Key-hole Notches Research Articles

Closed-form expressions of mode I apparent notch fracture toughness for key-hole notches

Two closed-form expressions were developed in this research to estimate the mode I apparent notch fracture toughness of brittle materials weakened by key-hole notches based on the well-established brittle fracture criteria, namely, the point stress and the mean stress. The theoretical models were verified using the experimental results reported in open literature dealing with tensile fracture in rectangular isostatic graphite plates containing central key-hole notches of various notch tip radii. A very good agreement was found to exist between the predictions of both the models and the experimental results. The results showed that while the accuracy of each model was different for various notch tip radii, total accuracies of the two models were almost equal (both about 93%) demonstrating their effectiveness. Using such expressions, it is expected that one can simply estimate the load-carrying capacity of brittle and quasi-brittle components weakened by key-hole notches under mode I loading.

Stress-based criteria for brittle fracture in key-hole notches under mixed mode loading

Abstract Two stress-based failure criteria were developed in the present research to predict mixed mode I/II brittle fracture in engineering components weakened by a key-hole notch. The first criterion was based on the well-established maximum tangential stress (MTS) concept, successfully proposed and utilized several times in recent years for different notch features. The second one was on the basis of the mean-stress (MS) concept which has been frequently used for predicting pure mode I fracture in notched domains. The results of the criteria were represented in the form of fracture curves and the curves of fracture initiation angle in terms of the notch stress intensity factors. To verify the validity of the fracture models, the theoretical predictions were compared with a large bulk of experimental data, reported in literature, on the fracture of rectangular isostatic graphite plates weakened by central key-hole notches of five different tip radii. It was found that while the total accuracies of the criteria are very good, for small notch tip radii, the MTS criterion provides generally better mixed mode notch fracture toughness results than the MS criterion. Conversely, the MS criterion works much better than the MTS model for larger notch tip radii. Dealing with fracture initiation angle, both the criteria could estimate the experimental results successfully.

Study on stress fields near V-notch tip with end-hole under in-plane and out-of-plane conditions

This paper deals with the asymptotic stress fields for V-notch problems with end-holes, including keyhole notches, namely a slit ending with a circular hole. Based on the superposition method and the conventional Mode III stress field for a sharp Vnotch, the approximate solution for stress field of V-notch with end-hole under out-of-plane shear loading is proposed. This work also shows results of the evaluation on the accuracy of the Mode I and II stress fields for V-notch with end-hole proposed in the previous study by the authors. The stress fields are written in terms of the notch stress intensity factors (NSIFs), and the NSIFs are determined by means of numerical analyses. The effectiveness and validation of the proposed superposition approach are discussed by comparing the results from the present approach with those taken from the literature.

Application of the Notch Stress Intensity and Crack Propagation Approaches to weld toe and root fatigue

Several fatigue failures are initiating from the root of non-penetrating welds, which are widely applied in several industrial sectors. The structural optimization and reduction of weld material increase the danger of root cracking. The fatigue assessment during design is mainly based on the nominal, structural hot-spot or notch stress approach. These approaches are only partly applicable to weld roots, give rough estimates such as the nominal stress approach or over-conservative life estimation such as occasionally the notch stress approach when keyhole notches are modelled. An alternative assessment is possible with the crack propagation approach assuming the non-welded root gap and a short crack at the weld toe as initial cracks. A new approach is the notch stress intensity approach (N-SIF approach) which is able to assess the fatigue life of V-shaped notches at weld toes as well as crack-like notches at weld roots using the strain energy density around the notch. Both approaches are applied to different joints where toe and root failures are probable. The results are compared with a previous analysis using the notch stress approach. Fatigue test results are also available for a comparison which allows to draw conclusions with respect to the approaches for an appropriate fatigue strength assessment.

Fatigue‐relevant stress field parameters of welded lap joints: pointed slit tip compared with keyhole notch

ABSTRACTThe notch stress intensity factor (NSIF) based analytical frame is applied to the slit tips (or weld roots) of welded joints with inclusion of the T‐stress component. This T‐stress can be determined from FE models evaluating the ligament stresses close to the pointed slit tip. An alternative analytical frame is presented for the corresponding keyhole notches based on analytical solutions from the literature, which are applied to the ligament stresses.In the slit tip models, the mean local strain energy density (SED) with inclusion of the T‐stress effect is determined analytically and numerically in comparison, using two different fatigue‐relevant control radii, R0= 0.28 mm and R0= 0.15 mm, the former value well proven for thick‐sheet welded joints made of structural steel. The latter smaller value is tentatively proposed for thin‐sheet welded joints, in the direction suggested in the recent literature where a reduction of the microstructural support length for laser beam welds and resistance spot welds is recommended. The FEM‐based and analytical stress concentration factors (SCF) for the lap joint keyhole model and also the SED values for the corresponding pointed slit tips are found to be in good agreement. The J‐integral consisting of the first and second component (the latter containing the T‐stress) is compared with the corresponding SED values.

Corrosion Fatigue of AZ91E-T6 Cast Magnesium Alloy in a 3.5 Percent NaCl Aqueous Environment

The objective of this research was to obtain and compare constant and variable amplitude fatigue behavior of AZ91E-T6 cast magnesium alloy in both an air and 3.5 percent NaCl aqueous corrosive environment. An additional objective was to determine if commonly used models that describe fatigue behavior and fatigue life are applicable to this material and test environment. Fatigue tests included constant amplitude strain-controlled low cycle fatigue with strain ratio, R, equal to 0, −1 and −2, Region II constant amplitude fatigue crack growth with load ratio, R, equal to 0.05 and 0.5 and variable amplitude fatigue tests using keyhole notched specimens. In all fatigue tests, the corrosion environment was significantly detrimental relative to the air environment. Mean strains influenced fatigue life only if accompanied by significant mean stress. The Morrow and Smith, Watson, and Topper mean stress models provided both accurate and inaccurate fatigue life calculations. Likewise, variable amplitude fatigue life calculations using the local strain approach and based upon the formation ofal mm crack at the keyhole notch were both accurate and fairly inaccurate depending on the specific model used.

Estimation Of Local Cyclic Stress Ratio Due To Confined Notch Plasticity

Estimation Of Local Cyclic Stress Ratio Due To Confined Notch Plasticity