Spew Fillet Research Articles

Topology optimization of adhesively bonded double lap joints

Current studies show great, but unutilized potential for mechanical optimization of adhesively bonded joints. There are different approaches, e. g. mixed adhesive joints; tapered adherends or joints with spew fillets, all of which try to redistribute the stress peaks, occurring at the ends of adhesive layer overlap, in favor to the load capacity. However, these investigations fail to take a general approach to find optimal geometric solutions to the problem of joining two materials by means of adhesive bonding. Instead the geometry is changed by predefined parameters such as tapering angles, spew fillet radii or the number of adhesives in mixed adhesive joints. To allow a non-parametric optimization, this paper proposes and investigates an extended bi-directional evolutionary structural optimization methodology based on a failure criterion to account for othotropic materials, which are often used in the context of bonding. The optimized joint geometry, generated by the proposed algorithm, resulted in a fairly constant distribution of elemental failure probability compared to the non-optimized state, thus eliminating underutilized spots of material and increasing the efficiency of the connection. Furthermore the influence of different parameters such as the overlap-length to adherend thickness ratio; the stiffness between adherend and adhesive as well as the adherend degree of orthotropy were investigated for optimal joint geometry.

Numerical design of rotationally molded composite tie rods

Rotational molding constitutes a promising manufacturing technology for rotationally symmetric components made of thermoset matrix with continuous fiber reinforcement. The present study deals with the numerical analysis of a rotationally molded composite tie rod with metallic load introduction elements. For this purpose, the adhesive joint between carbon fiber reinforced plastic and metallic load introduction element was investigated in more detail. Different geometries of a spew fillet were evaluated to reduce the stress peaks occurring at the ends of the overlap. A design of experiments was used to determine the influence of the different parameters. An optimized geometry was derived and compared with a reference in terms of stress distribution. Subsequently, test specimens were rotationally molded and mechanically tested. The results of the study show that the maximum stresses within the adhesive layer can be reduced with an optimized spew fillet, and thus a higher mechanical tensile load of the composite tie rod can be achieved.

Effect of spew fillet on adhesively bonded single lap joints with CFRP and aluminum-alloy immersed in distilled water

The aim of this study was to investigate the effect of a spew fillet on adhesively bonded single lap joints (SLJs) with carbon fiber-reinforced plastic (CFRP) and an aluminum alloy immersed in distilled water. After the SLJs with and without the spew fillet were immersed in distilled water for a specified aging time, the strengths of the SLJs were measured via quasi-static axial tensile experiments, and the strain distribution at the side interface of the adhesive layer in the joints was obtained via digital image correlation (DIC) technology. The tensile test results showed that the strength of the SLJs can be significantly improved by introducing the spew fillet, and the strength of the SLJs decreased as the aging time increased both with and without the fillet. However, compared with the SLJs without the fillet, the strength of the SLJs with the fillet decreased further. The DIC results showed that the main reason for the influence of the fillet on the SLJs was that the fillet enhanced the peel strength and shear strength of the adhesive layer in the overlap area.

Fatigue strength evaluation and fracture behavior of joined dual phase steel/AA6061-T6 aluminum alloy

The fatigue strength evaluation and fracture behavior for a dual phase steel-AA6061-T6 bonded joints with three different adhesives (DC-80, Betamate 120 and MP55420) are presented in this paper. Single lap shear tests were used to determine maximum shear loads, for the single lap shear testing for 5.0 mm overlap length were 2 to 3.5 times higher in comparison to the 12.7 mm overlap length specimens. The results for the strain measurement revealed that higher strain-stress were developed in the 6061-T6 aluminum alloy adherend and in all cases they were lower than the adherends yield strength. Fatigue testing was carried out at 30, 50 and 70 % of the maximum shear load, 0.1 of reversibility load ratio (R) and 30 Hz of frequency. After testing, Basquin and Wholer graphs were built for each adhesive at 12.7 and 50.0 mm of overlap length. The results suggested that at higher overlapping, the cyclic maximum load increased. Additionally, the maximum fatigue loading at 10^6 cycles for MP55420 adhesive was 1.3 kN for an overlapping of 12.7 mm and 2.9 kN for 50 mm. For DC80 adhesive was 1.75 kN for overlapping 12.7 mm and 4.8 kN for 50 mm. Finally, for the Betamate 120 adhesive was 1.8 kN for 12.7 mm of overlapping and 6 kN for 50 mm. The post-fracture visual inspection revealed that MP55420 and Betamate 120 adhesives had a cohesive failure, while the DC-80 showed cohesive-adhesive failure. Additionally, the scanning electron microscopy evaluation on the spew fillet revealed resolved striations and a network of small micro-dimples for the Betamate 120 and MP55420 adhesives. On the other hand, DC-80 adhesive exhibited notable facet fragile failure that was confirmed by the shape of stress-strain plot with straight line from the origin to the point of fracture.

Surface toughening – a concept to decrease stress peaks in bonded joints

ABSTRACTBy using fiber-reinforced plastics as the material for lightweight structures, adhesive bonding becomes an increasingly focused solution for joining these components. In comparison to bolted joints, adhesive bonding has a lot of known benefits, e.g. sealing, no weakening of adherends and a homogeneous load transfer. However, the stress distributions in single-lap joints are not homogeneous all over. Both the shear and peel stress distribution have a peak at the overlap ends of the joint and a lower loaded part in the middle, as shown by Volkersen and Goland and Reissner. In order to reduce these stress concentrations, there are known concepts for the modification of the joint. In this paper, adherend chamfering, different adhesive spew fillet geometries, and the mixed adhesive joint are investigated and compared to a novel local adherend surface toughening concept by using a thermoplastic PVDF layer. A high-resolution digital image correlation is used to visualize the deformation in the bondline. While the state-of-the-art used concepts do not show a high increase of joint strength for single lap joints, the joint strength for the surface toughening specimens can be increased by up to 84%.

Experimental Investigation on Fatigue Behavior of Wide-Flange Steel I-Beams Strengthened Using Different CFRP End Cutting Shapes

In recent decades, the application of carbon fibre-reinforced polymer (CFRP) composites for strengthening structural elements has become an efficient option to meet the increased cyclic loads, or repair due to fatigue cracking. The premature failure due to end-debonding is a key limitation to achieve high fatigue performance of strengthened steel beams with externally bonded CFRP plates. The objective of this study is to explore the reinforcing techniques using the CFRP in-plane end cutting shapes and the triangular spew fillet of adhesive at the tips of the plate to care for fatigue damaged of wide-flange steel I-beams due to end-debonding. Four in-plane CFRP end cutting shapes were chosen, namely: rectangular, semi-elliptical, semi-circular and trapezoidal. The application of the trapezoidal end shape was found to be the best configuration for delaying the end-debonding failure mode and high fatigue life compared to the other CFRP in-plane end cutting shapes. Applying the triangular spew fillets of adhesive significantly increased the end-debonding and steel beam fracture initiation life of the strengthened beams.

Effects of adhesive parameters on out-of-plane compression and compression fatigue response of adhesively bonded sandwiches with pyramidal core

Effects of key adhesive parameters such as curing temperature and the amount of adhesive on the out-of-plane compression and fatigue strength of sandwich panels with pyramidal core are experimentally investigated and compared with those of theoretical analysis. It is shown that two different curing temperatures lead to the different liquidity of surplus adhesive squeezed out and then the shapes of spew fillet. Sandwich panels with arc spew fillets have higher compression strength than those with rounded spew fillets. With the increase of the amount of adhesive, the out-of-plane compression strength of those sandwich panels clearly increases firstly and then gradually tends to the theoretical value. By analysis of the S-N fatigue curves of four types of sandwich specimens, the shape of spew fillet, the amount of adhesive and the loading ratios are identified as the key factors governing the compression fatigue properties of truss-cored sandwich structures.

Strengthening of steel structures with CFRP strips

The paper presents the results of research on the suitability of externally bonded composite strips of carbon fibre-reinforced polymer (CFRP) for post-strengthening of steel structures. Specimens with the strips applied on both sides (double cover joints) were prepared and subjected to axial tension tests to find which of the eight different configurations of end detailing provides the strongest bond. The strengthening effect of externally bonded composite strips was tested on sixteen steel I-beams, including determination of the effective bond length and the effects of the thickness of adhesive layer and modulus of the CFRP strip on the load capacity of the steel-adhesive-CFRP strip assembly. The research showed that externally adhered CFRP strips can increase the bending strength of steel structures (an 8% increase was obtained in the experiments) and the shape of spew fillet can have a significant influence on the strength of the strengthened system (the difference reaching up to 57%).

Effect of adherend recessing on bi-adhesively bonded single-lap joints with spew fillet

The effect of adherend recessing on the strength of full (spew)-fillet-formed bi-adhesively bonded single-lap joint (SLJ) was investigated using the finite-element (FE) method under pure tension (i.e., 20 dissimilar recess length and depth and two-type bi-adhesive bond). A three-dimensional (3D) FE model was developed for bi-adhesively bonded SLJ, which had fillet and recessed adherend, assuming that both adhesive and adherend have geometrical non-linearity and exhibit linear material behaviour. The novelty of present study is the application of recessing process on the fillet-formed bi-adhesively bonded SLJs. The bondline characteristics of bi-adhesively bonded joints with the effect of adherend recessing have been investigated by examining the distributions of the peel and maximum principle stresses (MPS) at the mid-plane of the bondline. The results from the FE simulations in which varying geometric parameters are used reveal that the combined effects of adherend recessing spew fillet and bi-adhesive bondline led to a major decrease in the peak values of the peel stress, which is the governing failure stress and MPS. A novel design that may be beneficial to improve the strength characteristics of aluminium SLJ is presented.

Three-Dimensional Modeling of Single-Lap Joints with Variable Interfacial Crack Length <sup></sup>

This paper investigated the performance of single-lap joints with interfacial crack through the finite element method. The finite element method was validated by the G-R solutions at first. And then the influence of geometric parameter of the joint as well as the length of the interfacial crack were discussed. Results showed that the presence of a spew fillet can reduced the stress intensity factors (SIF).The relationship of the crack length ratio and SIF, adhesive thickness ratio and SIF were built.

An investigation on the effect of parallel slot in bi-adhesive single lap joints with spew fillet

The combined effect of full (spew) fillet formed bi-adhesive and parallel slot in adherend on the stress distribution along the length of adhesive bonded single lap joint (SLJ) was investigated using the finite element (FE) method under pure tension (i.e. twenty parallel slots of dissimilar length and depth and two types of bi-adhesive bonds). The FE model of the joints that had fillet, parallel slot and bi-adhesive bondline was developed. In this study, it is assumed that both adhesive and adherend have geometrical nonlinearity and exhibit linear material behavior. The bondline behavior of bi-adhesively bonded joints has been studied by examining the distributions of the peel and maximum principal stresses at the mid-plane of the bondline. The novelty of this study is to investigate the bondline behavior of fillet formed SLJ with the integration of parallel slot mechanism. The results of the numerical computation show that the combined use of the parallel slot and spew fillet on bi-adhesively bonded lap joint decreased the peak value of the peel and maximum principal stresses markedly. The improvement of the strength properties of the joints has been acquired from the studies in which varying geometric parameters are used. This model may be beneficial to enhance the strength of aluminum SLJ.

한 끝단 형상에 따른 마그네슘 합금과 유리섬유 복합소재 단일겹치기 본드 조인트 거동 분석

본 연구에서는 마그네슘 합금과 유리섬유/에폭시 복합재로 구성된 단일겹치기 조인트의 접착부재의 끝단 형상에 따른 조인트의 구조거동을 시험적으로 평가하였다. 이를 위해 4가지 서로 다른 끝단부 형상을 갖는 마그네슘 합금-유리섬유/에폭시 복합재 단일겹치기 시편을 제작하였다. 또한, 인장 시험을 통해 각 단일겹치기 조인트의 파단 거동을 평가하였다. 시험결과 끝단형상이 직각인 형상을 갖는 조인트의 파단 강도가 가장 낮았다. 이에 반해, 접착부재가 역방향 테이퍼를 갖는 조인트의 접합강도가 가장 높았고, 이 값은 끝단 형상이 직각인 형상 대비 약 11.1% 증가된 접합강도이다. In this study, the strength of magnesium-GFRP/epoxy single-lap bonded joints are experimentally evaluated with different end shapes. In order to achieve this, four different single-lap joints with different end shapes are fabricated and the failure load is measured under tensile loading tests. From the test results, the single-lap joint with a square end exhibits the lowest failure load while the single-lap joint with reverse tapering and a spew fillet has the highest stress values. It has 11.1% higher failure strength than the single-lap joint with a square end.

Effect of the Spew Fillet on Adhesively Bonded Single-Lap Joint Subjected to Tensile Loading: Experimental and 3-D Non-Linear Stress Analysis

In the single-lap joint (SLJ) geometry, peel stresses occur at the overlap ends due to load eccentricity and the presence of shear-free adhesive termination surfaces. These peel stresses, along with the transverse tensile stresses which occur along the overlap longitudinal axes, and adhesive shear stresses, ultimately cause joint failure. Obviously, reductions in these stresses should result in higher joint strength and increased load capacity. In the present study, the mechanical behavior of the SLJ geometry of various widths having spew fillets, which was subjected to tensile loading, were investigated experimentally and numerically. For this purpose, firstly, four different types of SLJ samples (without spew fillet, with spew fillet at joint edges, with spew fillet at joint ends, and with spew fillet at all edges) were produced for experimental studies by using two-part paste adhesive. Then, stress analyses in the SLJ were performed with a three-dimensional non-linear finite element method by considering the geometrical non-linearity and non-linear material behaviors of both adhesive (DP460) and adherend (AA2024-T3). It was concluded that the spew fillet in the SLJ geometry with variable widths decreases stress concentrations and increases the load carrying capacity of the joint.

Optimization of geometry of elastic bodies in the vicinity of singular points on the example of an adhesive lap joint

The stress state in adhesive lap joints with various geometric shapes of spew fillet is studied. It is noted that the applied design models of the considered problem include singular points at which infinite stress values are possible if one uses the linear elasticity theory to calculate the stress state. Based on the conclusions of the solution of the geometry optimization problem in the vicinity of the singular points of elastic bodies, variants of the geometry of spew fillet, which provide the most significant decrease in the concentration of stresses in adhesive lap joints, are proposed.

Analysis and design of adhesively bonded joints for fatigue and fracture loading: a fracture-mechanics approach

An experimental–computational fracture-mechanics approach for the analysis and design of structural adhesive joints under static loading is demonstrated by predicting the ultimate fracture load of cracked lap shear and single lap shear aluminum and steel joints bonded using a highly toughened epoxy adhesive. The predictions are then compared with measured values. The effects of spew fillet, adhesive thickness, and surface roughness on the quasi-static strength of the joints are also discussed. This fracture-mechanics approach is extended to characterize the fatigue threshold and crack growth behavior of a toughened epoxy adhesive system for design purposes. The effects of the mode ratio of loading, adhesive thickness, substrate modulus, spew fillet, and surface roughness on the fatigue threshold and crack growth rates are considered. A finite element model is developed to both explain the experimental results and to predict how a change in an adhesive system affects the fatigue performance of the bonded joint.

The effect of the spew fillet on an adhesively bonded single-lap joint subjected to bending moment

The mechanical behaviors of an adhesively bonded single lap joint with a spew fillet under bending moment, where the widths of the upper-adherend and lower-adherend are not the same, were studied experimentally and numerically. Using AA2024-T3 aluminum alloy as adherend and DP460 as paste adhesive, four different types of single-lap joint samples (without spew fillet, with spew fillet at joint edges, with spew fillet at joint ends and with spew fillet at all edges) were produced for experimental studies. Stress analyses in the single-lap joint were performed with a three dimensional non-linear finite element method by considering the geometrical non-linearity and non-linear material behaviors of both adhesives (DP460) and adherend (AA2024-T3). The single lap joint with the spew fillet with different widths had a significant effect on the stress distribution. Additionally, the spew fillet increased the load carrying capacity of the joint and decreased the stress concentration of the joint.

Progressive Failure Analysis of Adhesively Bonded Laminates Joints with Spew Fillets

Failure prediction of adhesively bonded single-lap laminates joints with spew fillets in the overlap ends under uniaxial tensile loading is performed by progressive failure analysis method. A modified form of Hashins failure criterion by Shokrieh and maximum stress criterion are used to detect the laminate failure and adhesive failure, respectively, where a sudden degradation model is proposed to reduce engineering material constants. Five kinds of failure modes are considered. The numerical analysis of composites adhesive joints is implemented in ANSYS Parametric Design Language (APDL) with commercial finite element codes ANSYS. The error of simulation and experimental failure loads is 6.9% and the model has been validated by comparing numerical results with experimental results.

Stress Distribution in Reverse-Bent Bonded Joint

Adhesively bonding technology is used increasingly by the automotive and aerospace industries. The design of reverse-bent joint is effective way for improving the bonded joint performance. The influence of preformed angle on the stress distribution of the adhesive-adherend interface is studied in this paper using finite element analysis (FEA). By comparing the results of the FEA for reverse-bent joints with different preformed angle, it can be seen that the preformed angle not only have significant influence on the stress distribution of overlap section, but also changes stress concentration at the spew fillet of bonded joint. The results also indicate that there is a best value of preformed angle in which the reverse-bent bonded joint has the best performance.

Three-dimensional modeling of carbon/epoxy to titanium single-lap joints with variable adhesive recess length

The objective of this paper was to investigate the performance of recessed single-lap joints with dissimilar adherends through the finite element method. The influence of material and geometric nonlinearity of the adhesive as well as the impact of the recess length was examined in terms of maximum principal stresses. The strength of the joint was obtained as the load to initiate the crack propagation. Results suggested that either adding a spew fillet or considering the adhesive plasticity led to reduced peak stresses at the edge of the adhesive layer. The presence of a spew fillet in the single-lap joint with a recess length of 50% of the overlap length reduced the peak stress concentrations in the adhesive layer by 45.2% and subsequently improved the strength of the joint by 36.3%. Mitigation of stress concentration was observed in cases of an adhesive layer with a smaller recess length. The strength of recessed joints with a gap less than 50% of the overlap length decreased slightly. For the recess length as 70% and 90% of the total overlap length, the strength of the joints reduced 36.4% and 66.3%, respectively. This study suggested a recess of less than 50% of the overlap length may be beneficial for the performance of the joints.

Influence of Roughness on the Mechanical Adhesion of Single Lap Joints

The single lap joints analysis has been developed from different perspectives, including overlap length, adhesive thickness, spew fillet formation, stress distribution, and manufacturing parameters. This paper describes recent results in the study of the roughness influence on the mechanical adhesion of single lap joints in composite test specimens made of glass fiber with a polymeric matrix. Analysis techniques were based on both finite element and experimental approaches. For the above-explained purpose, two cases were simulated: one with a surface roughness of the adherend in the joint overlap, and another one with a minimal roughness surface in the overlap zone. It was considered that the adhesive behaves like an isotropic material. As for the specimens used in the experimental tests, the surface roughness of the adherends was controlled by using an anti-adhering fabric, and the adherend specimen's surface without roughness was controlled using glass as a mould. The numerical results were validated experimentally by means of tensile tests. In the simulation where substrates with surface roughness were used, it was observed that the maximum shear stress at the joint ends decreases by 21% when compared with the model developed with adherends without roughness. Nevertheless, in the test specimen with roughness, a redistribution of the stresses exists that move from the adhesive to the substrates, which causes an increase of the single lap joint resistance. The same was observed in the experimental tests where an increase of four times in the load supported by the joint was obtained.