Fracture Mechanics of Plate Debonding

This paper presents a fracture mechanics model to determine the load at which FRP plates will debond from reinforced concrete beams. This will obviate the need for finite-element analyses to be used in situations where there is an infinite stress concentration and where the exact details of the interface geometry and properties are unknowable. The paper shows how fracture mechanics concepts based on energy release rates, can be used to answer the question “Will this existing interface crack extend?” Possible modes of debonding are analyzed as is the effect of the plate curtailment location on the debonding mode.     

Fracture Mechanics of Rubber Epoxy Composites

The effect of the addition of rubber micro-particles to epoxy matrix on the mechanical properties and the fracture toughness were investigated. Rubber epoxy composites were prepared with different weight percentages namely, 0, 5, 10, 15, 20, 25, 30 wt pct of rubber. Both quasi-static and dynamic ultrasonic measurements of the elastic modulus were found to decrease by 60 pct, and the critical value of the stress intensity factors was found to increase by approximately 45 pct for the rubber epoxy composites. This was also confirmed with the finite element analysis that had the same increasing trend. The fracture surface morphology reveals rough cleavage fracture in the epoxy matrix with brittle intergranular decohesion caused by the impurity segregation that exhibits relatively high micro-roughness of the fracture surfaces.     

Nondestructive Defect Size Monitoring in Fracture Mechanics Studies

Abstract

In this article we will review three major NDT techniques which are in common use; optical, electrical resistance and ultrasonic. The field of activity of fracture mechanics can be divided into two major areas. First, laboratory studies, where COD samples (crack opening displacement) or K_IC type samples are examined, and field studies where real defects found in the structures are examined and fracture mechanics criteria applied.

Résumé

Cet article porte sur trois techniques majeures des methodes de controle non destructif qui sont en usage commun. Elles sont le controle visuel, à la résistance électrique et aux ultrasons. Le champ d'action de la mécanique de rupture peut se diviser en deux majeures parties. D'abord il y a les recherches de laboratoire alors que les échantillons 'COD' ou celles du type K_IC sont examinés, et ensuite il y a les études faites sur le chantier et où les défauts réels sont identifiés dans les structures à controller et alors que les criteria des mécaniques de rupture entrent en jeu.     

不同粒径胶结类岩石材料损伤模型研究

为研究岩石损伤特性与矿物颗粒之间的关系,对三种不同粒径石英砂组成的类岩石材料进行单轴压缩试验,分析类岩石材料力学特性;基于等价应变原理,建立不同粒径类岩石材料损伤本构方程,分析各粒径类岩石材料破裂过程损伤演化特性。研究结果表明:理论损伤本构方程和试验结果基本吻合。在0.1~1 mm粒径范围内,类岩石材料的单轴抗压强度、峰值变形比能与其内部粒径大小组成具有一定的关系:粒径越大,单轴抗压强度和峰值变形比能越小;试样在单轴压缩过程中,粒径越大,峰值应力前损伤值越大,峰值应力后粒径越小,损伤值增长越快,破坏越突然。     

Fracture in Equiaxed Two Phase Alloys: Part I. Fracture in Alloys with Isolated Elastic Particles

Fracture in equiaxed two phase alloys containing isolated elastic particles has been analyzed from the viewpoint of a recently proposed model for fracture initiation and propagation in such materials. This model predicts fracture toughness parameters in terms of the microstructural geometry, relative phase volume fractions, and tensile properties of the materials. Predictions of the model are tested experimentally for two phase Co-CoAl alloys over a wide range of compositions, and the results indicate good agreement between predicted and observed fracture toughnesses. M. A. PRZYSTUPA, formerly Graduate Research Assistant, Department of Metallurgical Engineering, Michigan Technological University.     

Nutrient Loads Associated with Different Sediment Sizes in Urban Stormwater and Surface Pollutants

A significant amount of pollutants in urban stormwater runoff is transported as sediment-bound contaminants. It is important to have a clear understanding of the amount of pollutants attached to the different sediment sizes so that treatment facilities can be designed to effectively target the removal of the most polluted sediment sizes. This paper presents results from a study carried out to determine nutrient loads associated with different particle size ranges for dry surface pollutants and stormwater samples collected from an urban road surface. The results indicate that although more that half of the surface pollutant is coarser than 300 μm (microns), less than 15% of the total phosphorus (TP) and total nitrogen (TN) are attached to particle sizes greater than 300 μm. The pollutant loads in the different particle size ranges from different stormwater samples show a larger variability for TN than for TP. The dissolved component for TN ranges between 20 and 50% compared to 20–30% for TP. Practically all the particulate TP and TN in stormwater samples are attached to sediments between 11 and 150 μm. This suggests that to effectively remove TP and TN, pollutant treatment facilities must be able to remove particulates down to 11 μm.     

Dynamic Fracture of a Zr-based Bulk Metallic Glass

In the present study, dynamic fracture experiments are performed on fully amorphous Liquidmetal-1 (LM-1), a Zr-based BMG, to better understand fracture initiation and propagation in notched specimens. Experiments are conducted on notched (110 μm notch radius) four-point bend specimens using an instrumented modified split-Hopkinson pressure bar apparatus. The results of these experiments suggest that the critical dynamic stress intensity factor achieved by the notched LM-1 specimens is ~110 MPa m^1/2, which is similar to the fracture toughness determined from previous quasi-static fracture experiments. This insensitivity of the fracture toughness to crack tip loading rate suggests negligible loading-rate sensitivity on the dynamic fracture initiation toughness in LM-1. In situ high-speed camera images of the notched sample during the dynamic loading process show multiple fracture initiation attempts and subsequent arrests prior to catastrophic fracture initiation. Controlled stress wave loading experiments designed to induce sub-critical levels of damage in the notched specimens show extensive deformation banding extending 150 to 200 μm outward from the notch. The deformation bands, nominally perpendicular to each other, run along the direction of the notch and perpendicular to it. They are consistent with slip-line fields in notched samples of elastic perfectly plastic materials. Subsequent loading of the damaged specimen again shows several attempts at crack initiation followed by blunting; the initial sub-critical damage in the region around the notch is understood to increase the energy required for catastrophic specimen failure and is consistent with an increase in the effective notch radius due to preexisting damage.     

应用断裂力学分析铬钼钢的热疲劳特性

通过试验分析了2．25Cr-1Mo钢的同相和异相热疲劳特性,并应用弹塑性断裂力学方法对其寿命作了解析评价。试验和计算都表明,在相同应变范围下,同相热疲劳的寿命低于异相。另外,计算值和试验值吻合,说明J积分用作评价Cr-Mo钢热疲劳强度的力学参数及本文所建立的计算方法有效。作者还从能量角度提出了一个用于描述裂纹扩展能力的参数△W。在相同△W值下。同相热疲劳寿命和异相热疲劳寿命相等。     

Critical Shear Offset of Fracture in a Zr-based Metallic Glass

The nanoscale shear band operation process of Zr_(55)Pd_(10)Cu_(20)Ni_5Al_(10) metallic glass(MG)was reined in by constant force during well-designed loading-holding-unloading cyclic microcompression test.Through the test,it is revealed that the whole shear banding process involves three stages:shear band initiation,shear sliding and shear band arrest.Based on the energy balance principle,the size-affected speed of shear sliding is interpreted.The energy originated from the shear sliding leads to heat-up of the shear plane;therefore,the temperature in shear band increases with the size of shear offset caused by the energy accumulation during shear sliding.Taking the glass transition temperature as the critical temperature of fracture for the Zr-based MG,the critical shear offset is predicted to be approximately 190μm,fully in line with the experimental observation.This directly proved that the fracture of the MG is caused by the temperature rise during shear sliding.     

The Duality of Fracture Behavior in a Ca-based Bulk-Metallic Glass

Ca₆₅Mg₁₅Zn₂₀ bulk-metallic glass (BMG) exhibited a typical brittle fracture behavior during compressive loading at room temperature. Samples exploded into many small pieces after elastic deformation and no macroscopic plasticity was observed. The fracture surface demonstrated multiple fracture patterns, including typical metallic-glass vein patterns and glass mirror, mist, and hackle patterns. These observations show that Ca-based BMGs are subjected to multiple brittle fracture modes under compressive loading. Periodic nanoscale corrugations were found in the hackle region, which may indicate local plasticity for the brittle fracture.     

Stabilization of Arsenic- and Barium-Rich Glass Manufacturing Waste

Effective solidification∕stabilization (S∕S) of arsenic- and barium-containing D004∕D005 waste was accomplished by using a binder of cement with 40% class C fly ash and either ferrous sulfate or ferric sulfate as an additive. Addition of iron salts improves arsenic solidification∕stabilization (S∕S). Barium may be encapsulated within the stabilized matrix as barium sulfate. Recommended mole ratios for iron∕arsenic and barium∕sulfate are at least 6 and 1.2, respectively. A binder∕waste ratio of 0.15 is volume efficient, but the mix design must be carefully controlled to achieve adequate S∕S. In practice, the heterogeneity of waste and large-scale mix operations may preclude close control of reagent dosages, so a binder∕waste ratio of 0.40 is preferable. Ferrous sulfate additive is preferable for arsenic S∕S because it is effective over a wider range of mix designs and over a long-term curing period. Toxicity characteristic leaching procedure results degraded with long curing time for some mix designs with ferric sulfate additive.     

Measurement of Solute Diffusion Behavior in Fractured Waste Glass Media

Determination of aqueous diffusion coefficients of solutes through fractured media is essential for understanding and modeling contaminant transport at many hazardous waste disposal sites. Development of experimental methods and measurements for the characterization of diffusion in fractured glass media is necessary for the design and performance assessment of glassified radionuclear waste disposal facilities. We report on the use of time-lag diffusion experimental method to assess the diffusion behavior of three different solutes (Cs, Sr, and pentafluoro benzoic acid) in fractured, immobilized low activity waste (ILAW) glass forms. A fractured media time-lag diffusion experimental apparatus, which allows the measurement of diffusion coefficients, has been designed and built for this purpose. Use of time-lag diffusion method, a considerably easier experimental method than the other available methods, was not previously demonstrated for measuring diffusion in fractured waste glass media. Hydraulic conductivity, porosity, and diffusion coefficients of a solute were experimentally measured in fractured glass blocks using this method for the first time. Results agree with the range of properties reported for similar rock media earlier, indicating that the time-lag experimental method can effectively characterize the diffusion coefficients of fractured ILAW glass media. Data presented are rare and useful for the design of vitrified glass disposal facilities.     

Fatigue and Fracture Behavior of a Ca-Based Bulk-Metallic Glass

The compression and fatigue behavior of a Ca₆₅Mg₁₅Zn₂₀ bulk-metallic glass (BMG) was studied in air at room temperature. During the preparation of cubical samples of the Ca₆₅Mg₁₅Zn₂₀ for compression and fatigue investigations, small spherical cavities were found. Under both monotonic and cyclic compression loadings of the samples, fractures initiated at these cavities and propagated in a direction generally parallel to the loading axis. Finite-element analysis (FEA) was used to model the fracture behavior. The FEA of a centrally located spherical void showed that under compression loading, large tensile stresses evolved in the cavities. The orientation of the maximum principal stress (P1) was found to be normal to the direction of crack propagation, which is consistent with the experimental finding. Stresses in deeply embedded adjacent voids and those in superficial voids were also studied. The influence of the void location in the cubical sample on the fracture behavior was quantitatively discussed.     

Linear Elastic Fracture Mechanics Pullout Analyses of Headed Anchors in Stressed Concrete

The results of research initiated in the early 1980s led to the replacement of plasticity-based design guidelines for the load-carrying capacity of headed anchors embedded in concrete with those developed using fracture mechanics. While provisions are available in the design codes that account for the presence of tensile fields causing concrete cracking, no provisions are available for anchors embedded in prestressed concrete. This paper presents the results of linear elastic fracture mechanics (LEFM) analyses and of a preliminary experimental investigation of the progressive failure of headed anchors embedded in a concrete matrix under compressive or tensile prestress. The model predicts an increase (decrease) in load-carrying capacity and ductility with increasing compressive (tensile) prestress. It is shown that despite neglecting the dependence on size of concrete fracture toughness, LEFM predicts with remarkable accuracy the functional dependence of the ultimate capacity on prestress.     

应用废铬钴催化剂为原料生产陶瓷、玻璃色料的研究探讨

对氟化工艺废铬钴催化剂回收利用进行了研究,分析了废铬钴催化剂的主要成分.探讨了利用废铬钴催化剂开发陶瓷、玻璃高温色料的方法.通过一系列的试验,得到了陶瓷、玻璃高温黑色色料,此色料加入坯料中打板烧成,发色稳定,着色力强.     

实验室废弃玻璃作为一种化学试剂在火试金分析中的应用

本文充分调查了废弃玻璃的回收与利用情况,以实验室废弃玻璃的性质为基础,提出了将实验室废弃玻璃应用到分析铅阳极泥和铅精矿中金、银含量的观点,并进行了相关的试验研究,实验样品包括铅阳极泥和铅精矿。通过对实验结果的分析,确定了实验室废弃玻璃替代二氧化硅作为一种化学试剂用于铅阳极泥和铅精矿中金、银含量的试剂用量,保证了分析结果的准确性满足标准方法所规定的精密度要求范围。     

Fracture Mechanics Model for Analysis of Plain and Reinforced High-Performance Concrete Beams

In developing a one-dimensional analysis and design procedure for reinforced concrete structures, research is generally based on yield phenomena and the plastic flow of steel in tension and concrete in compression. The ability of concrete to resist tension is considered in the form of tension stiffening or is completely disregarded. This procedure does not account for the influence of structural size in changing the failure mode and the stress distribution across the uncracked or cracked ligament. The key factor affecting this stress distribution is found to be the strain-softening modulus. This paper presents an improved model that is based on the fundamental equilibrium equation for the progressive failure of plain concrete beams. The concrete stress-strain relationship in tension is derived by calculating the peak tensile stress and softening modulus for different depths of beams on the basis of the fracture parameters obtained with the size effect law. Thus, the proposed model uses the peak tensile stress and the softening modulus, which vary depending on the size of the beam. To study the effect of the strength of high-performance concrete (HPC) on the concrete tensile stress-strain relationship, the experimental load-deflection plots of different-sized beams are compared with those obtained by using the proposed analytical model for eight different mixes made with locally available fly ash and slag. The model is also extended for lightly reinforced concrete beams, and the results are compared with those in the literature and are found to be in good agreement.     

Effect of Clay Slime on the Froth Stability and Flotation Performance of Bastnaesite with Different Particle Sizes

Russian Journal of Non-Ferrous Metals - To investigate the effect of kaolin particles on the flotation performance and froth stability of different particle sizes of bastnaesite, batch flotation...     

宿主石墨粒径对FeCl_3-NiCl_2-GICs的微波吸收性能的影响

以不同粒径的天然鳞片石墨为原料,通过调节反应参数分别制备出一阶的三元FeCl_3-NiCl_2-GICs,系统考察了石墨粒径对FeCl_3-NiCl_2-GICs的导电性能和微波吸收性能的影响。结果表明:FeCl_3-NiCl_2-GICs是一种介电损耗型微波吸收材料,粒径为165μm的一阶FeCl_3-NiCl_2-GICs的最大反射损耗量最大,高达-10.3 d B。在低频范围内,粒径为74μm的FeCl_3-NiCl_2-GICs的吸波性能最好。