Crack Stability Analysis Research Articles

Effect of Short Fiber Reinforcements on Fracture Performance of Cement-Based Materials: A Systematic Review Approach.

Fracture characteristics were used to effectively evaluate the performance of fiber-reinforced cementitious composites. The fracture parameters provided the basis for crack stability analysis, service performance, safety evaluation, and protection. Much research has been carried out in the proposed study field over the previous two decades. Therefore, it was required to analyze the research trend from the available bibliometric data. In this study, the scientometric analysis and science mapping techniques were performed along with a comprehensive discussion to identify the relevant publication field, highly used keywords, most active authors, most cited articles, and regions with largest impact on the field of fracture properties of cement-based materials (CBMs). Furthermore, the characteristic of various fibers such as steel, polymeric, inorganic, and carbon fibers are discussed, and the factors affecting the fracture properties of fiber-reinforced CBMs (FRCBMs) are reviewed. In addition, future gaps are identified. The graphical representation based on the scientometric review could be helpful for research scholars from different countries in developing research cooperation, creating joint ventures, and exchanging innovative technologies and ideas.

A general property-structure relationship from crack stability analysis on hybrid staggered composites with elasto-plastic matrices

In the present study, fracture analysis is carried out on the representative unit cell of staggered composites consisting of hybrid reinforcements and elasto-plastic matrices. The deformation and failure of hybrid composites are examined through energy-based fracture theory. Analytical formulae for characteristic overlap length, failure strain, and toughness of the unit cell that are related to the properties and geometries of constituents emerge from rigorous derivations. The influences of the matrix plasticity and tablet dissimilarity on the crack stability, the characteristic overlap length, the final failure strain, and toughness are also elucidated. Our study shows that if designed appropriately, the matrix plasticity can effectively improve the material ductility and toughness through crack stabilization. On the other hand, although hybrid reinforcements could effectively tune the ductility, they may cause a loss of material toughness in some cases. More importantly, our model provides guidance to the promising design space where the well-known ductility-strength trade-off dilemma for traditional engineering materials could be resolved.

The edge-notched clamped beam bend specimen as a fracture toughness test geometry

Edge-notched clamped beam bend fracture specimens provide the required geometric stability for controlled crack growth in brittle materials, enabling the measurement of R-curves and cyclic crack growth. In this paper, finite element simulations were carried out on this test geometry to extract the normalized stress intensity factor KI solutions for different useful specimen dimensions, loading tip radius and loads. Based on these results, geometric factors have been proposed that can fit various beam aspect and crack depth ratios. Crack stability analysis is carried out in terms of the R locus for various beam aspect ratios for the clamped beam geometry and compared to other fracture toughness tests. Experimental verification of the same has been carried out at the macro-scale using poly-methyl methacrylate (PMMA) and WC-Co as model materials.

Cause and Stability Analysis of Cracks in Concrete Slab of Rockfill Dam under High Temperature Difference Condition

The causes of cracks in concrete slab from the aspects of structural stress and nonstructural stress are summarized firstly. And then, based on the relationship between the stress intensity factor and the fracture toughness, a 3D finite element model of a concrete face rock fill dam, with concrete slab under partial cracking, is established to study effects of rockfill body deformation, water level and temperature change on the stress distribution. On the basis, the stability and expansion trend of a typical crack are evaluated by numerical simulation of different sizes in depth, especially the influence of the cold-air outbreak.

Unified formulae for evaluating load reduction by change in stiffness of circumferential crack considering general piping systems

The conservatism of leak-before-break (LBB) analysis depends on the methodologies for evaluation of the crack opening displacement (COD) and crack stability analysis, in which the applied load at the cracked section is an important variable. In current procedure, the applied loads are obtained from an uncracked pipe analysis, and the effect of restraint is not assumed in the calculations of COD and the allowable applied moment. When the presence of a crack and the pipe restraint are considered, however, the applied load can be reduced because of the change in the piping system stiffness. In this regard, there have been several proposed analytical expressions to evaluate the restraint effects on COD or crack stability analysis, but the expressions cannot be applied to practical cases because of the limitation of the pipe geometries and applied loading conditions. This study develops unified formulae to evaluate the effective applied loads that enable balanced analyses of both the COD and stability of circumferential cracked pipes. The formulae were developed for a piping system containing a circumferential crack based on the compliance approach. By comparing this with finite element analysis results, the validity of the formulae was demonstrated. It is expected that the proposed formulae can be used as a simple approach to detailed LBB analysis to secure the safety margin before implementing the complex non-linear finite element analysis.

Slow crack growth, its modeling and crack-layer approach: A review

A review of empirical equations for slow crack growth under fatigue and creep conditions is presented. The crack propagation rate is commonly expressed as a function of stress intensity factor or energy release rate. A concept of crack driving force and crack stability analysis is employed to predict crack behavior under different loading conditions; the concept of crack growth resistance, such as an effective surface energy, is used. It is shown that for a stable crack propagation (the energy release rate is a decreasing function of crack length) crack growth equation results from the crack equilibrium condition, if the crack resistance is assumed to be constant. Experimental studies demonstrate that crack growth resistance is not constant, but changes with crack propagation. Formation of the so-called process zone appears to be responsible for the changes. Process zone (PZ) is a material reaction to stress concentration at crack tip and it is commonly observed under fatigue and creep conditions in most engineering materials. For an unstable crack growth (the energy release rate is an increasing function of crack length) the effect of PZ even more dramatic; for example, in a perfectly homogeneous elastic solid slow crack growth would be impossible without the stabilizing effect of PZ. A system of a crack and PZ is referred to as crack-layer (CL). CL driving forces that are thermodynamic forces associated with crack and PZ growth are introduced. CL growth equations are employed to explain the observed variations of crack growth resistance commonly known as R-curve behavior. The evolution of the process zone in a complex stress field is illustrated by an experiment demonstrating how process zone accelerates and decelerates crack growth. Modeling of the crack–process zone interaction is a challenging problem; recent advances in computational techniques make it solvable. The CL approach is illustrated on an example of engineering thermoplastics. Applications to lifetime prediction of structural components, as well as toughness and durability of materials are discussed.

Effect Analysis of Gurson Model Parameters on Crack Extension of Pipeline

Leakage-before-break technique is widely used in high energy pipeline of nuclear plant, for which crack stability of pipeline under complex loading condition is a key issue, and crack growth resistance curve of pipeline material is the important foundation for crack stability analysis. In this paper, ferritic steel A533B is studied, Gurson damage model is used to simulate crack process of contact tension specimen under unitension, and effect of Gurson model parameter on simulation result is discussed. The following results are found during simulation: initial porosity factor is the main parameter, when it increases gradually, unstable crack extension will be observed; however, only initial J toughness is affected by critical porosity factor; the minor parameter is load step control, when it increases, stable and convergent result is obtained. All results in this paper can be used to determine parameters in Gurson mode, which will be foundation for crack extension analysis of pipeline.

Stability Analysis of Cracks in the Stress-Release Boot of Solid Rocket Motor Grain with J-Integral

The stress-release boot is always used in the fore and rear of SRM grain to relief stress-strain concentration under thermal loading. Since the debonded crack in the stress-release boot may be propagation unstable when the internal pressure entered the debonded crack cavity, the SRM with debonded cracks is very dangerous when it is lunched. So the stability analysis of the debonded cracks is very important to evaluate the defect grain structure integrity. In order to investigate the stability of debonded cracks in the stress-release boot of SRM grain during ignition pressurization, three-dimension (3-D) viscoelastic finite element models of the SRM grain with debonded cracks are established. The 3-D singular crack elements at the tips of cracks are developed to simulate the stress-release boot debonded crack propagation. And all the singular crack elements are included in the 3-D J-integral loop surface to improve the calculation precision. Along with the debonded crack propagation, the 3-D J-integrals of the debonded crack tips are respectively calculated to prejudge its expanding trend. The results show that the most dangerous situation will occur in the fore stress-release boot debonded cracks during the rocket being launched.

유효탄성계수를 이용한 균열 비선형 및 재료 비선형을 고려한 파단전누설(LBB) 평가 방법

최근 열출력이 향상된 신규 원자력발전소의 개발이 증가하고 있으며 배관계에 가해지는 모멘트 및 하중의 크기도 증가하는 경향이므로 배관의 파단전누설(LBB) 적용조건 여유도가 작아질 수 있다. 본 논문에서는 이러한 배관에서 LBB 적용조건을 만족시키기 위한 추가적인 여유도 확보의 한 방법으로써 균열의 비선형과 재료물성치를 고려하는 방법을 제시하였다. 균열 및 재료의 비선형을 고려하기 위하여 유한요소해석과 보(beam) 이론을 병용하였다. 원자력 배관을 모델로 하여 본 논문에서 제안한 방법으로 LBB 균열안정성 해석을 수행하였으며, LBB 여유도가 낮은 위치에서 균열 및 재료 비선형을 고려함으로써 추가적인 LBB 여유도를 확보할 수 있음을 확인하였다.

Crack-Path Analysis for Brittle and Non-Brittle Cracks: A Cell Method Approach

Defining the crack path in brittle and non- brittle crack is not easy, due to several unknowns. If the direction of crack propagation can be computed by means of one of the existing criteria, it is not known whether this direction will remain constant during crack propagation. A crack initiation leads to an enhanced stress field at crack tip. During propagation, the en- hanced tip stress field propagates into the solid, locally interacting with the pre-existing stress field. This inter- action can lead to modifications of the propagation di- rection, depending on the domain and crack geometry. Moreover, trajectory deviation affects the length of crack propagation. Thus, the length of crack propagation too depends on the domain and crack geometry. Finally, the local interaction between stress fields of opposite signs can return a modified condition of crack arrest. Crack stability analysis cannot be performed without consider- ing this interaction. The problem of defining trajectory deviation,propagationlengthand crack stabilizationisof particular interest in brittlecracks, since these cracks de- velopstaticallyfrom themoment ofcrack initiationforth. It will be shown here how a numerical code for use with the CM returns an accurate crack path for brittleand non- brittle cracks. In both cases, the stress analysis has been performed on the plane of Mohr for each step of the car- rying process. At crack propagation, an automatic tool of nodal relaxation with remeshing is used to update the domain geometry. keyword: Cell Method, automatic remeshing, crack stability,failure mechanism analysis.

Plastic hinges development and crack stability analysis in a circular ring

Abstract The primary purpose of this work is to demonstrate that the location of a crack can strongly affect the sequence of plastic hinge development which in turn affects crack stability of a structure. A specific example of an elastic–plastic ring loaded with diametrically opposite concentrated loads is employed to investigate these effects. The method used is based on elastic superposition to obtain the elastic–plastic behavior and to evaluate the crack stability with plastic hinges present.

Crack-stability analysis and fracture toughness of ceramic bend bars with a modified circular cross section

Previous analysis has shown that the round bend bar is more stable than the rectangular bend beam. The geometry of the round bend bar was slightly modified to permit precracking of ceramic bars for subsequent fracture-toughness testing. Stability solutions of this new modified round bend bar were found as a function of precrack length for several machine-compliance values. A threshold crack length was determined which predicted the transition from unstable to stable fracture behavior. Experiments with silicon nitride and alumina specimens verified the results of the analysis.

Crack stability analysis for rock fracture toughness tests

AbstractA stable crack extension is a precondition for fracture toughness tests using chevron‐notched specimens. The paper analyses the stability problem for crack extension in two chevron‐notched specimens suggested by ISRM. Stability factors are calculated with various compliances of testing machine under different loading conditions. It is pointed out that the loading manner, compliance of the testing machine, as well as the specimen configurations have great influence on crack growth stability.

Stability Analysis Of Cracks Propagating In Three Dimensional Solids

AbstractWe present a theory for the morphology of the fracture surface left behind by slowly propagating cracks in linear, isotropic and homogeneous three dimensional solids. Our results are based on first order perturbation theory of the equations of elasticity for cracks whose shape is slightly perturbed from planar. For cracks propagating under pure type I loading we find that all perturbation modes are linearly stable, from which we can predict the roughness of the fracture surface induced by fluctuations in the material. We compare our results with the classical results for cracks propagating in two dimensional systems, and discuss the effects in the three dimensional analysis which result from taking into account contributions from non-singular terms of the stress field, as well as the effects arising from finite speeds of crack propagation.

The incorporation of earthquake loadings within a crack stability analysis for piping systems

The tearing modulus approach has been used to demonstrate the stability of a circumferential through-wall crack in Type 304 stainless steel in a Boiling Water Nuclear Reactor piping system when the system is subjected to earthquake loadings which produce a displacement-control loading state at the system ends. To date the stability has been demonstrated via a static analysis. However, this paper shows that the same procedure can be used even though dynamic effects, including inertial loadings, are operative.