爆破方案对硐室爆破成本的影响

本文讨论了爆破方案对硐室爆破成本的影响情况。     

100 m高烟囱定向爆破拆除

较详细地介绍了广州恒运电厂100m高钢筋混凝土烟囱的定向爆破设计与施工,并对爆破过程中的支座破坏及爆破效果进行了分析,对如何中确保高烟囱准确的提出了自己的看法,对于类似工种的设计与施工具有一定的参考价值。     

复杂环境下楼房的控制爆破拆除

本文介绍了在复杂环境下一栋五层砖混结构大楼的爆破拆除,并对爆破方案的选择,参数的选取进行了分析和论述,可供类似工程参考。     

光面、预裂爆破参数选择与质量措施研究

爆破参数的选择直接影响着爆破效果,是光面,预裂爆破工程设计的重要内容。本文结合工程实践,给出光面,预裂爆破的参数计算公式和一些参考值,并对确保光面,预裂爆破质量的技术措施进行了归纳总结。     

用水压爆破方法拆除澄清池

根据拆除物的结构特点，进行了澄清池水压爆破的设计计算。利用等效药量与等效距离对爆破近区的振动强度进行了验算。     

砖烟囱控爆拆除与倾倒观测

介绍了在复杂环境条件下砖烟囱爆破拆除的设计与爆破效果,对烟囱的倾倒过程、爆渣堆积范围进行了详细讨论。     

54.5 m 高工业厂房的控制爆破拆除

简单阐述了对高度为54．5m、框架剪力墙结构的工业厂房进行爆破拆除中的工程概况、爆破方案、防护措施、爆破效果及爆破后的体会，对今后类似工程具有一定的参考价值。     

泥土爆破

1 泥土爆破的特征把土壤或近似于粘土的软岩的爆破称为泥土爆破。这种泥土爆破的应用有开沟爆破除根爆破及深耕爆破等。一般平整宅地时对硬土层及夹杂有粘土的凝灰岩进行的爆破也属于泥土爆破,然而,近年来由于机械设备的发展,几乎不再依靠这种爆破方法。由于土壤、粘土等是和硬质岩石类弹性体不同的凝集物,所以依靠炸药爆炸产生的冲击波的爆破效果不高;主要是依靠爆炸产生的气体膨胀使土壤、粘土等搬移的爆破。换句话说,泥土爆破就是利用炸药的爆炸把土壤、粘土等“搬家”的爆破,爆破效果主要受炸药静的威力的支配。     

普通导爆索在高温爆破中的应用

本文叙述了导爆索在高温炮孔受热后的感度变化,测定了导爆索受热后的爆速和对防自爆药包的起爆能力,对普通导爆索用于高温爆破进行了论证。     

新型电力无声爆破技术

本文通过具体的现场试验,介绍了一种新的无声爆破技术,并对该技术的发展前景作了可行性分析.     

Algorithmic implementation of a generalized cohesive crack model

Smeared fictitious crack models can be regarded as generalized cohesive crack models. The classic fictitious crack models, i.e. the fixed crack, multiple fixed crack, rotating crack and microplane model, are based on different assumptions for the orientation of developing cracks. A smooth transition between the extreme cases, the fixed crack and the rotating crack model, is provided by the adaptive fixed crack model. In this approach, the critical direction of failure is uniquely identified based on Mohr's hypothesis. Thus, the critical direction depends on the character of the failure criterion and the type of loading. The numeric implementation of the adaptive fixed crack model has given rise to some subtle questions. It is shown that even for a classical fixed crack concept, the algorithmic tangent stiffness may have to include components of crack rotation, depending on the imposed strategy for the global equilibrium iteration scheme.     

GH4169合金焊接接头高温疲劳裂纹扩展性能试验研究

对GH4169合金焊接接头在650℃下的疲劳裂纹扩展性能进行了测试和分析.结果表明,疲劳裂纹扩展速率、初始裂纹尺寸、裂纹容限和温度对焊接接头的疲劳裂纹扩展寿命都有影响.母材及焊缝的疲劳裂纹扩展速率和裂纹容限均有较大的差异.     

Mixed-mode fatigue crack growth under biaxial loading

Studies on crack growth in a panel with an inclined crack subjected to biaxial tensile fatigue loading are presented. The strain energy density factor approach is used to characterize the fatigue crack growth. The crack growth trajectory as a function of the initial crack angle and the biaxiality ratio is also predicted. The analysis is applied to 7075-T6 aluminium alloy to predict the dependence of crack growth rate on the crack angle. The effect of crack angle on the cyclic life of the component and on the cyclic life ratio is presented and discussed.     

Measurement of crack closure after the application of an overload cycle, using moiré interferometry

The crack closure behaviour on the application of a single overload cycle was studied in a Ti-6Al-4V specimen. Moiré interferometry with photoresist gratings was used to measure crack displacements. During the overload cycle a large crack opening displacement was observed at the maximum load. This was similar to predictions from a Dugdale-type crack closure model. When the load was taken back to zero, the crack was open at the crack tip due to the high levels of plastic deformation during the overload cycle. As the crack was grown there was some evidence of the deformed material on the crack faces.Moiré interferometry provided displacement data close to the crack faces, even when the crack had grown to over two-and-a-half times the overload crack length. When the overload was applied the crack bifurcated, and the Dugdale-type model under-predicted the crack opening.     

Ultrasonic Measurement of the Crack Depth and the Crack Opening Stress Intensity Factor Under a No Load Condition

This paper describes a new methodology for evaluating the crack depth and the crack opening stress intensity factor of small closed cracks using an ultrasonic technique. Surface connected back-wall cracks of depth ranging from 0.4 to 4.0 mm in steel specimens are considered. The crack corner echo amplitude of an ultrasonic shear wave, SW, beam of 50° incidence in material is used. First, the ultrasonic echo response of an open crack is determined as a function of crack depth. Next, based on changing the crack closure stress, an empirical relation between the crack closure stress and the crack-echo response is formulated. The crack depth and the crack closure stress of an unknown closed crack based on these relations are determined by inverse analysis of the ultrasonic response of the crack. From the evaluated crack depth and crack closure stress, the crack opening stress intensity factor is determined. The accuracy and reliability of this new nondestructive evaluation (NDE) method is verified by comparing the evaluated crack depth with the actual one. The latter is measured on the fractured surface obtained after carrying out ultrasonic testing. The ultrasonic method developed is proved to be a powerful tool for quantitative and nondestructive evaluation of the crack depth as well as the crack closure stress.     

UNSTABLE AND STABLE CRACK GROWTH: IMPLICATIONS FOR THE BEHAVIOUR OF SMALL AND LONG FATIGUE CRACKS

Abstract— The effects of the changes of crack shapes on the behaviour of small cracks were investigated on single edge crack specimens and small surface crack specimens with different initial crack shapes. Experimental results obtained from beach mark measurements on the fracture surfaces indicated that the behaviour of small cracks was strongly dependent on the crack shape itself. While the initial shape of a small crack was unstable with respect to the state of specimen-geometry-stress system, the crack gradually adjusted its shape to a specific preferred shape by means of non-uniform growth. In addition, the deceleration and subsequent acceleration of crack growth corresponds to the transition from unstable to stable crack growth.     

The anisotropic R-criterion for crack initiation

The anisotropic nature of mixed modes I-II crack tip plastic core region and crack initiation is investigated in this study using an angled crack plate problem under various loading conditions. Hill’s anisotropic yield criterion along with singular elastic stress field at the crack tip is employed to obtain the non-dimensional variable-radius crack tip plastic core region. In addition, the R-criterion for crack initiation proposed by the authors for isotropic materials is also extended to include anisotropy. The effect of Hill’s anisotropic constants on the shape and size of the crack tip plastic core region and crack initiation angle is presented for both plane stress and plane strain conditions at the crack tip. The study shows a significant effect of anisotropy on the crack tip core region and crack initiation angle and calls for further development of anisotropic crack initiation theory.     

Why do cracks branch? A peridynamic investigation of dynamic brittle fracture

In this paper we review the peridynamic model for brittle fracture and use it to investigate crack branching in brittle homogeneous and isotropic materials. The peridynamic simulations offer a possible explanation for the generation of dynamic instabilities in dynamic brittle crack growth and crack branching. We focus on two systems, glass and homalite, often used in crack branching experiments. After a brief review of theoretical and computational models on crack branching, we discuss the peridynamic model for dynamic fracture in linear elastic–brittle materials. Three loading types are used to investigate the role of stress waves interactions on crack propagation and branching. We analyze the influence of sample geometry on branching. Simulation results are compared with experimental ones in terms of crack patterns, propagation speed at branching and branching angles. The peridynamic results indicate that as stress intensity around the crack tip increases, stress waves pile-up against the material directly in front of the crack tip that moves against the advancing crack; this process “deflects” the strain energy away from the symmetry line and into the crack surfaces creating damage away from the crack line. This damage “migration”, seen as roughness on the crack surface in experiments, modifies, in turn, the strain energy landscape around the crack tip and leads to preferential crack growth directions that branch from the original crack line. We argue that nonlocality of damage growth is one key feature in modeling of the crack branching phenomenon in brittle fracture. The results show that, at least to first order, no ingredients beyond linear elasticity and a capable damage model are necessary to explain/predict crack branching in brittle homogeneous and isotropic materials.     

Experimental investigation of crack growth direction in multiple cracks

In this paper, the interaction between multiple cracks in crack growth direction is studied in an aluminium alloy under static and fatigue loading. Self similar as well as non‐self‐similar crack growth has been observed which depends on the relative crack positions defined by crack offset distance and crack tip distance. On the basis of experimental observations, the criterion for crack coalescence and crack growth direction are expressed in terms of the crack positions defined by crack offset and crack tip distances. The criterion presented in this study can be used to determine the limiting value of crack tip and crack offset distance and to determine the mode in which cracks coalesce during their growth process. Experimental results and crack interaction criterion presented under various crack positions and size conditions could be used to derive a new evaluation method of crack growth in multiple crack geometry.     

Investigation of crack tunneling in ductile materials

Crack tunneling has been commonly observed in crack growth experiments on specimens made of ductile materials such as steel and aluminum alloys. The objective of this study is to investigate the crack tunneling phenomenon and study the effects of crack tunneling on the distribution of several mechanics parameters controlling ductile fracture. Three-dimensional (3D) elastic-plastic finite element analyses of stable tearing experiments involving tunneling fracture are carried out. Two model problems based on stable tearing experiments are considered. The first model problem involves a plate specimen containing a stationary, single-edge crack with a straight or tunneled crack front, under remote mode I loading. In the numerical analyses, the crack tip opening displacement, the von Mises effective stress, the mean stress, the stress constraint and the effective plastic strain around straight and tunneled crack fronts are obtained and compared. It is found that crack tunneling produces significant changes in the stress and deformation fields around the crack front. The second model problem involves a specimen containing a stably growing single-edge crack with a straight or tunneled crack front, under remote mode I loading. Crack growth events with a straight or tunneled crack front are simulated using the finite element method, and the effect of crack tunneling on the prediction of the load-crack-extension response based on a CTOD fracture criterion is investigated.