Showing papers on "Crack closure published in 2004"
TL;DR: An overview of the virtual crack closure technique is presented, the approach used is discussed, the history summarized, and insight into its applications provided.
Abstract: : An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.
1,354 citations
TL;DR: In this paper, generalized crack initiation and crack damage thresholds of rock masses are proposed, where the crack initiation threshold is defined by σ1−σ3=A σcm and the crack damage threshold is determined by π 1−σ 3=B σ cm for jointed rock masses, where B is the uniaxial compressive strength of the rock masses and A is the material constant.
624 citations
TL;DR: In this article, the authors consider fracture swarm formation in sedimentary rock and identify three regimes of fracture spacing according to the magnitude of the subcritical index of the fracturing material, and use a subcritical crack-propagation rule, where propagation velocity during stable growth scales with the cracktip stress intensity factor.
Abstract: Abstract Swarms or clusters represent an exception to the widely accepted idea that fracture spacing in sedimentary rock should be proportional to mechanical layer thickness. Experimental studies and static stress analysis do not provide adequate explanation for fracture swarm occurrence. The problem is re-examined numerically, accounting for the dynamics of pattern development for large populations of layer-confined fractures. Two crucial aspects of this model are: (1) the inclusion of three-dimensional effects in calculating mechanical interaction between simultaneously propagting fractures; and (2) the use of a subcritical crack-propagation rule, where propagation velocity during stable growth scales with the crack-tip stress intensity factor. Three regimes of fracture spacing are identified according to the magnitude of the subcritical index of the fracturing material. For low subcritical index material (n = 5) numerous fractures propagate simultaneously throughout a body resulting in irregular spacing that is, on average, much less than layer thickness. For intermediate subcritical index (n = 20) one fracture propagates at a time, fully developing its stress shadow and resulting in a pattern with regular spacing proportional to layer thickness. For high subcritical index cases (n = 80) fractures propagate in a fashion analogous to a process zone, leaving a fracture pattern consisting of widely spaced fracture clusters.
282 citations
TL;DR: In this article, the authors investigated the fracture and damage mechanisms of rock induced by the accumulation of microcracks by moment tensor analysis, as well as by the moving point regression technique, both of which were applied to acoustic emission (AE) and strain data obtained from triaxial compression tests.
262 citations
TL;DR: The state-of-the-art in finite element analysis for plasticity-induced fatigue crack closure can be found in this article, where a comprehensive overview is presented, summarizing issues which must be considered and emphasizing potential difficulties.
200 citations
25 Nov 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a convergent lens is used to deliver 1.2-J, 8-ns laser pulses by a Q-switch Nd:YAG laser, operating at 10-Hz.
Abstract: Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 1.2 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto a water-immersed type aluminum samples. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the higher the pulse density the larger the zone size with compressive residual stress. Densities of 900, 1350 and 2500 pulses/cm 2 with infrared (1064 nm) radiation are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. Fatigue crack growth rate is compared in specimens with and without LSP process. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness in the 6061-T6 aluminum alloy.
197 citations
TL;DR: In this paper, displacement-controlled peeling of a flexible plate from an incision-patterned thin adhesive elastic layer was investigated. And the authors found that crack initiation from a single incision on the film occurs at a load much higher than that required to propagate it on a smooth adhesive surface; multiple incisions thus cause the crack to propagate intermittently.
Abstract: Inspired by the observation that many naturally occurring adhesives arise as texturedthin films, we consider the displacement-controlled peeling of a flexible plate from an incision-patterned thin adhesive elastic layer. We find that crack initiation from an incision on the film occurs at a load much higher than that required to propagate it on a smooth adhesive surface; multiple incisions thus cause the crack to propagate intermittently. Microscopically, this mode of crack initiation and propagation in geometrically confined thin adhesive films is related to the nucleation of cavitation bubbles behind the incision which must grow and coalesce before a viable crack propagates. Our theoretical analysis allows us to rationalize these experimental observations qualitatively and quantitatively and suggests a simple design criterion for increasing the interfacial fracture toughness of adhesive films.
185 citations
TL;DR: In this paper, the authors proposed a new method for evaluating the structural or geometric stress in welded constructions based on the computed stress value 1-mm below the surface in the direction corresponding to the expected crack path.
181 citations
TL;DR: In this article, a study was conducted to examine the recently proposed fatigue crack driving force parameter, K ∗ =K max α ( Δ K + ) (1−α), and its ability to predict the crack growth rate for different R-ratios.
177 citations
TL;DR: In this article, the relationship between FCP rate and stress intensity factor range for large cracks consisted of two sections with different slopes due to the transition of the operative micromechanisms of fracture.
173 citations
TL;DR: In this paper, the energy of the solid can be computed from standard infinitesimal deformation theory and the opening of the crack faces creates a capacitive gap that can store electrical energy.
TL;DR: In this paper, a high-resolution phase contrast imaging technique has been used for the reconstruction of clear crack images together with the details of microstructural features, and its feasibility is confirmed.
TL;DR: In this paper, the micro-mechanisms of fatigue crack nucleation and growth in a commercial high-pressure die cast automotive AZ91E-T4 Mg component were revealed.
TL;DR: A detailed analysis of crack propagation in tetragonal zirconia polycrystals doped with 3 mol% of Y2O3 (3Y-TZP) ceramics is presented in this paper.
Abstract: A detailed analysis of crack propagation in tetragonal zirconia polycrystals doped with 3 mol% of Y2O3 (3Y-TZP) ceramics is presented. Crack propagation tests have been conducted for crack velocities of 10-12-10-3 m/s in several environments, including air, water (in the temperature range of 3°-85°C), secondary vacuum (10-5 mbar), and silicon oil. Analysis of the experimental results-three propagating regimes that are dependent on the environment and a marked threshold below which no propagation occurs-shows that stress corrosion by water molecules is the key mechanism for crack propagation. The effect of grain size on the crack velocity is quantified and analyzed in terms of transformation toughening. Experiments under cyclic loading have been conducted to quantify the effects of cyclic fatigue. Crack velocities are higher under cyclic loading than that predicted by stress corrosion alone, and the threshold is lower. Experiments that have been conducted at two different frequencies (0.1 and 1 Hz) and static-fatigue/cyclic-fatigue sequences show that both stress corrosion by water and pure cyclic-fatigue effects are operative under alternative stresses.
TL;DR: Post hoc analyses of data from previously tested bovine and antler cortical bone compact specimens demonstrates that, in contrast to crack initiation approach, the crack propagation approach successfully identifies the superior toughness properties of red deer's antlers cortical bone.
TL;DR: In this paper, the dynamic fracture process analysis for different waveforms of borehole pressure was conducted using a proposed numerical simulation method in order to verify the dynamical fracture mechanism related to blast-induced borehole breakdown.
TL;DR: In this article, the results of fatigue crack growth tests performed on welded ferritic steel plates are reported, and it can be observed that the technique is sensitive to the effects of crack closure and the presence of tensile and compressive residual stresses due to welding.
Abstract: Thermoelastic stress analysis has been developed in recent years as a direct method of investigating the crack tip stresses in a structure under cyclic loading. This is a consequence of the fact that stress intensity factors obtained from thermoelastic experiments are determined from the cyclic stress field ahead of a fatigue crack, rather than inferred from measurement of the crack length and load range. In the present paper the results of fatigue crack growth tests performed on welded ferritic steel plates are reported. From the results it can be observed that the technique is sensitive to the effects of crack closure and the presence of tensile and compressive residual stresses due to welding.
TL;DR: In this article, the authors presented a plane solution for the stresses and electric fields in an infinite body around a cylindrical cavity with an elliptical cross-section, where the electric field from the interior of the cavity was used in conjunction with the energy change formula to calculate the total energy release rate per crack tip when a Griffith crack propagates.
TL;DR: In this paper, an experimental backtracking technique and finite element analysis have been employed to evaluate the stress intensities along the front of an elliptical surface crack in a cylindrical rod.
Abstract: Experimental backtracking technique and finite element analysis have been employed to evaluate the stress intensities along the front of an elliptical surface crack in a cylindrical rod. The finite element solution covers a wide range of crack shapes loaded under end-free and end-constrained axial tension and pure bending. Convenient closed form stress intensity expressions along the whole crack front for each of the loading cases have been given in terms of the crack aspect ratio, crack depth ratio and place ratio. The closed form solutions have been compared against a number of representative solutions collected from the literature. It has been found that different finite element results for the interior points are generally in good mutual agreement, while solutions derived from other methods may sometimes indicate different trends. At the surface interception point agreement is less good because of a complication in the interpretation of stress intensity there. Experimental backtracking results on the end-constrained axial tension case corroborate well with the closed form solution presented. It suggests that the current closed form solution is adequate in describing the stress intensities along the whole crack front of real surface cracks in cylindrical rods.
TL;DR: In this paper, the authors developed a Stroh-type formalism for antiplane deformation and then investigated the fracture mechanics for an elliptical cavity in a magnetoelectroelastic solid under remotely uniform in-plane electromagnetic and/or anti-plane mechanical loading, which allowed them to take the electromagnetic field inside the cavity into account.
TL;DR: In this paper, the authors deal with the fatigue crack growth in a carbon black filled cis-1,4-polyisoprene rubber under relaxing loading conditions, and they focus on the determination of the scenario of crack growth.
Abstract: The present paper deals with the fatigue crack growth in a carbon black filled cis-1,4-polyisoprene rubber under relaxing loading conditions. The study focuses on the determination of the scenario of crack growth. For this purpose, an original “microcutting” method is employed to observe microscopic phenomena involved in the growth of the crack with a SEM. It reveals that the cavitation induced by the decohesion between zinc oxides and rubber matrix is the major fatigue damage and that the crack tip is composed of stretched elliptical areas surrounded by highly stretched and crystallized ligaments. Finally, the observations are considered to establish the fatigue crack growth mechanism.
TL;DR: In this article, the fatigue properties of two types of cold-work tool steels tempered at various temperatures were evaluated and the microstructure and fracture surface morphology were correlated to the fatigue behavior.
Abstract: The fatigue properties of two types of cold-work tool steels tempered at various temperatures were evaluated. The microstructure and fracture surface morphology were correlated to the fatigue behavior. Cold-work tool steels using this study were a conventional tool steel (JIS SKD11; 1.4C-11Cr-0.8Mo-0.2V) and its modified steel (M-SKD11; 0.8C-8Cr-2Mo-0.5V). The fatigue strength of the M-SKD11 steel increased 20 pct over that of the SKD11 steel for any number of cycles. This is attributed to the refinement of primary M7C3 carbides. These M7C3 carbides fractured during fatigue and were found at the sites of fatigue crack initiation. Change in crack initiation behavior was confirmed by acoustic emission testing. The S-N curves of the steels are similar to those of most structural steels. However, the subsurface fatigue crack initiation was dominant at lower alternating stresses. This study points to a general approach of carbide refinement that can be used for the enhancement of fatigue properties.
25 Nov 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of Fe-content on the fatigue damage evolution in a cast A356-T6 alloy was investigated both experimentally and through micro-scale finite element simulations.
Abstract: The effect of Fe-content on the fatigue damage evolution in a cast A356–T6 alloy was investigated both experimentally and through microscale finite element simulations. High cycle fatigue tests indicated that iron content has little influence on the fatigue life in the short lifetime regime ( 106 cycles). At high applied stress levels in the short lifetime regime, fatigue life is dominated by the crack propagation stage. The large plate-like Fe-rich intermetallic particles in high Fe-content castings were observed metallographically to retard the growth of small cracks through crack branching and meandering. For the long lifetime regime, the crack initiation stage is important. Fracture surface examination and finite element analysis revealed that in the absence of other defects such as porosity or oxide films, the large plate-like Fe-rich intermetallic particles in high Fe-content castings promote crack initiation by raising the stress-strain concentration in the eutectic region. Based on experimental observations and finite element analysis, a microstructure-based model was developed involving crack initiation and propagation, which allows quantitative assessment of the influence of Fe-content on the fatigue life. Good agreement was obtained between the model and experimental results.
TL;DR: In this paper, an improved method based on the first-order shear deformable plate theory is developed to calculate the energy release rate and stress intensity factor for a crack at the interface of a bi-layer structure.
Abstract: An improved method based on the first-order shear deformable plate theory is developed to calculate the energy release rate and stress intensity factor for a crack at the interface of a bi-layer structure. By modeling the uncracked region of the structure as two separate Reissner–Mindlin plates bonded perfectly along the interface, this method is able not only to take into account the shear deformation in the cracked region, but also to capture the shear deformation in the uncracked region of the structure. A closed form solution of energy release rate and mode decomposition at the interface crack is obtained for a general loading condition, and it indicates that the energy release rate and stress intensity factor are determined by two independent loading parameters. Compared to the approach based on the classical plate theory, the proposed method provides a more accurate prediction of energy release rate as well as mode decomposition. The computational procedures introduced are relatively straightforward, and the closed form solution can be used to predict crack growth along the layered structures.
TL;DR: In this article, Fatigue crack growth experiments were carried out on sheet specimens of the Russian alloy D16Cz (Al-Cu-Mg alloy) and constant-amplitude tests were performed at different stress ratios.
TL;DR: In this article, an elastic deformable crack tip model is presented for the first time which can improve the split beam solution and is in excellent agreement with analytical 2-D continuum solutions and finite element analyses.
TL;DR: In this article, a unified approach was developed to consider interplay of these two governing forces, Δ K and K max, as fundamental to fatigue, since K max is the governing parameter for these effects.
TL;DR: In this paper, the R-curves, process zones, and shielding stresses of barium titanate (BaTiO3) and partially stabilized zirconia (PSZ) have been studied using compact-tension (CT) specimens.
Abstract: R-curves, process zones, and shielding stresses of barium titanate (BaTiO3) and partially stabilized zirconia (PSZ) have been studied using compact-tension (CT) specimens. BaTiO3 and PSZ exhibited pronounced R-curves that rose over similar crack lengths and showed steady-state toughnesses of 0.7 and 6.4 MPa·m1/2, respectively. Both steady-state toughnesses were ∼80% larger than the initial fracture toughnesses. Ferroelastic domain switching was the main toughening mechanism in BaTiO3, whereas, in PSZ, transformation toughening was the main toughening mechanism. The crack process zone and crack-opening-displacement (COD) profile of each material was studied in detail using atomic force microscopy. Crack-closure-stress distributions were extracted from the COD profiles, using weight-function methods. The resulting stress profiles indicated that compressive residual stresses of 40 MPa in BaTiO3 and 400 MPa in PSZ acted in a limited region behind the crack tip. In the PSZ, crack bridging seemed to be a competing mechanism to transformation toughening.
TL;DR: In this article, an improvement in the methodology for monitoring fatigue crack growth and inferring the stress intensity factor from thermoelastic data is presented, based on a multipoint over-deterministic method (MPODM).
TL;DR: In this article, the effect of crack opening on the ability of chloride ions to diffuse along a crack was investigated and it was found that crack opening significantly influences the ability to diffuse chloride ions along the crack path.