Stress Field Intensity Research Articles

A computational method of stress intensity factor for flat-oval cross-section thin-walled pipe

As an important parameter of fracture criterion, stress intensity factor (SIF) is considered to be one metric of the singular stress field intensity near the crack tip, also a main parametric in fracture mechanics. Therefore, solving technique on the stress intensity factor takes an important role in engineering applications. In view of typical three-dimensional features of flat-oval thin-walled pipes, it is relatively tough to obtain the stress intensity factors for the special-shaped shells with multi-transverse cracks by classical methods. In this paper, a very simple method based on J2-integral and bending theory is proposed to calculate the SIFs. Examples demonstrate that this technique is feasible, especially, that, suitable for the determination of the stress intensity factors of three-dimensional complicated structures. And the results show that not only the solution process is simple and available, but also the closed-form solutions can be derived effectively.

Consideration of Fracture Mechanism by Analysis of Intensity of Singular Stress Field and Fracture Surface Observation

Consideration of Fracture Mechanism by Analysis of Intensity of Singular Stress Field and Fracture Surface Observation

Intensity of singular stress field in bonded body under arbitrary material combination

Intensity of singular stress field in bonded body under arbitrary material combination

Strength Evaluation of Bonded Plate by the Fictitious Crack Method

In this study, the stress intensity factor of the crack near the interface in the adhesive bonded plate is analyzed and the interface strength evaluation of different material bonded plate is examined. A small edge crack near the interface is strongly controlled by the singular stress field at the interface end. The stress intensity factor of the crack near the interface in adhesive bonded plate is analyzed by changing the length and distance of the crack and the bond line thickness systematically. Based on the singular stress at the crack tip position, the approximate solution is presented. From the obtained results, the relationship between the critical stress intensity factor KIC and the interface strength is discussed. The critical stress intensity factor evaluated by the fracture stress converges to a constant value regardless of the bond line thickness. In other words, the stress intensity factor of the edge crack near the interface is the alternative parameter of the intensity of the singular stress field at the interface end, and it is useful for evaluating the adhesive strength of the bonded specimens.

一维六方压电准晶中正六边形孔边裂纹的反平面问题

The anti-plane problem of cracks near regular hexagonal holes in 1D hexagonal piezoelectric quasicrystals was studied. By means of the Cauchy integral formula in the complex variable functions and through construction of conformal mapping functions, the analytical solutions of stress distribution and field intensity factors at the crack tip near the hole were obtained under the electrically impermeable boundary condition. The effects of the edge length and the crack length of the regular hexagon as well as the shear stress on the field intensity factors were discussed with numerical examples.

Evaluation of Fatigue Strength of Butt Joint by Intensity of Singular Stress Field

In this study, the fatigue fracture criterion of the adhesively bonded joint is discussed. The singular stress field is formed at the interface end in the butt joint and causes the debonding fracture. The singular stress field is represented with the intensity of singular stress field (ISSF). The static debonding strength of the adhesively bonded joints is expressed with a constant value of critical ISSF. The rotating-bending fatigue tests are carried out on the butt joints of 15mm in diameter with four different adhesive thicknesses of 109 - 159μm, 209 - 265μm, 393 - 432μm and 754 - 841μm. The evaluation method by the ISSF is applied to the experimental results. It is found that the fatigue strength of the butt joint can be expressed with the constant value of critical ISSF.

Convenient Adhesive Strength Evaluation Method in Terms of the Intensity of Singular Stress Field

A convenient evaluation method is proposed for the debonding adhesive strength in terms of the intensity of singular stress field (ISSF) appearing at the end of interface. The same FEM mesh pattern is applied to unknown problems and reference problems. It is found that the ISSF is obtained accurately by focussing on the FEM stress at the adhesive corner. Then, the debonding condition can be expressed as a constant value of critical ISSF. The usefulness of the present solution is verified by comparing with the results of the conventional method.

Corrected stress field intensity approach based on averaging superior limit of intrinsic damage dissipation work

Corrected stress field intensity obtained by averaging the superior limit of intrinsic damage dissipation work in critical domain, which considers thoroughly thermodynamic consistency within irreversible thermodynamic framework, was proposed for predictions of high-cycle fatigue endurance limits. Simultaneously, the effects of mean stress, additional hardening behavior related to non-proportional loading paths and stress gradients on multiaxial high-cycle fatigue are taken into account in the proposed approach. The approach is an extension of the general stress field intensity. For a better comparison, existing multiaxial high-cycle fatigue criteria were employed to predict the endurance limits of different metallic materials subjected to different multiaxial loading paths, and it is shown that present proposal performs better from statistical value of error indexes, which make the proposed approach of corrected stress field intensity and its associated concepts provide a new conception to predict endurance limits of multiaxial high-cycle fatigue with high accuracy.

Most suitable evaluation method for adhesive strength to minimize bend effect in lap joints in terms of the intensity of singular stress field

The lap joint testing is designed to investigate the adhesive strength under pure shear loading. However, actually pure shear testing is very difficult to be realized in the experiment because of the bend deformation during testing causing the peeling force appearing at the adhesive region. To reduce the bend effect, this paper focuses on the intensity of singular stress field (ISSF) at the interface end in order to minimize the ISSF for lap joints. The results show that the ISSF decreases with increasing the adherend thickness. The minimum ISSF is obtained when the adherend thickness is large enough with the small deformation angle defined at the interface end. Since the strength of double lap joint (DLJ) is sometimes about two times larger than the strength of single lap joint (SLJ), the equivalent strength condition is discussed by changing adherend thicknesses of DLJ and SLJ. It is found that the strength of SLJ with adherend thickness t1 = 7 mm is nearly equal to that of double lap joint with t1 = 1.5 mm prescribed in Japanese Industrial Standard.

Validity of the Adhesive Strength Evaluation Method Based on the Intensity of Singular Stress Field in Two-Dimensional Modelling

Validity of the Adhesive Strength Evaluation Method Based on the Intensity of Singular Stress Field in Two-Dimensional Modelling

Intensity of singular stress field over the entire bond line thickness range useful for evaluating the adhesive strength for plate and cylinder butt joints

Our previous research has indicated that the bonded strength can be expressed in terms of the intensity of the singular stress field (ISSF). Since the ISSF is quite useful for evaluating the bonded strength, in this study, the variation of the ISSF is investigated over the entire bondline thickness range of plate and cylinder butt joints. Here, an effective mesh-independent technique combined with a standard FEM approach is used to obtain the ISSFs under arbitrary material combinations. A reference solution of simply bonded plate is used to eliminate FEM error since the exact ISSF is available. This paper clarifies the differences between the fracture behaviors of the bonded plate and cylindrical butt joints.

An analytical solution for the stress field and stress intensity factor in an infinite plane containing an elliptical hole with two unequal aligned cracks

The existing analytical solutions are extended to obtain the stress fields and the stress intensity factors (SIFs) of two unequal aligned cracks emanating from an elliptical hole in an infinite isotropic plane. A conformal mapping is proposed and combined with the complex variable method. Due to some difficulties in the calculation of the stress function, the mapping function is approximated and simplified via the applications of the series expansion. To validate the obtained solution, several examples are analyzed with the proposed method, the finite element method, etc. In addition, the effects of the lengths of the cracks and the ratio of the semi-axes of the elliptical hole (a/b) on the SIFs are studied. The results show that the present analytical solution is applicable to the SIFs for small cracks.

Fatigue life prediction of notched specimen for ultrahigh‐strength steel TM210A

AbstractThe effective stress model of the fatigue life prediction for notched components based on smooth specimens is presented. The model used surface area elements in the high‐stress region surrounding the root of a notch. The weakest link theory incorporating the stress field intensity model was used in this approach. The effects of stress gradient and component size were considered. A constant amplitude rotating bending fatigue experiment was performed at room temperature at stress ratio R = −1 for smooth and notched specimens of the ultrahigh‐strength steel TM210A. The proposed prediction method was checked against the experimental results of the TM210A notched specimens. Prediction results of 50% survival rate were all within a factor of 2 scatter band of the experimental results.

Practical method for analyzing singular index and intensity of singular stress field for three dimensional bonded plate

In this paper, the practical analysis methods are proposed for analyzing the singular index and the intensity of singular stress field (ISSF) at the vertex of the interface in the three dimensional (3D) bonded plate. The analysis methods focus FEM stresses at and around the vertex. The singular index is determined from the FEM stress ratio at the vertex obtained by performing FEM analyses on the finely and coarsely meshed models. Then, the ISSF is determined by the ratio of the average FEM stresses at and around the vertex obtained by performing the FEM analyses on the reference and unknown models under the same mesh pattern. The validity of the present methods was examined by the plane strain bonded plate and 3D bonded plate in the literature. It was found that the present methods for the singular index have the same accuracy as the FEM eigenvalue analysis. The asymptotic solutions with the singular index and ISSF by the present method correspond to FEM stress distributions. Since the ISSF by the body force method (BFM) is used as the reference solution, the present method for ISSF has the same accuracy as BFM. Moreover, the critical ISSF values were calculated in the experimental results of the butt joints with various adhesive thicknesses. In the case of the ductile epoxy adhesive, it was shown that the critical ISSF at the vertex by 3D model was more constant against the thickness than that by 2D model. The result is quite different from that of the brittle epoxy adhesive and can be never obtained by 2D model.

Energy-based low cycle fatigue indicator prediction of non-load-carrying cruciform welded joints

A new uniform analytical formulation is proposed to predict the low cycle fatigue assessment indicator of non-loading cruciform welded joints under tensile cyclic loading considering the effects of plasticity and mechanical heterogeneity of the welded materials and geometry configurations. Particularly, weld toe of the joints is dealt with a notch rounding in order to avoid the notch tip singularity in accordance with generalized Neuber concept of Fictitious Notch Rounding (FNR). The relationship between elastic and plastic energy concentration factor of weld toe is firstly determined by the combination of notch stress and strain distribution with the increases of nominal loading, then the main parameters affecting the energy concentration factor are investigated by separating elastic and plastic stages. Stress and strain field intensities are finally expressed in terms of total energy values, which are linked to the nominal energy ones. The energy prediction function which takes into account the material and geometry factors is capable of providing a closed form analytical expression about the state of energy both under small and large-scale yielding for industrial facilities by the comparison against finite element analysis results.

Intensity of singular stress field for three-dimensional butt joint to evaluate the adhesive strength

Adhesive joints are extensively used in various manufacturing processes in different industrial sectors because of its high fatigue resistance. Different materials properties cause the singular stress field, whose intensity is depending on the adhesive joint geometry. Our previous studies show that debonding strength can be expressed as a constant value of the critical intensity of singular stress field (ISSF) by using two-dimensional butt joint models. By considering real specimen geometry, in this paper, the ISSFs on the interface outer edges of three-dimensional butt joints are analysed by varying the adhesive thicknesses. A mesh-independent technique combined with three-dimensional finite element method (FEM) is shown to evaluate the ISSF. The ISSF distributions on the interface outer edges are analysed in comparison with the previous two-dimensional results. It is found that the critical ISSF considered 3D geometry is almost constant independent of the adhesive thickness.

Intensity of Singular Stress Field for Three-Dimensional Butt Joint to Evaluate the Adhesive Strength

Intensity of Singular Stress Field for Three-Dimensional Butt Joint to Evaluate the Adhesive Strength

Analysis on Intensity of Singular Stress Field on the Interface Outer Edge of Three-Dimensional Butt Joint with Fillet

Analysis on Intensity of Singular Stress Field on the Interface Outer Edge of Three-Dimensional Butt Joint with Fillet

Field Stress Intensity Calculation of Notched Component Specimens based on Field Intensity Method

Field Stress Intensity Calculation of Notched Component Specimens based on Field Intensity Method

Hydraulic fracture at the dam-foundation interface using the scaled boundary finite element method coupled with the cohesive crack model

The scaled boundary finite element method coupled with the cohesive crack model is extended to investigate the hydraulic fracture at the dam-foundation interface. The concrete and rock bulk are modeled by the scaled boundary polygons. Cohesive interface elements model the fracture process zone between the crack faces. The cohesive tractions are modeled as side-face tractions in the scaled boundary polygons. The solution of the stress field around the crack tip is expressed semi-analytically as a power series. Accurate displacement field, stress field and stress intensity factors can be obtained without asymptotic enrichment or local mesh refinement. The proposed procedure is verified by the hydraulic fracture of a rectangular embankment on rigid foundation and applied to the modeling of hydraulic fracture on the dam-foundation interface of a benchmark dam. Different distributions of water pressure inside the crack are investigated. It is found that the water pressure inside the crack decreases the peak overflow to less than 20% of the case without water in the crack. Considering the water lag or not is significant to the response, while different distribution of pressure following the water lag region in the fracture process zone has negligible influence.