Crack Growth Data Research Articles

Multiaxial fatigue and life prediction of elastomeric components

Elastomeric components have wide usage in many industries. The typical service loading for most of these components is variable amplitude and multiaxial. In this study a general methodology for life prediction of elastomeric components under these typical loading conditions was developed and illustrated for a passenger vehicle cradle mount. Crack initiation life prediction was performed using different damage criteria. The methodology was validated with component testing under different loading conditions including constant and variable amplitude in-phase and out-of-phase axial–torsion experiments. The optimum method for crack initiation life prediction for complex multiaxial variable amplitude loading was found to be a critical plane approach based on maximum normal strain plane and damage quantification by cracking energy density on that plane. Rainflow cycle counting method and Miner’s linear damage rule were used for predicting fatigue life under variable amplitude loadings. The fracture mechanics approach was used for total fatigue life prediction of the component based on specimen crack growth data and FE simulation results. Total fatigue life prediction results showed good agreement with experiments for all of the loading conditions considered.

Prediction of Fatigue Crack Growth of 2024-T351 by Grey <i>GM</i>(1,1) Model with Rolling Check

The study is focused on the investigations into applying the grey model with rolling check to the prediction of fatigue crack growth. Fatigue crack growth data of compact tension specimens made of 2024-T351 aluminum-alloy plate tested under constant-amplitude loads were carried out for verifications. The optimal values of parameter affecting the accuracy of prediction were found by variational analysis. Using four experimental crack lengths as the source series and the optimal value of parameter for modelling with rolling check, it was found almost entire fatigue crack growth curve of the specimen can be predicted accurately. Besides, the analyzed results including number of rolling check performed, loading cycle corresponding to the maximum predicted crack length, fractured cycle of specimen, cycle ratio of loading cycle and fractured cycle, and percentage of error between maximum predicted and experimental crack length for all specimens were tabulated.

Derivation of Effective Strain-Life Data, Crack Closure Parameters and Effective Crack Growth Data from Smooth Specimen Fatigue Tests

Derivation of Effective Strain-Life Data, Crack Closure Parameters and Effective Crack Growth Data from Smooth Specimen Fatigue Tests

Fatigue crack growth modeling of attachment lugs

In the present paper, computational procedures for the strength analysis of two cracked lug configurations are proposed. The authors consider the lug with single through-the-thickness crack as well as with single quarter-elliptical corner crack. The stress analysis and the fatigue life evaluations are tackled for both configurations. Numerical approaches based on quarter-point (Q-P) singular finite elements are developed for stress intensity factor calculations. Furthermore, the finite element analysis is applied in order to evaluate the polynomial expression for the stress intensity factor calculation of the lug with one through-the-thickness crack. The residual life estimation of cracked lugs is analyzed by employing the crack growth law based on a two-parameter driving force model. Moreover, the crack growth path for the lug with quarter-elliptical crack is simulated. The reliability of the proposed procedures is verified using experimental fatigue crack growth data. Fatigue life calculations and crack path simulations show a very good agreement with experimental observations.

Strength Prediction in Open Hole Composite Laminates by Using Discrete Damage Modeling

The present paper addresses the issue of direct simulation of complex local failure patterns in laminated composites. A model capable of the discrete modeling of matrix cracking, delamination, and the interaction of these two damage modes is proposed. The analytical technique develops the regularized extended finite element method for the simulation of matrix crack initiation and propagation at initially unknown locations, as well as a cohesive interface model for delamination. The regularized extended finite element method preserves the Gaussian integration schema in each element regardless of the enrichment required to model cracking and is capable of representing the complex kinematics of crack networks in composite laminates. The technique uses independently measured standard ply-level mechanical properties of the unidirectional composite (stiffness, strength, fracture toughness). Failure simulations of composites containing open holes are presented. Although the process of crack initiation is impossible to capture precisely due to local material variations the proposed method exhibits excellent agreement with experimental data for matrix and delamination crack growth in quasi-isotropic open hole graphite-epoxy composites with thick plies, where the composite fails in the delamination failure mode.

Fatigue Crack Growth Analysis Under Spectrum Loading in Various Environmental Conditions

The fatigue process consists, from the engineering point of view, of three stages: crack initiation, fatigue crack growth, and the final failure. It is also known that the fatigue process near notches and cracks is governed by local strains and stresses in the regions of maximum stress and strain concentrations. Therefore, the fatigue crack growth can be considered as a process of successive crack increments, and the fatigue crack initiation and subsequent growth can be modeled as one repetitive process. The assumptions mentioned above were used to derive a fatigue crack growth model based, called later as the UniGrow model, on the analysis of cyclic elastic–plastic stresses–strains near the crack tip. The fatigue crack growth rate was determined by simulating the cyclic stress–strain response in the material volume adjacent to the crack tip and calculating the accumulated fatigue damage in a manner similar to fatigue analysis of stationary notches. The fatigue crack growth driving force was derived on the basis of the stress and strain history at the crack tip and the Smith–Watson–Topper (SWT) fatigue damage parameter, D = σmaxΔe/2. It was subsequently found that the fatigue crack growth was controlled by a two-parameter driving force in the form of a weighted product of the stress intensity range and the maximum stress intensity factor, ΔKpKmax1−p. The effect of the internal (residual) stress induced by the reversed cyclic plasticity has been accounted for and therefore the two-parameter driving force made it possible to predict the effect of the mean stress including the influence of the applied compressive stress, tensile overloads, and variable amplitude spectrum loading. It allows estimating the fatigue life under variable amplitude loading without using crack closure concepts. Several experimental fatigue crack growth datasets obtained for the Al 7075 aluminum alloy were used for the verification of the proposed unified fatigue crack growth model. The method can be also used to predict fatigue crack growth under constant amplitude and spectrum loading in various environmental conditions such as vacuum, air, and corrosive environment providing that appropriate limited constant amplitude fatigue crack growth data obtained in the same environment are available. The proposed methodology is equally suitable for fatigue analysis of smooth, notched, and cracked components.

Environmental Crack Growth Behavior Affected by Thickness/Geometry Constraint

This article gives a short review on the effects of thickness/constraint and environment on crack growth behavior under cyclic and static loadings. Fatigue crack growth data taken from the literature, corresponding to different environments, ranging from vacuum to air and NaCl solution for a number of alloys and different specimens geometries are presented and analyzed. Reported results indicate that for relatively inert material/environment systems, there is a weak thickness/constraint effect on fatigue crack growth behavior. On the other hand, for corrosive material/environment systems, there is a significant thickness/constraint effect on crack growth rate behavior under both cyclic and static loadings. Some implications related to crack growth modeling are suggested.

Fatigue Crack Growth Behavior of Silicon Nitride: Roles of Grain Aspect Ratio and Intergranular Film Composition

The role of microstructure in affecting the fatigue crack growth resistance of grain bridging silicon nitride ceramics doped with rare earth (RE = Y, La, Lu) oxide sintering additives was investigated. Three silicon nitride ceramics were prepared using MgO‐RE2O3 and results were compared with a commercial Al2O3‐Y2O3‐doped material. Decreasing stress intensity range (ΔK) fatigue tests were conducted using compact‐tension specimens to measure steady‐state fatigue crack growth rates. Specimens doped with MgO‐RE2O3 additives showed a significantly higher resistance to crack growth than those with Al2O3‐Y2O3 additives and this difference was attributed to the much higher grain aspect ratio for the MgO‐RE2O3‐doped ceramics. When the crack growth data were normalized with respect to the total contribution of toughening by bridging determined from the monotonically loaded R‐curves, the differences in fatigue resistance were greatly reduced with the data overlapping considerably. Finally, all of the MgO‐RE2O3‐doped silicon nitrides displayed similar steady‐state fatigue crack growth behavior suggesting that they are relatively insensitive to the intergranular film.

An investigation on fatigue crack growth rates through a designed nonsymmetric crack growth test

A nonsymmetric fatigue crack growth (FCG) test is specially designed and performed to study whether FCG test data from nonsymmetric cracking which is unavoidable in practice can be used to determine valid FCG rate information for fatigue life evaluation. Two types of alloys were used in this test and the FCG data were obtained via visual measurements. The effects of boundary conditions and central hole were examined using FEA software and the results showed that within engineering allowable error margin, the theoretical solution of stress intensity factors (SIFs) under the remote uniform tension is valid for nonsymmetric crack in this test. As a result, a method for analyzing the FCG rate of nonsymmetric through-thickness crack is proposed. It is found that the FCG rate parameters in the stable stage have no difference between two crack tips and the crack growth data can be used together to determine the Paris parameters. The proposed method, if supported by further research, can be adopted to validate FCG test data involving nonsymmetric cracking in standard tests.

Effect of Hold Time on Crack Growth Behavior of Pb-Containing and Pb-Free Solders

Four types of loading waveforms were adopted to investigate the effect of hold time on crack growth behavior of Sn-37Pb and Sn-3.0Ag-0.5Cu solders: a sinusoidal waveform, triangular waveform, and trapezoidal waveform with hold times of 1 s, 5 s, and 10 s, and a triangular waveform with hold time of 10 s at maximum tensile load. The experimental results showed that the crack growth behavior of both solders tested under sinusoidal and triangular waveforms without any hold time was predominantly cycle dependent. On the other hand, the crack growth behavior of both solders tested under trapezoidal waveforms with hold times of 1 s, 5 s, and 10 s and triangular waveforms with hold time of 10 s was predominantly time dependent. Under cycle-dependent conditions the crack growth data were a function of J-integral range, while under time-dependent conditions the crack growth data were not a function of the creep J-integral range but rather of the C* parameter.

The interrelation of the parameters in the Paris equation of fatigue crack growth

The majority of the models describing the fatigue crack growth under high cycle fatigue loading has being formulated as the form of Paris equation, da/dN=C(ΔK)n, in which n is a constant and C varies with the load ratio R, as such to interpret the effect of mean stress on the fatigue crack growth behavior of materials. In this paper a modified Walker equation was developed by which the interrelation between C and n, in terms of ratio R, was established. The original equations of Paris’s and Walker’s are the special cases of the new equation. The regression results of the new equation for fatigue crack growth data correlate well with testing results of four kinds of materials.

A unified method of design for fatigue crack growth resistance in structural materials

It is well established that there are two fatigue crack tip driving forces – the cyclic, ΔK, and the static, Kmax. In this study, the effects of each crack tip driving force on crack growth were evaluated for various structural materials. A unified method of design that allows for predicting the response of long and physically small fatigue cracks at positive stress ratios is introduced. Good agreement between predicted and experimental long and physically small fatigue crack growth data was obtained. The importance of this method in material and component design is discussed as part of a contemporary design philosophy.

A three-parameter model for fatigue crack growth data analysis

A three-parameters model for the interpolation of fatigue crack propagation data is proposed. It has been validated by a Literature data set obtained by testing 180 M(T) specimens under three different loading levels. In details, it is highlighted that the results of the analysis carried out by means of the proposed model are more smooth and clear than those obtainable using other methods or models. Also, the parameters of the model have been computed and some peculiarities have been picked out.

A double edge notch specimen design for tension–compression fatigue crack growth testing

Compact, C(T), specimens are commonly used for fatigue and creep-fatigue crack growth testing under constant-load-amplitude conditions. The use of the standard C(T) specimens [ASTM] is limited to positive load ratios. They are also limited in the amount of crack growth data that can be developed at high stress intensity values due to accumulation of plastic and/or creep strains leading to ratcheting in the specimen. Testing under displacement control can potentially address these shortcomings of the load-controlled tests for which the C(T) geometry is unsuitable. A double edge notch tension–compression, DEN(T–C), specimen to perform displacement controlled creep-fatigue crack growth testing is developed and optimized with the help of finite element and boundary element analyses. The specimen has threaded cylindrical ends for applying the loads. The test section is rectangular with a half width, W, and half height, H, and a constant thickness, B. The height to width ratio, H/W, of the specimen must be kept low to avoid buckling during compressive loading while ensuring that the stress-intensity parameter values are not strongly dependent on the chosen H/W value. Simple optimization analysis shows that a H/W ratio of 1.2 is likely to best meet these requirements. However, only performing actual experiments will confirm whether this choice of H/W value is optimum.In the finite element analyses, the specimen is modeled using an effective height (heff) to width (W) ratio, heff/W, of 1.46 to account for the fillet regions on the two ends of the specimens. Accurate expressions for estimating the fracture mechanics crack tip parameters such as the stress intensity parameter, K, the crack mouth opening displacement (CMOD), and the load-line displacement (LLD) are developed over a wide range of crack sizes for the DEN(T–C) specimen. Expressions are also developed for crack size as a function of specimen compliance.

Experimental Study and Numerical Simulation on Fatigue Crack Growth Behavior of GH4133B Superalloy

The fatigue crack growth tests for nickel-based GH4133B superalloy used in turbine disk of a type of aero-engine are carried out at room temperature. The stress intensity factor ranges and the fatigue crack growth rates at various stress ratios are measured, and the corresponding threshold stress intensity factor ranges are determined. Using the Paris formula, the experiment data of fatigue crack growth are analyzed. It is shown that the fatigue crack growth rate increasing with increasing stress intensity factor range and stress ratio, and a modified Paris formula considering threshold stress intensity factor range can describe the fatigue crack growth behavior precisely. The fracture surface morphologies are investigated using a scanning electron microscope. It is shown that in the crack initiation region, steady growth region and rapid growth region, the fracture surface exhibits a cleavage fracture mode, fatigue striations and an intergranular fracture mode, respectively. Finally, the von Mises stresses and stress intensity factors at the crack tip of specimen of GH4133B superalloy at various external loads and crack lengths are simulated using the finite element method, and the threshold stress intensity factors under different maximal external loads at a certain crack length are calculated. The comparison between test and simulation indicates that the stress intensity factors at the crack tip calculated by the finite element method agree well with experimental data.

A study to maximize the crash energy absorption efficiency within the limits of crash space

The design of an engine room is important to protect the passenger from a crash impact by improving the absorption of the crash impact energy. The side member in the engine room absorbs most of the crash impact energy when the vehicle experiences a frontal crash. The side member is of two types: hat and ‘U.’ Analysis of the extent of energy absorption and the mechanism of the side member are necessary through a collapse mode in various load conditions. In this study, the design of experiments was used for evaluating the characteristics of the absorption of crash energy by side members through design variables. First, crash analysis was performed by experiment number extracted from the design of the experiment. Then, using the results of crash analysis, multiple regressions were conducted and sensitivity analysis performed for each design variable. Finally, the optimum design was developed for maximizing the absorption energy per unit weight considering various boundary conditions. In the present study, as a basic step for modeling the fatigue behavior of an extruded Al alloy cylinder, the fatigue crack growth data of the alloy was collected in two orientations. Microstructural analysis revealed that the material had recrystallized grains and clusters of constituent particles aligned in the direction of extrusion. Fatigue life of the samples revealed a shorter fatigue life representing a higher fatigue crack growth rate in the transverse direction.

Effect of Dents on Crack Growth in Aluminum Alloy Under Constant-Amplitude Loading

a0.5in.spherical hardened-steelindenterhead.Dentdepths rangedfrom0.03to0.0325in.,measuredontheconvex side of the specimen. A starter notch of 0.3 in. was produced at the edge of the specimen with a jeweler’s saw blade. The specimen was fatigue-loaded under constant-amplitude loading to produce an initial crack length of 0.37 in., at whichtimereadingsofcracklengthvscyclesbegan.Thesameconstant-amplitudecyclicloadingusedtoproducethe initialcracklengthwasusedduringthetesting.Thecracklengthsweremeasuredwithanopticalmicroscopeat160 magnification. Nine specimens were tested, including three replications for each of the three conditions. Crack growth data are given in both tabular and graphical forms for all specimens. Crack growth rate data are also presented in graphical form. The overall crack growth in the dented specimens was significantly greater than in the pristine specimens. It was also faster, on average, in the reworked specimens; reworking, in general, did not recapture the life displayed by the pristine specimens.

Grey Relational Grade Analysis between Vickers Hardness and Fatigue Crack Growth Data of 2024-T351 Aluminum Alloy

Compact tension specimens cut from 2024-T351 aluminum-alloy plate were used for Vickers hardness tests under low-force scale and then for fatigue crack growth tests under sinusoidal loads, and the scattered data sets obtained including Vickers hardness, initiation cycle and specimen life, exponent m and intercept C of Paris-Erdogan law were collected as a factor set with five factor series for analysis of grey relational grade. Nominal value method was adopted for the preprocess referred to as grey relational generation to obtained new factor series, and then Hsia’s method was used to calculate the grey relational grades among new factor series. The analyzed result named global grey relational grade in matrix form with dimension of shows three main findings: (1) Vickers hardness has the largest influence on specimen life, and vice versa. (2) Vickers hardness, specimen life, and m have a large influence on each other. (3) C has the least influence on any other factors, and vice versa.

Fatigue crack growth due to overloads in plain concrete using scaling laws

Scaling laws are represented in power law form and can be utilized to extract the characteristic properties of a new phenomenon with the help of self-similar solutions. In this work, an attempt has been made to propose a scaling law analytically, for plain concrete when subjected to variable amplitude loading. Due to the application of overload on concrete structures, acceleration in the crack growth process takes place. A closed form expression has been developed to capture the acceleration in crack growth rate in conjunction with the principles of dimensional analysis and self-similarity. The proposed model accounts for parameters such as, the tensile strength, fracture toughness, overload effect and the structural size. Knowing the governed and the governing parameters of the physical problem and by using the concepts of self-similarity, a relationship is obtained between the different parameters involved. The predicted results are compared with experimental crack growth data for variable amplitude loading and are found to capture the overload effect with sufficient accuracy. Through a sensitivity analysis, fracture toughness is found to be the most dominant parameter in accelerating the crack length due to application of overload.

Fatigue crack growth in a diverse range of materials

This paper generally examines long crack growth data for a range of aerospace and rail materials tested at a variety of R ratios. The results of this study revealed that, for the 22 materials studied, the crack growth rate, da/dN, could be represented by a variant of the Hartman and Schijve equation with da/dN being proportional to the quantity (ΔK-ΔKth)α where α is approximately two. For cracking in 7050-T7451 it was also shown that this formulation holds for both long and small cracks, although a different value of ΔKth was required for small cracks compared to that required for long cracks. A possible explanation for this discrepancy is proposed and a methodology to estimate the small crack behaviour based on long crack data is presented. As such these observations have the potential to simplify the prediction of fatigue crack growth lives.