the XFEM.Therefore,further updating of the empirical solutions in BS7910 for SIF accounting for welding effect is recommended.

摘要： This paper focuses on methodological issues relevant to corrosion risk prediction models.A model was developed for the prediction of corrosion rates associated with hot-dip galvanised reinforcement bar material in concrete exposed to carbonation and chlorides in outdoor environment.One-year follow-up experiments,over five years,were conducted at various carbonation depths and chloride contents.The observed dependence of corrosion rate on the depth of carbonation and chloride content is complex indicating that the interaction between the carbonation and chloride influencing the corrosion.A non-linear corrosion model was proposed with statistical analysis to model the relationship between the corrosion rate and the test parameters.The main methodological contributions are(i)the proposed modeling approach able to take into account the uncertain measurement errors including unobserved systematic and random heterogeneity over different measured specimens and correlation for the same specimen across different measuring times,which best suits the measurement data;(ii)the developed model in which an interaction parameter is introduced especially to account for the contribution and the degree of the unobserved carbonation-chloride interaction.The proposed model offers greater flexibility for the modelling of measurement data than traditional models.

摘要： In recent years,China''s social economy is in a period of rapid development which has also made great progress in the construction of roads and bridges.Roads and bridges as basic building facilities provides strong support for local transportation and socioeconomic development in China.At this stage,roads and bridges are the basic guarantee for the development of the national economy,so great attention must be paid to the quality of their construction and engineering design.At present,the main factor affecting the quality of road bridges in China is the problem of bridge cracks.There are various reasons causes for cracks they must be controlled by effective measures to better improve the quality of road bridges.This article will discuss crack control in road bridge design and construction.

摘要： cqvip:Sensitivity of Nb to high-temperature ductility dip crack(HTDDC) of deposited metal of Inconel 690 welding wire was studied in detail. Strain to fracture test and high-temperature tensile test were selected as the test methods to study the sensitivity of HTDDC. The deposited metals of four kinds of welding wire were observed and analyzed by OM and SEM. Experiment results show that Nb can effectively improve the ability of Inconel 690 to resist HTDDC and reduce the crack sensitivity of deposited metal. The mechanism of HTDDC is the grain boundary strength of deposited metal is lower than the intragranular strength. The(Nb, Ti) C can effectively block the grain boundary sliding and improve the resistance to deformation of the grain boundary.

摘要： Pulse excitation or vibration stimulation was imposed on the low permeable formation with cracks to enhance the production or injection capacity.During that process,a coupling of wave-induced flow and initial flow in dual-porous media was involved.Researchers had done much work on the rule of wave propagation in fractured porous media,whereas attentions on the variation law of flow in developing low permeable formation with cracks under vibration stimulation were not paid.In this study,the effect of low-frequency vibration on the seepage in dual-porous media was examined for the application of wave stimulation technology in developing reservoirs with natural cracks.A model for seepage of single-phase liquid in porous media with cracks under low-frequency vibration excitation was built by combining wave propagating theory for porous media with cracks and dual-porous media seepage mechanics.A governing equation group for the model,which was expressed by dimensionless fluid and solid displacements,was derived and solved with a numerical method.Variable physical properties were simulated to check the applicability of external low-frequency vibration load on dual-porous media and a parametric study for various vibration parameters.Stimulation of low-frequency vibration affected flow velocities of crack and rock matrix fluids.Compared with that in single-porous media,the stimulation effect on the fluid inner matrix of dual-porous media was relatively weakened.Different optimal vibration parameters were needed to increase the channeling flow between the crack and rock matrix or to only promote the flow velocity in the rock matrix.The theoretical study examines wave-coupled seepage field in fractured porous media with results that are applicable for low-frequency stimulation technology.

摘要： In order to resolve the safety problem of the existing crane runway gir-ders(CRGs)with defects,the constraint-based R6 criterion is proposed to assess their structural integrity.The ex isting steel CRGs with defects at the weld joint between the upper flange and web plate,are characterized to three-dimensional finite element models with a semi-ellipse surface crack.The R6 criterion has been modified by considering the constraint effect which is represented by T-stress.The analysis results ilustrate that working condition of the cracked CRGs leads to high constraint level along the crack front.The crack aspect ratio(a/c)and run-way eccentricity(e)have significant influence on the integrity of the cracked CRGs.The integrity assessment results based on modified constraint-based R6 failure criterion enable to more effectively protect the cracked CRGs from brittle fracture failure.

摘要： In this study,a new bond-based peridynamic model is proposed to describe the dynamic properties of ceramics under impact loading.Ceramic materials show pseudo-plastic behavior under certain compressive loadings with high strain-rate,while the characteristic brittleness of the material dominates when it is subjected to tensile loading.In this model,brittle response under tension,softening plasticity under compression and strain-rate effect of ceramics are considered,which makes it possible to accurately capture the overall dynamic process of ceramics.This enables the investigation of the fracture mechanism for ceramic materials,during ballistic impact,in more detail.Furthermore,a bond-force updating algorithm is introduced to perform the numerical simulation and solve the derived equations.The proposed model is then used to analyze the dynamic response of ceramics tiles under impact loading to assess its validity.The results of damage development in ceramic materials are calculated and compared with the experimental results.The simulation results are consistent with the experiments,which indicates that the proposed rate-dependent peridynamic model has the capability to describe damage propagation in ceramics with good accuracy.Finally,based on a comparison between simulation and experimental results,it can be concluded that the damage results are in better agreement with experimental results than non-ordinary state-based peridynamic method.

摘要： High-speed injection die casting is a technology witch is effective for upgrading of Aluminum die-cast products，but it sometimes makes problems such as damage of die in early period，because of a larger load on the molding die compared with conventional technology．Then，we investigated，to find the cause of generation of damage made by using Super high-speed injection，withthe results of observation of the dies and CAE (die temperature analysis，thermal stress analysis)．In this paper，we report on the investigation results and the countermeasures to solve above the problems．

摘要： High-speed injection die casting is a technology witch is effective for upgrading of Aluminum die-cast products，but it sometimes makes problems such as damage of die in early period，because of a larger load on the molding die compared with conventional technology．Then，we investigated，to find the cause of generation of damage made by using Super high-speed injection，withthe results of observation of the dies and CAE (die temperature analysis，thermal stress analysis)．In this paper，we report on the investigation results and the countermeasures to solve above the problems．

摘要： High-speed injection die casting is a technology witch is effective for upgrading of Aluminum die-cast products，but it sometimes makes problems such as damage of die in early period，because of a larger load on the molding die compared with conventional technology．Then，we investigated，to find the cause of generation of damage made by using Super high-speed injection，withthe results of observation of the dies and CAE (die temperature analysis，thermal stress analysis)．In this paper，we report on the investigation results and the countermeasures to solve above the problems．

摘要： 本发明公开了一种改善Flip chip基板翘曲、bump桥接和Die crack的治具，包括：压板，所述压板上形成有多个镂空设置的焊接区域，多个所述焊接区域以外的部分形成所述压板的板框，所述板框通过固定组件固定在基板与倒装芯片待焊接的一侧，且所述板框将所述基板覆盖。通过对基板上单个待焊接倒装芯片以外的部分通过压板进行固定，增加基板被压固的区域，可以减小回流焊后基板的翘曲、凸点之间桥接以及芯片破裂而引起的焊接不良的问题。

摘要： 本发明公开了一种改善弹坑crack产生的生产设计方法，包括以下步骤，步骤1，对机台进行机差校准；步骤2，已校准的机台进行加工试机产品；步骤3，确认试机产品的加工质量，依据试机产品弹坑焊丝的线径调整机台加工参数，增加取样比例进行机台弹坑buyoff；步骤4，对取样产品进行实验室切片，确认机台输出对弹坑的影响；步骤5，依据步骤4的影响结果，修改生产设备的生产参数，开始生产。通过对机台输出一致性进行校准和识别产品弹坑Crackprocess window，识别出优选机台，将优选机台信息录入CIM系统与产品绑定，保证产品只在识别出的优选机台上作业，减少弹坑Crack发生的机率。