Effect Of Initial Crack Length Research Articles

The Effect of Load Steps and Initial Crack Length on Stress Distribution of Fiber Metal Laminates

Fiber Metal Laminates (FMLs) are advanced composite materials composed of alternating layers of fiber-reinforced composites and metal sheets, offering a unique blend of high strength, stiffness, and fatigue resistance. Understanding the behavior of FMLs under different loading conditions, particularly in the presence of initial cracks, is crucial for predicting their structural integrity and performance. This study investigates the effect of initial crack length and load steps on the stress distribution within FML structures through numerical simulation. A glass fiber-reinforced epoxy (GFRE) composite is constituted by glass fibers in off-axis directions of 0o/90o. The crack length of 3 mm, 6 mm, 9 mm, and 12 mm is initially defined on the side of fiber metal laminates. The tensile load was gradually applied to the laminates for five different ratios. The ratios are defined by dividing the tensile load with the area of the laminates which is then called stress ratio. The results show that the greater the initial crack length and load step ratio, the greater the stress around the crack tip. The stress distribution in each layer of the laminates shows different characteristics between tensile and compressive. This will affect the crack propagation behavior of the laminates. Moreover, the findings also provide valuable insights for optimizing FML design, improving damage tolerance, and extending service life in diverse engineering applications.

Effect of initial crack length, cross-head speed, and quenching on the fracture toughness of HDPE with and without UV stabilizers

Effect of initial crack length, cross-head speed, and quenching on the fracture toughness of HDPE with and without UV stabilizers

Numerical Investigation on Crack Propagation of Three-Dimensional Pipeline Under Seismic Wave Loading

Cracks in transport pipelines significantly impact their structural safety, making pipeline fracture damage a major concern. While experimental tests can study crack growth, their setup and costs are substantial. To address this, our work involves parametric analyses to investigate the effects of initial crack length, load types and sizes, and pipe wall thickness on the crack tip stress field. The finite element model is established according to the actual operation, and the crack defects of the pipe are established by the extended finite element method (XFEM). The crack tip variation is studied by extracting the von Mises stress and strain at the crack tip. When the crack propagates, the stress field at the crack tip will fluctuate in a certain range. The relationship between stress field fluctuation and crack propagation was studied by changing the XFEM crack growth for comparative analysis. Utilizing 429 numerical results obtained from a parametric numerical model implemented with Python and Abaqus, we establish a back propagation (BP) neural network prediction model to forecast the stress field at the crack tip. The relative errors between the numerical results and the predictions by our model remain below 5%. In conclusion, our proposed approach for analyzing pipeline fracture under multiple loads proves valuable for pipeline safety assessment, and it offers useful insights for evaluating the suitability of transportation pipelines.

Hydraulic Fracturing Breakdown Pressure and Prediction of Maximum Horizontal In Situ Stress

Using the presented criteria for the breakdown pressure in which the breakdown pressure is related to the horizontal stress, the breakdown pressure in the hydraulic fracturing test is directly used in the estimation of the maximum horizontal in situ stress. However, the classical breakdown pressure criteria do not take into account the effects of near-wellbore stress field, so estimating the horizontal stress using them is accompanied by errors. A plane strain numerical model is presented to obtain the breakdown pressure, in which the effect of initial crack length are considered. In this model, it is assumed that the rock medium is impermeable and the breakdown occurs at the tip of two radially cracks. Thus, in this model, the effect of the initial crack length, which is not present in the classical models, is considered. The results obtained from the numerical model show the significant effect of the initial crack length on the breakdown pressure. Also, the comparison of the numerical model with the classical criteria shows that the condition of using the classical criteria to determine the breakdown pressure is that the ratio of the initial crack length to the borehole radius is very small. Using the numerical model, 1,456 datasets were prepared to train an artificial neural network to predict the maximum horizontal stress. Input parameters include breakdown pressure, minimum horizontal stress, initial crack length, and tensile strength. The evaluation of the results shows that the obtained neural network model has a good ability to predict the maximum horizontal stress.

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.

The effects of welded clips on fatigue crack growth in AA6156 T6 panels

Fatigue crack growth in different panels, made of AA6156 T6, was investigated experimentally and numerically. Three different types of panels were used, simple one, so-called base metal (BM), panel with 4 welded stringers and panel with 4 welded stringers and 3 welded clips. Experimental investigation indicated benefits of stringers, especially in respect to residual life, since the number of cycles were more than doubled (420 Kcyc vs 195 Kcyc for initial crack length 14 mm), but that was not the case for panels with clips (220 Kcyc). Experimental investigation was also performed on panels with longer cracks (75 mm) to check the effect of initial crack length in the case of BM and panels with 4 stringers, showing practically the same effect of stringers on residual life (95 Kcyc vs 50 Kcyc). Then, fatigue crack growth in panels was simulated numerically using xFEM. Numerical simulation indicated the same trend and effectiveness of stringers, with sufficient agreement with experimental results for BM and panels with stringers only. Anyhow in the case of clips panels with 4 stringers and 3 clips, number of cycles for panel with additional 3-clips was higher than for panel with just 4-stringer, (278 Kcyc vs 265 Kcyc), improving fatigue life for cca 5 %, contrary to experimental results.

Numerical investigation on central tearing behaviors and propagation mechanisms of coated warp-knitted fabrics

To reveal the central tearing behaviors and propagation mechanisms of the architectural non-crimp fabric (NCF) composites with an initial crack, a microscopic finite element (FE) model was proposed and developed to simulate the tearing propagation process of materials in this paper. Firstly, the experimental program including the central crack tearing test of NCF composites and uniaxial tensile test of yarns was performed for gaining the material parameters. Secondly, a finite element (FE) model was developed and validated from the good agreement between numerical and experimental results. Furthermore, tearing damage mechanisms and failure performances of the NCF composites with an initial central crack were simulated and analyzed. Finally, the effects of initial crack length, yarn orientation, and arch curvature of weft yarn on mechanical properties were investigated in depth. The analysis and comparison results indicate that the NCF composite shows the unneglectable orthotropic characteristics, in which the initial crack length, yarn orientation, and arch curvature of weft yarn have the significant effects on the mechanical properties. This paper thus provides an adequately feasible and accurate FE model for the numerical simulation on the central tearing propagation behaviors of the NCF composites with an initial crack.

Paintings crack initiation time caused by microclimate

The current paper aims to use an irreversible cohesive zone model to investigate the effects of temperature and relative humidity cycles on multilayer thin-film paintings. The homogenous one-dimensional paint layers composed of alkyd and acrylic gesso over a canvas foundation (support) with known constant thicknesses are considered as the mechanical model of painting. Experimental data was used for mathematical modeling of canvas as a linear elastic material and paint as a viscoelastic material with the Prony series. Growth of crack through the length of the paint layers under the low amplitude cyclic stresses are modeled by cyclic mechanical loadings. The three-dimensional system is modeled using a finite element method. Fatigue damage parameters such as crack initiation time and maximum loads are calculated by an irreversible cohesive zone model used to control the interface separation. In addition, the effects of initial crack length and layers thickness are studied. With the increase of the painting thickness and/or the initial crack length, the value of the maximum force increases. Moreover, by increasing the Relative Humidity (RH) and the temperature difference at loading by one cycle per day, the values of initiation time of delamination decrease. It is shown that the thickness of painting layers is the most important parameter in crack initiation times and crack growth rate in historical paintings in museums and conservation settings.

Uniaxial tearing properties and the tearing residual strength models of PTFE coated fabric

This study presents an experimental and analytical investigation on central crack tearing properties of PTFE coated fabric. Firstly, tearing tests under uniaxial tension load were carried out to investigate the influence of crack length and crack orientation on tearing properties of PTFE coated fabric. Tear failure process was carefully recorded and two types of failure modes can be characterized, i.e. progressive failure and brutal failure. The effect of initial crack length and orientation on tearing residual strength (TRS) can be attributed to the numbers of the cut yarns, which can be represented by the equivalent crack length. Secondly, the available TRS models are summarized and discussed in detail. It is found that these models can be classified into two types, i.e. fracture-mechanic-based models and stress-field-based models. By comparing the prediction results with test data, these models present to be only valid for small crack conditions, and the stress-field-based model shows better accuracy.

Study on creep damage and crack growth for TC11 under complex stress loading

In order to investigate the creep damage and creep crack growth of TC11, we established the finite element model based on ductility exhaustion constitutive model. This paper uses the uniaxial creep test of TC11 at 500℃ as a reference and studies the effect of initial crack dimensions on crack growth of CT specimen and surface crack specimen. The initial crack length of CT specimen has a significant effect on creep crack growth of TC11 material. The larger the initial crack length, the higher the crack growth rate, the crack tip equivalent stress and the crack tip stress triaxiality. The initial crack length has a greater influence on creep crack growth for deep crack specimens(a0/W=0.6, a0/W=0.7) than that for shallow crack specimens(a0/W=0.3, a0/W=0.4, a0/W=0.5). When the stress intensity factor Kπ/2 at the deepest location of surface crack is the same, the crack growth length of each specimen in the depth direction at the same time is approximately twice as much as that in the length direction. With the increase of initial crack size, the crack growth rate of surface crack decreases gradually. And the effect of initial crack length on crack growth is greater than that of initial crack depth.

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.

Tearing behavior of membrane coated fabrics based on the DIC method under the effect of initial crack length

Abstract In this work, the digital image correlation (DIC) procedure is applied to experiments involving the tearing behavior of membranes under the effect of initial crack length, to obtain the displacement and corresponding strain results image and data of the tensile process, which intuitively shows the changes in the tearing process of the membrane. The experimental results and the analytical solution of the displacement of the orthotropic material in the fracture mechanics are compared and analyzed to verify the reliability of the theoretical model. Based on the theoretical model and the displacement values measured, mixed-mode (I, II) stress intensity factors at different angles of the crack tip are analyzed. This will make it possible to analyze the crack propagation law of the membrane and also provide a more effective measurement method and calculation method for a tearing test of orthotropic material under tensile loading.

Effect of initial crack length on the transition of fatigue properties for precipitation hardened steel

Effect of initial crack length on the transition of fatigue properties for precipitation hardened steel

The effects of initial crack length on fracture characterization of rubbers using the J-Integral approach

The effects of initial crack length on the mode I fracture properties of crosslinked elastomers were investigated. A J-integral approach was implemented using single-specimen test procedures. Quasi-static fracture tests were carried out on filled and unfilled acrylonitrile-butadiene rubbers with various pre-cut (initial) crack lengths, a0, at a fixed rate of extension, using single edge notch rectangular bar specimens. Data from these experiments were analyzed and crack resistance curves (R curves) were obtained. A detailed analysis of the single-specimen method was carried out to establish correlation with the fracture properties derived from the more involved multi-specimen method. The weak dependence of geometry factor on rubber composition and displacement (in the neighborhood of crack initiation displacement) was verified. The crack initiation resistance and tearing modulus of the materials were calculated based on the R curve for each initial crack length. Fracture properties of lightly cracked specimens (a0/W<0.4, where W is the specimen width), including crack initiation resistance, strain at crack initiation, tearing modulus and maximum load and extension before fracture, were found to show significant variations with a0. These variations are characterized and discussed for the filled and unfilled rubber materials.

Effect of Initial Crack Length of C(T) Specimen on Crack Propagation Measurement by Dc Potential Drop Method

The compact tensile specimens (C(T) specimens) are commonly used in crack propagation tests. The DC potential drop method is an important method for measuring crack length in crack propagation tests. To investigate the influence of the initial crack length of the C(T) specimen on the calibration curve in practice, the variation law of the potential field distribution of the compact tensile specimen with the crack propagation has been studied. The measurement features in different initial crack lengths and different current injection positions were quantitatively analyzed. The results show that the initial crack length has a significant effect on the sensitivity of the signal and the linearity of the calibration curve. The sensitivity can be improved by increasing the initial crack length, while the linearity decrease.

A novel cohesive zone model to simulate ductile adhesives in automotive structure metallic joints

In recent years, increasing utilize of the adhesively bonded joints due to its prominent features in distribution of the stress in bonded area and bonding dissimilar material has led to developing its computational aspects to provide more reliable response. In this regard, cohesive zone model (CZM) as an effective method to simulate bondline is introduced. The crucial aspect of this method is the determination of the relation between traction and separation in fracture process zone (FPZ). In fact, the traction-separation law (TSL) is a material model which must be properly obtained and applied to the adhesive bondline. According to the literature, mechanical response of the adhesive joints in most cases (especially in ductile and semi-brittle adhesives) is depended on the TSL curve shape. In this study, a novel CZM is developed to simulate double cantilever beam (DCB) adhesive joint. The main advantageous this new model is considering non-linear behavior of ductile adhesives in elastic region. DCB coupons fabricated by means of Al 6061 adherends and Araldite 2015 adhesive. After direct extraction of the TSL and obtaining cohesive parameters of the new model, numerical simulation of the DCB is conducted. Finally, sensitivity analysis of cohesive parameters and effect of initial crack length on the DCB response is investigated.

Damage tolerance and classic fatigue life prediction of a helicopter main rotor blade

Fatigue life of the main rotor blade of a helicopter is investigated from two different approaches. The blade is comprised of many different parts such as spar, skin, abrasive strip, doublers, box beam doublers, etc. and it undergoes complex random load spectra. A finite element analysis is carried out to assess the stress distribution in the blade parts. Then, using the Miner’s rule the fatigue life of the blade is calculated following a classic life estimation method under random loading. At the next step, damage tolerance approach is used for life estimation of the blade. Fatigue crack growth properties and threshold stress intensity range of the spar is obtained based on ASTM E647 test method. Then, crack growth analysis is done using Zencrack software. In order to calculate the length of the smallest growing cracks and their fatigue crack growth life, no crack growth and slow crack growth approaches are used. A comprehensive investigation is carried out on the effect of initial crack length and aspect ratio on growth or no growth of cracks. Comparing the obtained fatigue life from two different approaches, some conclusive results are drawn.

Damage tolerance approach for analyzing a helicopter main rotor blade

In this article, damage tolerance approach is used for life estimation of the main rotor blade of a helicopter under random loading. At first, fatigue crack growth properties and threshold stress intensity range of the spar is obtained based on ASTM E647 test method. Then, crack growth analysis is done using Zencrack software. In order to calculate the length of the smallest growing cracks and their fatigue crack growth life, no crack growth and slow crack growth approaches were used. A comprehensive investigation was carried out on the effect of initial crack length on growth or no growth of cracks.

Initial crack length on the interlaminar fracture of woven carbon/epoxy laminates

This paper describes an experimental and numerical study developed to characterize the mode I fracture toughness of woven carbon/epoxy composites, using Double Cantilever Beam (DCB) tests. The laminates were manufactured using an epoxy resin and twelve woven balanced bi-directional layers of carbon fibres, all of them with the same orientation (0/90 °). The interlaminar fracture toughness shows to be practically independent of the initial crack length and the value of GIC, obtained according with the modified beam theory, was about 282 J/m2. Numerical analysis based on the finite element method was also developed to understand the effect of initial crack length. After a mesh refinement study, the numerical predictions were compared with experimental results which validated the model. The total energy dissipated by the specimen is nearly constant. The size of cohesive zone ahead of crack tip is also independent of the initial crack length (a0).

Effect of initial crack length on the measured bridging law of unidirectional E-glass/epoxy double cantilever beam specimens

In this paper, the effect of initial delamination length is experimentally investigated on obtaining the mode I bridging law of unidirectional E-glass/epoxy double cantilever beam (DCB) specimens manufactured by hand layup method. To this end, an experimental test set-up is established for accurate measurement of crack tip opening displacement (CTOD) using digital image processing method. DCB tests are performed for three different delamination lengths and the corresponding bridging laws are calculated using J-integral approach. Results showed that the maximum bridging stress, the shape of bridging law and energy dissipation in bridging zone are slightly affected by changing initial crack length. In other words, the measured bridging law acts independent of initial delamination length. Therefore, the obtained bridging law can be used with the cohesive elements available in the commercial finite element software to simulate the delamination propagation behavior in unidirectional DCB specimens.