Search

This paper deals with the application of fracture mechanics approaches for predicting the residual static strength and the crack kinking angle of adhesively bonded joints containing interfacial edge pre-cracks. The interfacial cracks are created due to different factors such as inappropriate surface preparation which cause a significant reduction of the joint strength. To investigate the residual strength of interfacial cracked adhesive joints and predict the crack kinking angle, three different approaches including the maximum tangential stress (MTS), the minimum strain energy density (SED) and the maximum tangential strain energy density (MTSED) were assessed. To this end, single lap joints (SLJs) containing a brittle adhesive material and with different pre-crack sizes and various substrate thicknesses were manufactured and tested. The results were also verified by applying fracture mechanics approaches on previously published experimental data. According to the results, it was concluded that in mode II dominant cases, the predictions of kinking angle using the MTS method was in good agreement with the experimental observations, while in mode I dominant cases the mentioned approach provided poor predictions. It was also found that the SED criterion could be a precise model for predicting the crack extension angle in mode I dominant conditions. The results also showed that the MTS criterion predicts the residual static strength of interfacial cracked adhesive joints very well. [ABSTRACT FROM AUTHOR]

Abstract: Finite element method is used to analyze a rail with a vertical bottom up crack at its foot, under the axle load and surface traction of a wheel. The possibility of crack formation at the foot of the rail in the neighborhood of a welding connection is discussed. A brief review on the importance of T‐stress in brittle fracture is presented. Seven cases with different locations of the crack relative to rail's sleeper contact region are considered. Numerous positions of the wheel are considered, and in each case, 3 crack parameters KI, KII, and T‐stress are calculated. Then, the biaxiality ratio and the mixity parameter for each loading and crack condition are calculated. It is shown that the location of crack and wheel can create mixed mode loading in the cracked rail and that the magnitude of crack tip parameters are strongly dependent on these geometric variables. In particular, the magnitudes of T‐stress and biaxiality ratio are significant in some cases. The effect of friction between the crack faces in the presence of compressive mode I loading on the mode II stress intensity factor is studied. Under mixed mode loading, due to the axle load and surface traction, the most critical condition is the formation of vertical cracks near the sleeper contact region. [ABSTRACT FROM AUTHOR]

In laboratory fracture toughness studies, the crack growth resistance of rock materials may be influenced by different factors such as specimen geometry, loading conditions, and also the type of pre-notch cut in the test sample. In this paper, a large number of mode I fracture toughness experiments are conducted on an Iranian white rock “Harsin marble” with six different mode I specimens. The selected test specimens are in the shape of cylindrical rod, rectangular beam, and circular Brazilian disk containing either chevron notch or straight crack. The effect of specimen geometry and pre-notch type was investigated statistically, and it was found that the average fracture toughness values of notched specimens were higher than those of the similar specimens but containing straight crack. Meanwhile, the scatters of fracture toughness data for chevron notched specimens were smaller than those for the straight cracked samples. For each set of experimental fracture toughness results, probability of fracture was investigated using two- and three-parameter Weibull statistical distributions. Comparison of the Weibull fitted curves for chevron notched and straight cracked samples with the same geometries demonstrated that the discrepancy between the corresponding curves can be described with a good accuracy by a simple shift factor. In addition, using the extended maximum tangential strain criterion which takes into account the influence of both KI and T-stress terms, the statistical fracture toughness data of chevron notched specimens were predicted in terms of the Weibull distribution parameters of the straight cracked specimens. [ABSTRACT FROM AUTHOR]

Several studies have dealt with the application of the generalized stress intensity factor (GISF) on the failure load prediction of adhesive joints. However, the effect of geometry on the critical value of the GSIF (Hc) is complex and limits its application. Due to the effect of multiple geometrical features and the limited success in the field of adhesive joints, a statistical analysis is a possibility. This paper investigates the impact of different geometrical features on theHcin single lap adhesive joints. To achieve this, the statistical response surface methodology (RSM) was used to design the experiments and for the statistical analysis. According to the RSM, 31 arrangements of single lap joints were manufactured and tested. In this analysis, the adhesive thickness, adherend thickness, overlap length and also the free length, each in five different levels, were considered. The effect of linear, quadratic and two-way interactions of the geometrical parameters on theHcand failure load were also studied. It was shown thatHcis most affected by the overlap length. Variation ofHcin term of the free length is by far higher at lower adhesive thicknesses. Also, the effect of substrate thickness onHcis more considerable for thinner bondlines. The interactions of overlap length/free length and overlap length/adhesive thickness affect the failure load more considerably than the other studied interactions. The effect of free length on the failure load increases with the bondline thickness, while the effect of substrate thickness is stronger for a lower adhesive thickness. [ABSTRACT FROM PUBLISHER]

Interface strength is considered as one of the most influential factors in the long-term durability of the replaced joint in cemented total hip replacement. Several researchers have suggested that the damage initiation in a replaced joint is a mechanical phenomenon primarily taking place in the vicinity of cement-prosthesis interface. In this study, the fracture behavior of a crack at the interface of cement-prosthesis was investigated both experimentally and theoretically under static loading conditions. The finite element method, and then the maximum tangential stress (MTS) and the generalized MTS (GMTS) criteria were used for theoretical study of interface fracture. Some experiments were also carried out to investigate the effect of cement mixing methods (hand mixing and vacuum mixing) on crack growth pattern. The results showed that the vacuum-mixed cement led to self-similar crack growth along the cement-prosthesis interface, while the crack kinked into the cement in the samples prepared by hand-mixed cement. Then some experiments were performed to verify the theoretical results obtained for mixed mode fracture angles in the samples prepared by hand-mixed cement. The sandwich Brazilian disk model was used in both finite element and experimental approaches to simulate the cement-prosthesis interface. The experimental results were found to be in good agreement with those predicted by the GMTS criterion. [ABSTRACT FROM AUTHOR]

A new approach based on the maximum tangential stress (MTS) criterion has been employed for investigating mixed mode brittle fracture in materials like polycrystalline graphite. The new criterion has been examined using the experimental results reported in the literature for several graphites. The reported experimental data were obtained from fracture tests conducted using the centrally cracked Brazilian disk specimens. It is shown that the values of mixed mode fracture resistance predicted by the new criterion are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

ABSTRACT The crack growth retardation is studied theoretically by drilling two symmetric holes at appropriate locations along the crack flanks. A fatigue crack growth code for two-dimensional elastic problems is developed to approve the effectiveness of this method. The crack growth retardation was examined using a parametric study both on the arrangements of the flank holes and the diameters of holes. The numerical results reveal that for some cases, the presence of flank holes significantly decreases the stress concentration around the crack tip and its stress intensity factor. The best positions for crack flank holes to provide the highest crack growth retardation are shown to be where the line connecting the two centres of holes passes the crack tip. A larger hole diameter and a closer distance between the flank holes and the crack tip result in lower crack growth rate and higher fatigue life. [ABSTRACT FROM AUTHOR]

ABSTRACT The edge-cracked beam specimen subjected to anti-symmetric four-point bend (ASFPB) loading has been conventionally used in the past for investigating the pure mode II fracture experiments in many engineering materials. However, it is shown through finite element analysis that the ASFPB specimen sometimes fails to produce pure mode II conditions. For anti-symmetric loads applied close to the crack line, there are considerable effects from KI and T-stress in the ASFPB specimen. Pure mode II is provided only when the applied loads are sufficiently far from the crack plane. [ABSTRACT FROM AUTHOR]

Different laboratory experiments are usually conducted to characterize the fracture behaviour and integrity properties of newly developed structural materials. However, the reported fracture tests data for an improved high strength cement mortar (HSCM) under combined tension-shear loading are not in agreement with theoretical predictions obtained from well-known fracture criteria. It is shown in this paper that the significant difference existing between the experimental and theoretical results is due to ignoring the effect of T-stress on the processes of crack growth in the HSCM test specimens. A modified fracture model is then used to show that the theoretical predictions can be corroborated by the experimental results when the effect of T-stress is taken into account. [ABSTRACT FROM AUTHOR]

A ring shaped specimen is used for studying mixed mode fracture in brittle materials. The ring specimen is subjected to a compressive diametral load and contains two angled central cracks. A series of fracture tests are conducted under various mode mixities using the ring specimen. It is shown that the obtained experimental results are in a very good agreement with theoretical predictions of the modified maximum tangential stress criterion. [ABSTRACT FROM AUTHOR]

Applications of fracture mechanics in the strength analysis of ceramic materials have been lately studied by many researchers. Various test specimens have been proposed in order to investigate the fracture resistance of cracked bodies under mixed mode conditions. Double Cleavage Drilled Compression (DCDC) specimen, with a hole offset from the centerline is a configuration that is frequently used in subcritical crack growth studies of ceramics and glasses. This specimen exhibits a strong crack path stability that is due to the strongly negative T-stress term. In this paper the maximum tensile stress (MTS) criterion is employed for investigating theoretically the initiation of brittle fracture in the DCDC specimen under mixed mode conditions. It is shown that the T-stress has a significant influence on the predicted fracture load and the crack initiation angle. The theoretical results suggest that brittle fracture in the DCDC specimen is controlled by a combination of the singular stresses (characterized by KI and KII) and the non-singular stress term, T-stress. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to revisit the maximum tensile stress (MTS) criterion to predict brittle fracture for mixed mode conditions. Earlier experimental results for brittle fracture of polymethylmethacrylate (PMMA) using angled cracked plates are also re-examined. The role of the T-stress in brittle fracture for linear elastic materials is emphasized. The generalized MTS criterion is described in terms of mode I and II stress intensity factors, K[sub I] and K[sub II] and the T-stress (the stress parallel to the crack), and a fracture process zone, r[sub c]. The generalized MTS criterion is then compared with the earlier experimental results for PMMA subjected to mixed mode conditions. It is shown that brittle fracture can be controlled by a combination of singular stresses (characterized by K) or non-singular stress (T-stress). The T-stress is also shown to have an influence on brittle fracture when the singular stress field is a result of mode II loading. [ABSTRACT FROM AUTHOR]