3D FE delamination induced damage analyses of adhesive bonded lap shear joints made with curved laminated FRP composite panels

This paper deals with the evaluation of inter-laminar stresses in the adhesive layer existing between the lap and the strap adherends of lap shear joints (LSJ) made with curved laminated fibre reinforced plastic (FRP) composite panels for varied embedded delaminations between the first and second plies of the strap adherend. Non-linear finite element analyses have been carried out using contact and multi point constraint (MPC) elements. The use of contact elements ensures avoidance of inter-penetration of delaminated surfaces. Sequential release of MPC elements facilitates computation of individual modes of Strain Energy Release Rates (SERR). The effects of varied delamination lengths on variations of peel and inter-laminar shear stresses and different modes of SERR are seen to be very significant. Their variations on both the delamination fronts, for each size of the delamination, are found to be much different from each other indicating different propagation rates at the two delamination fronts. The structural integrity of the LSJ in the presence of delaminations, thus, can be predicted with adaptive finite element (FE) simulations. It is further seen that the peak stress magnitudes and SERRs are higher in the LSJs made with curved FRP composite panels as compared to the flat laminates. This may be due to the stiffening effects induced by the curvature geometry of the curved composite panels.     

载重子午线轮胎胎圈疲劳分析

利用Abaqus软件建立子午线轮胎的三维有限元模型,对胎体帘布反包端部裂纹扩展过程进行数值模拟.采用虚拟裂纹闭合技术计算裂纹扩展的应变能释放率,并对裂纹扩展寿命进行计算.研究结果表明,所建立的轮胎裂纹模型能有效地对轮胎胎圈疲劳破坏行为进行描述,并能较好地预测轮胎的疲劳寿命.     

Failure load prediction of structural adhesive joints : Part 2: Experimental study

The objective of this study was to determine how the fracture of adhesive joints depends on elastic beam parameters describing the adherends and the applied loads. The basic specimen geometry was the cracked lap shear joint constructed of aluminium alloy with various adherend and bondline thicknesses. Loads were applied in different combinations of bending, tension and shear to generate a failure envelope for each adhesive and specimen geometry. It was found that crack propagation for precracked specimens occured at a critical strain energy release rate but was also a function of the G_I/G_II ratio and the bondline thickness. The experiments also showed that the loads required to propagate a crack in a precracked specimen were always lower than the loads required to break the fillet. Hence, by treating uncracked joints as being cracked, where the fictitious crack tip is assumed to coincide with the location of the fillet, a conservative estimate of the failure load is obtained.     

Effect of FRP Pipe Scaling on its Adhesive Bonding Strength

Polymer-based materials are emerging as a potential substitute for metallic structures in the oil and gas industry. In this context, fiber-reinforced polymer (FRP) piping is one promising application. An important area of the research pertaining to FRP piping is the connection of pipe sections. Challenges associated with the joining of FRP tubular sections are often considerable, which limits more widespread industrial application. Adhesive bonding is emerging as a promising technique to join tubular FRP structures. The ability to maintain undamaged fiber architecture is a major advantage of adhesive bonding technology. In the present study a strength-of-materials as well as fracture mechanics approach was employed in conjunction with the finite element method to investigate the scaling effects on adhesively bonded tubular sections. It was found that the scaling effects in joined FRP pipe may be significant. For certain composite material configurations the analysis indicated a shift of the region of failure from the pipe structure to pure adhesive (cohesive) failure with increasing pipe diameter.     

Si3N4/BN复合材料界面应变能释放速率的测试与表征

提出了一种更为合理、简便地测试与表征Si3N4／BN复合材料界面应变能释放速率的方法,借助流延成形和热压烧结工艺,制备出具有单一界面层“三期治”结构,在单侧基体中点处预制有裂纹源的Si3N4／BN／Si3N试样,用四点结弯曲加载的方法测出其载荷－位移曲线,进一步求出界面的应变能释放速率值,分别测出了BN＋Si3N4,BN Al2O3两种界面体系、不同成分界面的应变能释放速率值,对于纯BN,含积分数分别为15％,25％Si3N4调节的界面,其相应的应变能释放速率值分别为37．16,90．58,117．76J／m^2;含体积分数分别为16％,36％,63％Al2O3调节剂的界面,临界应变能释放速率值分别为53．95,71．86,119．21J／m^3,试验结果证明了该种方法的可行性及可靠性,与文献所报道的方法进行了对比、分析,同时分析了相关因素对实验结果的影响。     

Relationship between residual stress and strength of single lap joints made of Ti6Al4V alloy,adhesively bonded and treated using pneumatic ball peening

The possibility of improving the strength of single lap joints (SLJs) made of Ti6Al4V alloys and adhesively bonded using Araldite 2014-1 with the help of pneumatic ball peening was investigated. The effects of pneumatic ball peening conditions on the joint strength and residual stress of the plates were determined using mathematical models, i.e. second-degree polynomials. A clear correlation was observed between the joint strength and the post-machining residual stress. Moreover, the stress values could be controlled. Pneumatic ball peening was found to be an easy and effective method for improving the joint strength (up to 57%) of SLJs.     

Observations on Finger-like Crack Growth at a Urethane Acrylate/Glass Interface

Interfacial crack growth behavior along a urethane acrylate/glass interface is characterized by the development of finger-like perturbations along the advancing crack front. The finger-like perturbations grow from a slightly irregular crack front until they reach a steady-state where the velocity of the finger tips equals the velocity of the finger valleys. Once the fingers reached steady-state, the crack velocity was dependent on the applied strain energy release rate via a power law relationship where the exponent was independent of test humidity; however, the multiplicative constant A decreased by an order of magnitude from 80 to 15% RH. The spacing of the fingers was found to be independent of the crack's velocity and the relative humidity of the environment.     

Particle Cleaning of EUV Reticles

The practical adhesion, characterized by either ultimate parameters (F _max or d _max) or the critical strain energy release rate (G _Ic) using the three-point flexure test (ISO 14679-1997), and the residual stress (σ ) profiles within systems of organic layers made of DGEBA epoxy monomer and IPDA diamine hardener were determined. The prepolymer (DGEBA-IPDA) was deposited as thin and thick coatings onto degreased or chemically etched aluminum alloy (5754). To understand the role of the interphase, either a tri-layer (bulk coating/interphase/substrate) or a bi-layer model (bulk coating/substrate) were used for quantitative determination of the critical strain energy release rate. Indeed, as the interphase formation results from both dissolution and diffusion phenomena, we were able to control the interphase formation within coated systems by controlling the liquid-solid contact time and then to make tri- or bi-layered systems. In the three-point flexure test used to determine the practical adhesion, the failure may be regarded as a special case of crack propagation. The model considers residual stresses developed within the entire system leading to an intrinsic parameter representing the practical adhesion between the polymer and the metallic substrate. Moreover, to determine the profiles of residual stresses generated in such systems, the Young's modulus gradient of the interphase was also considered. The maxima in residual stress intensities were found at the interphase/substrate interface for a tri-layer system and at the coating/substrate interface for a bilayer system leading for all systems to an adhesional (interfacial) failure as experimentally observed. A comparison between the results obtained from the three-point flexure test and the Tapered Double Cantilever Beam (TDCB) was made. The determination of the critical strain energy release rate shows that residual stresses cannot be neglected. G _Ic depends on the substrate surface treatment when the residual stresses were neglected. Moreover, we have determined the role of the interphase formation on the practical adhesion before and after hydrothermal aging. The results obtained emphasize that the epoxy/metal interphase affects significantly the initial practical adhesion. However, organo-metallic complex formation improves considerably the hydrothermal durability, as these complexes act as corrosion inhibitors.     

Observations on Finger-like Crack Growth at a Urethane Acrylate/Glass Interface

Interfacial crack growth behavior along a urethane acrylate/glass interface is characterized by the development of finger-like perturbations along the advancing crack front. The finger-like perturbations grow from a slightly irregular crack front until they reach a steady-state where the velocity of the finger tips equals the velocity of the finger valleys. Once the fingers reached steady-state, the crack velocity was dependent on the applied strain energy release rate via a power law relationship where the exponent was independent of test humidity; however, the multiplicative constant A decreased by an order of magnitude from 80 to 15% RH. The spacing of the fingers was found to be independent of the crack′s velocity and the relative humidity of the environment.     

Failure load prediction of structural adhesive joints Part 1: Analytical method

This paper describes an analytical method for calculating the strain energy release rate of cracked adhesive joints. The calculations proceed from a knowledge of the reactions in the adherends at the end of the joint overlap. For joints with equal adherends, a simple method exists for determining the Mode I and Mode II components of the energy release rate. The equations make it relatively easy to apply fracture mechanics failure criteria to arbitrarily loaded adhesive joints. In a subsequent paper, it is shown that by treating uncracked joints as having a crack, with the crack tip coinciding with the location of the spew fillet, the load required to propagate a crack in a cracked joint serves as a reliable conservative estimate of the load required to propagate a crack in an uncracked joint. The present method is suitable, therefore, for failure load predictions of structural adhesive joints in design applications.     

Effect of Bondline Thickness on Mixed-Mode Debonding of Adhesive Joints to Electroprimed Steel Surfaces

Structural applications of adhesive bonding have been increasing in recent years due to improvements in the types of adhesives available and in improved knowledge of bonding procedures. Consequently, there exists a demand for techniques to assess adhesive joint strength, particularly along bondline interfaces where compliant adhesives contact more rigid metallic surfaces. The present study investigates the mixed-mode response of cracked-lap-shear (CLS) joints bonded with unprimed and electroprimed steel adherend surfaces. Three bondline thicknesses, representative of structural automotive joints, were evaluated for unprimed and primed bondlines. Experimental results for static load versus debond extension were input to finite element analyses for computing debond parameters (strain energy release rates). The debonds always initiated at a through-the-thickness location that had the greatest peel component of strain energy release rate. The total strain energy release rate values correlated well with trends in joint strength as a function of bondline thickness.     

Application of a new constant G load-jig to creep crack growth in adhesive joints

A novel constant energy release rate load-jig, capable of applying loads in the full range of mode mixes from pure mode I to pure mode II, was developed for studying creep crack growth in structural adhesive joints. Since the load-jig applies only pure bending moments to uniform double cantilever beam (DCB) specimens, the expressions for the energy release rate and mode ratio are both simple and accurate. The new load-jig was used to study mixed-mode creep crack growth in DCB specimens which had either an intact fillet or a steady-state failure zone. Both a rubber-toughened and a mineral-filled epoxy adhesive were tested at room temperature, which is far below the glass transition temperature for either structural adhesive. In all cases, crack speeds were observed to decelerate, indicating that the adhesive were self-toughening over time. In addition, crack growth was observed to propagate by the initiation and coalescence of microcracks, rather than by the continuous advancement of a crack tip.     

Failure analysis of adhesively bonded tubular joints of laminated FRP composites subjected to combined internal pressure and torsional loading

Abstract

Finite element analysis has been carried in the present research to study individual and combined effect of internal pressure and torsional loading on stress and failure characteristics in case of an adhesively bonded Tubular Single Lap Joints (TSLJ) made of laminated Fiber reinforced polymer (FRP) composite materials. Effect of changing torsional load magnitude on an internally pressurised adhesively bonded TSLJ on interlaminar stresses and onset of different joint fracture modes (adhesion and cohesion failures) has also been studied in the present analysis. Three dimensional stress analysis of the adhesively bonded TSLJ has been carried out through suitable ANSYS Parametric Design Language (APDL) of ANSYS 14.0. Tsai-Wu coupled stress criterion has been used for predicting the onset of joint failures in the TSLJ. It has been observed that stresses (σ_r, σ_θ, σ_z, τ_rz) induced within the joint region under pure internal pressure loading are least affected through introduction of a torsional loading in the TSLJ. However, the stresses (τ_rθ and τ_θz) which are considered to be significant under pure torsional loading get tremendously enhanced due to the varying torsional loading. The interface between the outer tube and adhesive of the TSLJ has been observed to be the most critical bondline interface which is prone to undergo adhesion failure towards the free edges under pure internal loading conditions. However, under pure torsional loading conditions it tends to fracture through adhesion failure towards the clamped edge of the TSLJ. Under combined torsional and internal pressure loading the joint fails towards the clamped edge of the along the critical path which happens to be within the bondline interface, indicating predominance of torsional loading over the pure internal pressure loading. A comparative study based on the magnitude of failure index revealed that torsional loading marginally affects the joint failure as the internal pressure loading improves the compactness of the bonded joint hence improving the resistance of the TSLJ against initiation of joint fractures.     

Optimal Design of the Adhesively-Bonded Tubular Single Lap Joint

In this paper, a method for the optimal design of the adhesively-bonded tubular single lap joint was proposed based on the failure model of the adhesively-bonded tubular single lap joint. The failure model incorporated the nonlinear mechanical behavior of the adhesive as well as the different failure modes in which the adhesive failure mode changed from bulk shear failure, via transient failure, to interfacial failure between the adhesive and the adherend, according to the magnitudes of the residual thermal stresses induced by fabrication.

The effects of the design parameters for the adhesively-bonded tubular single lap joint, such as the thicknesses of adhesive layer and adherends, the bonding length, and the scarfs of adherends, on the torque transmission capability and the efficiency of the adhesive joint were investigated.     

Moisture-assisted crack propagation at polymer/glass interfaces

Moisture-assisted crack growth at various polymer/glass interfaces was measured as a function of applied strain energy release rate and relative humidity using a four-point flexure apparatus coupled with an inverted microscope. The specimens consisted of two glass plates bonded together with a thin layer of commercially available epoxy-acrylate, urethane-acrylate or epoxy adhesive. The crack front at the epoxy-acrylate and epoxy interfaces was relatively smooth and, above a threshold strain energy release rate, the crack growth rate was dependent on the applied strain energy release rate via a power law relationship. Crack growth along the urethane-acrylate interface was characterized by the development of finger-like perturbations along the advancing crack front. These finger-like perturbations grew until they reached a steady-state length. Once the fingers reached steady-state, the crack growth rate of the overallcrack front was dependent on the applied strain energy release rate via a power law function. With all the polymer adhesives crack growth rates increased with higher relative humidities.     

Optimal Design of the Adhesively-Bonded Tubular Single Lap Joint

In this paper, a method for the optimal design of the adhesively-bonded tubular single lap joint was proposed based on the failure model of the adhesively-bonded tubular single lap joint. The failure model incorporated the nonlinear mechanical behavior of the adhesive as well as the different failure modes in which the adhesive failure mode changed from bulk shear failure, via transient failure, to interfacial failure between the adhesive and the adherend, according to the magnitudes of the residual thermal stresses induced by fabrication.

The effects of the design parameters for the adhesively-bonded tubular single lap joint, such as the thicknesses of adhesive layer and adherends, the bonding length, and the scarfs of adherends, on the torque transmission capability and the efficiency of the adhesive joint were investigated.