Influence Of Initial Crack Length Research Articles

Influence of initial crack length on fracture properties of limestone using DIC technique

Due to limitations in equipment and testing methods, there is currently little literature studying the effect of initial crack length (a0) on fracture parameters. Considering that limestone is often associated with the construction of cultural heritage buildings, monuments, tunnels, subways and power stations, so limestone beams were used as the experimental objects, and were used to conduct three-point bending (3-p-b) tests based on digital image correlation (DIC) technique to study the influence of a0 on fracture parameters, including critical crack tip opening displacement (CTODc), nominal strength without considering the crack (σN), nominal strength considering the crack (σn), critical mid-span deflection (δc), critical crack mouth opening displacement (CMODc), unstable fracture toughness (KIcun), fracture energy (Gf) and fully developed fracture process zone length (lmFPZ). In addition, based on the boundary effect model (BEM), the relationships between the crack-to-depth ratio (α0 = a0/D) with KIcun and Gf were analyzed. The findings indicate that, as a0 increases, σN, KIcun, Gf, and lmFPZ decrease gradually, while CMODc, CTODc, and δc increase gradually; as two important parameters of the BEM, the boundary influence length (A1) and size-independent fracture energy (GF) are 27.08 mm and 74.67 N/m, respectively.

Probability of instant rail break induced by wheel–rail impact loading using field test data

ABSTRACT The probability of an instant rail break, initiated at a single pre-existing rail foot crack due to a severe wheel impact loading, is predicted using statistical methods and a time-domain model for the simulation of dynamic vehicle–track interaction. A linear elastic fracture mechanics approach is employed to calculate the stress intensity at the crack in a continuously welded rail subjected to combined bending and temperature loading. Based on long-term field measurements in a wayside wheel load detector, a three-parameter probability distribution of the dynamic wheel load is determined. For a faster numerical assessment of the probability of failure, a thin plate spline regression is implemented to develop a meta-model of the performance function quantifying the stress intensity at the crack. The methodology is demonstrated by investigating the influence of initial crack length, fracture toughness and rail temperature difference on the risk for an instant rail break.

Analysis of the Effect of Initial Crack Length on Concrete Members Using Extended Finite Element Method

The extended failure process of the prefabricated one-side notched three-point bending concrete beam was simulated by the extended finite element method. Combined with the double-K fracture criterion, the influence of the initial crack length on the fracture parameters of the three-point curved concrete beam and the influence of the initial crack on the concrete structure were studied. In addition, the dynamic response state and crack propagation process of Koyna concrete gravity dam under seismic conditions are simulated, and the influence of initial crack length on these factors is studied. The results show that the existence and length of the initial crack have a certain impact on the development of cracks in concrete members. Under the action of earthquake, the stiffness of the concrete gravity dam is reduced, and the response period of the horizontal and vertical displacement of the top of the gravity dam is not significantly correlated with the initial crack length. However, the opening range of the crack increases as the initial crack length increases. When the initial crack length is 0 m, 0.5 m and 1 m, the crack opening upstream of the gravity dam is 1.26 cm, 1.61 cm and 1.86 cm respectively; the downstream crack opening is 1.73 cm, 2.35 cm and 2.53 cm.

Analysis of Fatigue Life and Influence Factors of Tubing with Initial Crack

Three-dimensional stresses are analyzed in the tubing working based on the theory of thick-walled cylinder, and the stress intensity factor expression is derived on longitudinal and circumferential extending cracks in the tubing. Tubing fatigue life is calculated according to given condition through the preparation of the corresponding program. Influence of initial crack length, change of the pressure and the tubing wall thickness on the fatigue life are discussed.

Effect of Geometry Factors on Dynamic Fracture Behavior for Mechanical Heterogeneous Welded Joint

Welded joint is a mechanical heterogeneous body, which is composed of base metal, weld metal and heat affected zone (HAZ). Many welded structures endure dynamic load in service. Mechanical heterogeneity has important influence on dynamic fracture behaviour of welded joint. In the present investigation, dynamic fracture parameter of J-integral of undermatched three-point-bending (TPB) welded joint specimens containing longitudinal crack with different geometry were computed. The strain rate near crack tip reaches 103 under the impact velocity of 5m/s, so dynamic properties under corresponding strain rate should be used in dynamic analysis. The results of instrumented impact experiment were used as the input parameters in the computation. Dynamic J-integral was evaluated using virtual crack extension (VCE) method of MARC finite element code in 3-D condition. Dynamic J-integral evaluated by VCE method is path independent. The value of dynamic J-integral curve increases with loading time smoothly, so inertia force has little influence on dynamic J-integral. The values of dynamic J-integral decrease with increase of weld width. When the weld width is bigger than 5mm the influence of base material on weld metal is not evident. The influence of initial crack length on dynamic J-integral is complicate. The value of dynamic J-integral of the computation model with initial crack length of a/W=1/4 is the highest, and that of the computation model with initial crack length of a/W=1/8 is the lowest. The results are helpful for dynamic fracture evaluation of macro-heterogeneous welded joints.

The Influence of Initial Crack Length on Critical Stress Intensity Factor K1

Abstract It is postulated that initial crack length always affects the critical propagation of a crack, except when absolutely elastic materials are considered. The reason for this statement is explained, and a new fracture mechanics theory is presented and experimentally justified, complementing previous works in which it was partially developed. The main innovation presented in this paper is a new fracture mechanics method, called “Limit Line Replacement,” which is thought to be applicable to any type of structure, provided some experimental verification is made. This basis of the method consists in the acceptance that the critical crack length of a cracked structure subjected to fatigue always can be obtained experimentally, if the maximum and the minimum fatigue loads are known. From this critical crack length, the life of a structure can be estimated experimentally if under similar conditions, the number of required cycles is measured.

Simulation of creep crack growth in ceramic composites

The elevated temperature response resulting from tensile creep of fiber reinforced ceramic composites was modeled using Monte Carlo simulation. The model consisted of a uniaxially loaded fiber tow aligned with the direction of applied load, and modeled the growth of matrix cracks resulting from creep failure of bridging fibers. A creep strain rate consisting of primary and steady state components was assumed, and each component was modeled by a power law relationship. Power law creep exponents in the range of 2.0–2.5 for a selected SiC/SiC system at stress levels ranging from 60 MPa to 200 MPa were evaluated. Fatigue-like behavior was predicted as a result of tensile creep, and a fatigue exponent of 3.03 ± 0.07 was predicted for nominal stress levels less than 200 GPa. The influence of initial crack length on failure lifetime was also studied, but was found to have little influence on the predicted lifetime. The predicted failure response suggested a stress dependent creep process could be used to model experimental data and evaluate the failure mechanism of reinforced composites.

複合材料の疲労寿命推定法 引張モードを基にした場合

In this paper, a fatigue life prediction method based on linear fracture mechanics is proposed to composite materials. In order to evaluate this method, the cyclic loading tests of graphite/epoxy composites plates with [±30]s, [±45]s and [±60]s laminate orientations were carried out.It was revealed that the computational result was satisfactory agreement with the experimental ones except long life region [±30]s laminate orientations. The fracture mode was the combination of tension and shear modes when the angle between loading direction and fiber orientation became small. Therefore, it is recognized that the long life prediction of these materials has to require fracture mechanics base on the combined mode which is not dealt with in this paper.Furthermore, the effects of material properties on fatigue life were investigated as an application of the proposed model to material design. As a result, it became clear that the fatigue life is affected by the ultimate tensile and shear strengths of the matrix and depends strongly on the influence of initial crack length that is calculated from the size of voids or defects.