Evaluation of debonding strength of single lap joint by the intensity of singular stress field

In this paper, the similarity of the singular stress field of the single lap joint (SLJ) is discussed to evaluate the debonding fracture by the intensity of the singular stress field (ISSF). The practical method is proposed for analyzing the ISSF for the SLJ. The analysis method focuses on the FEM stress at the interface end by applying the same mesh pattern to the unknown and reference models. It is found that the independent technique useful for the bonded plate and butt joint cannot be applied to the SLJ because the singular stress field of the SLJ consists of two singular stress terms. The FEM stress is divided to two FEM stresses by applying the unknown and reference models to different minimum element sizes. Then, the practicality of the present method is examined by applying to the previous tensile test results of the SLJ composed of the aluminum alloy and the epoxy resin. The ISSFs for the SLJ were calculated by changing the adhesive thickness t2 and the overlap length l2. In the case of the SLJ with 225mm in total length and 7mm in adherend thickness, it was found that the similar singular stress fields are formed in the range of 0.15mm ≤ t2 ≤ 0.9mm and 15mm ≤ l2 ≤ 50mm. It is shown that the critical ISSFs at the fracture are constant in the range.12th International Conference on Damage Assessment of Structures 10–12 July 2017, Kitakyushu, Japa

Fatigue Limit Reliability Analysis for Notched Material with Some Kinds of Dense Inhomogeneities Using Fracture Mechanics

This study proposes a quantitative method for predicting fatigue limit reliability of a notched metal containing inhomogeneities. Since the fatigue fracture origin of the notched metal cannot be determined in advance because of stress nonuniformity, randomly distributed particles, and scatter of a matrix, it is difficult to predict the fatigue limit. The present method utilizes a stress-strength model incorporating the “statistical hardness characteristics of a matrix under small indentation loads” and the “statistical hardness characteristics required for non-propagation of fatigue cracks from microstructural defects”. The notch root is subdivided into small elements to eliminate the stress nonuniformity. The fatigue limit reliability is predicted by unifying the survival rates of the elements obtained by the stress-strength model according to the weakest link model. The method is applied to notched specimens of aluminum cast alloy JIS AC4B-T6 containing eutectic Si, Fe compounds and porosity. The fatigue strength reliability at 107 cycles, which corresponds to the fatigue limit reliability, is predicted. The fatigue limits of notch root radius ρ = 2, 1, 0.3, and 0.1 mm are obtained by rotating-bending fatigue tests. It is shown that the fatigue limits predicted by the present method are in good agreement with the experimental ones

Examination on a Criterion for a Debonding Fracture of Single Lap Joints from the Intensity of Singular Stress Field

In this study, the experimental adhesive strength is newly considered in terms of the singular stress appearing at the end of interface between the adhesive and adherent. Here the critical intensity of singular stress field is examined as the debonding criterion for all types of single lap joints under different adhesive thickness and overlap length. The intensity of singular stress can be evaluated by the application of the finite element method focusing on the stress value at the end element of the interface. It should be noted that except for the case of small overlap length the separation always occurs at the edge of the interface causing unstable growth and final brittle fracture. In this type of fracture it is found that the critical intensity of the stress singular field is constant independent of the adhesive thickness and overlap length.13th International Conference on Fracture, June 16–21, 2013, Beijing, Chin

Examination on a Criterion for a Debonding Fracture of Single Lap Joints from the Intensity of Singular Stress Field

13th International Conference on Fracture, June 16–21, 2013, Beijing, ChinaIn this study, the experimental adhesive strength is newly considered in terms of the singular stress appearing at the end of interface between the adhesive and adherent. Here the critical intensity of singular stress field is examined as the debonding criterion for all types of single lap joints under different adhesive thickness and overlap length. The intensity of singular stress can be evaluated by the application of the finite element method focusing on the stress value at the end element of the interface. It should be noted that except for the case of small overlap length the separation always occurs at the edge of the interface causing unstable growth and final brittle fracture. In this type of fracture it is found that the critical intensity of the stress singular field is constant independent of the adhesive thickness and overlap length

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

Analysis of intensity of singular stress field for single lap joint under tensile shear load based on crack tip stress method

In this paper, the crack tip stress method (CTSM) is extended so that the intensity of the singular stress field of the single lap joint (SLJ) with two real stress singularity orders can be analyzed. Two types of the reference models are proposed; one is the tensile force model; the other one is the shear force model. The intensities of the singular stress field of the SLJ are calculated by superposing those of the reference models. The intensities of the singular stress fields of the reference models are calculated by the reciprocal work contour integral method (RWCIM). Then the validity of the reference models and the accuracy of the present method are discussed by comparing the present results with the solutions which are calculated by the RWCIM.3rd International Conference on Fracture Fatigue and Wear, FFW2014, Kitakyushu, Japan, 1-3 September 201

Debonding criterion based on the intensity of singular stress

In the previous study, the authors discussed a debonding fracture criterion for single lap joints(SLJs) with varying the adhesive thickness and overlap length in terms of the critical intensity of a singular stress field. Here it is simply assumed that the identical singular stress fields are formed at the edge corner of the SLJ for different geometries. In this paper, by applying the reciprocal work contour integral method (RWCIM) it is shown that the two distinct intensities of the singular stress fields are determined accurately when the orders of stress singularity are two different real numbers. It is found that the ratio of the intensities of two types of the singular stress fields is almost the same for the wide range of the adhesive thickness and the overlap length. Then, it is found that the debonding fracture criterion is represented in terms of the intensity of the singular stress field with the strong stress singularity when aluminum alloy is bonded by epoxy resin.Proceedings of the 2nd International Symposium on Engineering Mechanics and its Applications, Kitakyushu, Japan, 30 – 31 August 201

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

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

Analysis on intensity of singular stress for bonded pipe in comparison with bonded plate

In our previous research, the intensity of singular stress at the end of interface for bonded platewas discussed under arbitrary material combinations. Also, it was found that the bonded strength of buttjoint can be evaluated in terms of the singular stress in good accuracy. In this study, the intensity of singular stress for bonded pipe is newly discussed in comparison with the one of bonded plate. The finite element method is applied to calculate the intensity of singular stress with varying the material combinationsystematically. This method focuses on the result of first node, which locates on the end of the interface.Since few studies are available for bonded pipe, in this study, first, the singular stress field at the end of the interface of the bonded pipe is investigated under several boundary conditions. Next, the effect of the material combination on the intensity of singular stress is discussed. This investigation may contribute to a better understanding of the debonding strength and initial interfacial cracks of bonded pipe.3rd International Conference on Fracture Fatigue and Wear, EEW2014, Kitakyushu, Japan, 1-3 September 201