Browsing by Author "Zhang, Xiang"
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Item Open Access Buckling and post-buckling of a composite C-section with cutout and flange reinforcement(Elsevier, 2013-12-31) Guo, Shijun J.; Li, Daochun; Zhang, Xiang; Xiang, JinwuThis paper presents an investigation into the effect of cutout and flange reinforcement on the buckling and post-buckling behaviour of a carbon/epoxy composite C-section structure. The C-section having a cutout in the web is clamped at one end and subjected to a shear load at the other free end. Three different stiffener reinforcements were investigated in finite element analysis by using MSC Nastran. Buckling load was predicted by using both linear and nonlinear FE analysis. Experiments were carried out to validate the numerical model and results. Subsequently post-buckling analysis was carried out by predicting the load–deflection response of the C-section beam in nonlinear analysis. Tsai-Wu failure criterion was used to detect the first-play-failure load. The effect of circular and diamond cutout shape and effective flange reinforcements were investigated. The results show that the cutout and reinforcement have little effect on the buckling stability. However an L-shape stiffener to reinforce the C-section flange can improve the critical failure load by 20.9%.Item Open Access A cohesive zone model for predicting delamination suppression in z-pin reinforced laminates(Elsevier Science B.V., Amsterdam., 2011-11-14T00:00:00Z) Bianchi, Francesco; Zhang, XiangThis paper presents a cohesive zone model based finite element analysis of delamination resistance of z-pin reinforced double cantilever beam (DCB). The main difference between this and existing cohesive zone models is that each z- pin bridging force is governed by a traction-separation law derived from a meso- mechanical model of the pin pullout process, which is independent of the fracture toughness of unreinforced laminate. Therefore, two different traction- separation laws are used: one representing the toughness of unreinforced laminate and the other the enhanced delamination toughness owing to the pin bridging action. This approach can account for the large scale bridging effect and avoid using concentrated pin forces, thus removing the mesh dependency and permitting more accurate analysis solution. Computations were performed using a simplified unit strip model. Predicted delamination growth and load vs. displacement relation are in excellent agreement with the prediction by a complete model, and both models are in good agreement with test measured load vs. displacement relation. For a pinned DCB specimen, the unit strip model can reduce the computing time by 85%.Item Open Access Criticality of porosity defects on the fatigue performance of wire + arc additive manufactured titanium alloy(Elsevier, 2019-01-28) Biswal, Romali; Zhang, Xiang; Syed, Abdul Khadar; Awd, Mustafa; Ding, Jialuo; Walther, Frank; Williams, Stewart W.This study was aimed at investigating the effect of internal porosity on the fatigue strength of wire + arc additive manufactured titanium alloy (WAAM Ti-6Al-4V). Unlike similar titanium alloys built by the powder bed fusion processes, WAAM Ti-6Al-4V seldom contains gas pores. However, feedstock may get contaminated that may cause pores of considerable size in the built materials. Two types of specimens were tested: (1) control group without porosity referred to as reference specimens; (2) designed porosity group using contaminated wires to build the specimen gauge section, referred to as porosity specimens. Test results have shown that static strength of the two groups was comparable, but the elongation in porosity group was reduced by 60% and its fatigue strength was 33% lower than the control group. The stress intensity factor range of the crack initiating pore calculated by Murakami’s approach has provided good correlation with the fatigue life. The kink point on the data fitting curve corresponds well with the threshold value of the stress intensity factor range found in the literature. For predicting the fatigue limit, a modified Kitagawa-Takahashi diagram was proposed consisting of three regions depending on porosity size. Critical pore diameter was found to be about 100 µm.Item Open Access Damage Tolerance and Fail Safety of Welded Aircraft Wing Panels(American Inst of Aeronautics and Astronautics, 2005-07-01T00:00:00Z) Zhang, Xiang; Li, YazhiAn investigation is presented on fatigue crack growth behavior and fail safety of integral stringer panels typified by welded aircraft fabrications. The stringer panel is made of aluminum alloy 2024-T351 and fabricated by the variable-polarity plasma-arc welding process. The sample simulates a part of the lower-wing skin structures. Based on the linear elastic fracture mechanics, numerical simulations are performed for two configurations, two-stringer and nine-stringer panels, and three damage scenarios, in which welding-induced longitudinal residual stresses are taken into account. A typical load spectrum for large transport aircraft is employed for the analysis. For the two-stringer panel life predictions have a reasonably good correlation with the test results. Based on this validation, large-scale nine-stringer panels with three manufacture options, that is, riveted, integrally machined, and welded integral, are simulated for a skin crack under a broken central stringer propagating to two-bay length. Useful comparisons are made among the three variants. Finally, remedies to improve damage tolerance and fail safety of integral stringer panels are explored. The incorporation of crack retarder straps bonded to the inner surface of an integral panel has greatly improved the fail safety behavior of the component with dramatically increased crack growth live.Item Open Access Damage tolerant wing-fuselage integration structural design applicable to future BWB transport aircraft(Cranfield University, 2009-12) Sodzi, P.; Zhang, XiangWing joint design is one of the most critical areas in aircraft structures. Efficient and damage tolerant wing-fuselage integration structure, applicable to the next generation of transport aircraft, will facilitate the realisation of the benefits offered by new aircraft concepts. The Blended Wing Body (BWB) aircraft concept represents a potential revolution in subsonic transport efficiency for large airplanes. Studies have shown the BWB to be superior to conventional airframes in all key measures. Apart from the aerodynamic advantages, the BWB aircraft also provides a platform for wing-fuselage design changes. The main objective of this research is to design a damage tolerant wing-fuselage joint with a novel bird’s mouth termination for a BWB aircraft that has a similar payload range to the B767 aircraft. The damage tolerance analysis of the proposed BWB wing/fuselage integration structure includes assessments of fatigue crack growth life, residual strength and inspection capability. The proposed structure includes a bird’s mouth termination of the spars that facilitates smooth transfer of loading from the spar web into the root rib and the upper and lower skins and is novel in its application to the blended wing body configuration. A finite element analysis was required to determine local stresses for the prediction of fatigue crack growth life, residual strength and inspection capability and to identify weak spots in the proposed structure. The project aircraft wing comprises of three spars (front, centre and rear) and a false rear spar thus defining a four cell wing box. Wing root shear, bending moment and torque loads were derived and applied to a thin-walled three box idealisation of the proposed structure. The challenges experienced in replicating the loads obtained from the three box idealisation were addressed by modification of the boundary conditions. Checks for compression and shear buckling were also undertaken that confirmed that the applied loads were below the limits of the proposed structure. The finite element analysis showed very clearly that the stresses in the novel bird’s mouth spar termination were significantly lower than in the skin and that the skin remained the more critical damage tolerant component at the wing root when the structure was subjected to ultimate design stresses. The spar web at the bird’s mouth termination was shown to have a larger crack growth life compared to the skin. The thickness of the skin requires further investigation as a significant amount of local bending was experienced due to the applied pressure. The skin will sustain a two-bay crack at the design limit load thus proving the proposed wing fuselage integration structure to be damage tolerant. In conclusion, the main objective of the thesis has been achieved. An integrated wingfuselage joint with novel bird’s mouth spar termination and surrounding structure have been designed and substantiated (evaluated) by damage tolerance requirements.Item Open Access Data: Fatigue crack growth behavior in an aluminum alloy Al–Mg–0.3Sc produced by wire based directed energy deposition process(Cranfield University, 2023-08-04 15:41) Ye, Jin; Khadar Syed, Abdul; Zhang, Xiang; Eimer, Eloise; Williams, StewartAdditive manufacturing (AM) of Al-Mg-Sc alloys has received considerable interest from the aerospace industry owing to their high specific strength and suitability for AM. Since damage tolerance is a mandatory requirement for safety critical aerospace structures, this study has investigated the fatigue crack growth behaviour in an Al-Mg-0.3Sc alloy made by the wire and arc additive manufacturing. Tests were conducted with two different crack orientations at load ratios 0.1 and 0.5. At the lower load ratio and lower stress intensity factor range (10 MPa m1/2, isotropic crack growth rate property was measured; grain size effect was overcome by the mechanical factor (the stress intensity factor). At the higher load ratio 0.5, both the threshold and the critical values of the stress intensity factor range were reduced. Finally, the modified Hartman-Schijve equation was successfully employed to represent the crack growth rates including the threshold and the fast crack growth regions.Item Open Access Design and analysis of welded aircraft wing panels(Cranfield University, 2005-12-05) Theos, Athanasios; Zhang, XiangNowadays, increasing manufacturing cost effectiveness becomes a vital condition for the commercial success of the next generation of large wide body aircrafts. Welding is a very strong candidate process to be used in manufacturing, allowing both sensible cost reductions and structural efficiency. The main aim of the work is to study the fatigue crack propagation in welded structures. The study is focused on the effect of welding residual stresses to the damage tolerance behaviour of the structure. The welding technique under investigation is the Variable Polarity Plasma Arc (VPPA). Two stringer panels were designed, one tension panel to simulate the lower wing skin cover and one compression panel to mimic the upper wing skin cover. The main design driving force for the upper stiffened panel is buckling since it is under compression. Damage tolerance is the main design criterion for the lower stiffened panel due tensile fatigue loading. Design of the end- fittings for the tension stiffened panel was also carried out using finite element modelling in order to ensure uniform stress distribution at the cross section of the test area of the structure. A fatigue analysis at the various locations of the bolts and at the weld line has been performed. This is necessary in order to ensure that the crack initiation site comes from the weld line rather than from the fastener holes at the end-fittings during the fatigue testing. The research was focused on fatigue crack growth behaviour of welded aluminium panels. The FE model of the CCT coupon is the main tool for the comparison of the fatigue crack behaviour between the parent and the welded coupons. Furthermore AFGROW software is used in conjuction with the output of the FE model to compare the experimental and numerical results in terms of fatigue crack growth lives of welded coupons. In welded coupons a faster crack propagation growth was demonstrated at the region of the weld line and the heat affected zone (HAZ) due to the tensile welding residual stresses. Away from this region, a decrease in crack growth took place due to the compressive welding residual stresses in this area. Finally, a calculation effort in large-scale stiffened panels was made in terms of the stress intensity factor for both welded and non-welded cases. Possible future work was also addressed in such large-scale structures.Item Open Access Design and Modeling of Selective Reinforcements for Integral Aircraft Structures(American Inst of Aeronautics and Astronautics, 2008-09-01T00:00:00Z) Boscolo, M.; Allegri, Giuliano; Zhang, XiangA numerical simulation is presented in this paper on the performance of crack retarders bonded to integral metallic structures. The work is described in two main parts. First, a novel modeling approach employing the finite element method has been developed for simulating the various failure mechanisms of a bonded structure and for predicting fatigue crack growth life. Crack growth in the substrate and the substrate/strap interface disbond failure are modeled in the framework of linear elastic fracture mechanics. A computer code interfacing with the commercial package MSC NASTRAN has been developed and validated by experimental tests. Second, the effectiveness of different strap configurations on crack growth retardation has been modeled; these include different strap materials, strap dimensions, and their locations on the substrate. The research has included two substrate materials and four strap materials, and at this stage the specimens were cured at room temperature. Strap stiffness and adhesive toughness are found to be the most influential parameters in designing crack retarders. A design tool has been developed based on the numerical simulation to achieve optimal crack retarder design in terms of prescribed fatigue life target and minimum structural weight added by the bonded reinforcement.Item Open Access Design and numerical modeling of a pressurized airframe bulkhead joint(American Institute of Aeronautics and Astronautics, 2015-11-01) Giannopoulos, Ioannis K.; Theotokoglou, Efstathios E.; Zhang, XiangThe structural loading on a conceptual lap joint in the empennage of a civil aircraft has been investigated. The lap joint interfaces the end-pressure part-hemispherical bulkhead to the cylindrical fuselage. The pressure bulkhead is made of carbon fiber reinforced plastic materials. The aim of the study is to present numerical results of the induced structural loading from the fuselage positive internal pressure differential and the localized high stress intensity field at the lap joint location. A methodology for the appropriate numerical approach to analyze the domed pressure bulkhead is presented. The results of the numerical investigation showed that the laminate loading levels calculated by the use of either initial sizing analytical formulas for pressurized domes or by the use of equilibrium nodal loading from finite element models of low fidelity compared to refined finite element analysis can be significantly underestimated. Some of the implications on carbon fiber reinforced plastic structural sizing at the specified location are developed.Item Open Access Effect of rolling on fatigue crack growth rate of Wire and Arc Additive Manufacture (WAAM) processed Titanium(Cranfield University, 2013-11) Qiu, Xundong; Zhang, XiangTitanium (Ti) alloys have been commonly used in the aerospace industry, not only because they have a high strength-to-weight ratio (comparing to the steels) but also their satisfactory corrosion resistance. Furthermore, they can be assembled with the carbon fibre composite parts. However, conventional manufacturing methods cause high material scrap rate and require lots of machining to obtain the final shape and size, which increases both the manufacturing time and cost. In order to improve the efficiency and reduce the cost of Ti parts, Additive Manufacturing (AM) has been developed. Rolled Wire and Arc Additive Manufacturing (rolled WAAM) is one of the AM processes. The main characteristics of this technology is the reduced β grain size to refine the alloy's microstructure. Both the ultimate tensile strength and yield strength of Ti alloy made by rolled WAAM are at least 10% higher than traditional wrought Ti. This project is to investigate the fatigue crack growth rates of the Ti-6Al-4V built by rolled WAAM process in both the longitudinal and transverse orientations to study the effect of rolling on fatigue crack growth rate of WAAM processed Ti. The project was carried out by testing the fatigue crack growth rates for 4 compact tension specimens. The test results of different orientations were compared with each other, and scatters in fatigue life and fatigue crack growth rate were found. Fatigue crack growth rate is lower in the longitudinal specimens. The results are also compared with those of the unrolled WAAM specimens tested in a previous project. It was found that rolling can significantly improve the fatigue crack growth behaviour in WAAM processed Ti, and can reduce the difference between the two orientations, i.e. achieving better isotropic material properties. Recorded scatters may be caused by the process induced residual stresses, error in measurement, and the test machine load range being much higher than the applied loads. More specimens can be tested to validate above observations further.Item Open Access Evaluating stress intensity factors due to weld residual stresses by the weight function and finite element methods(Elsevier Science B.V., Amsterdam., 2010-09-30T00:00:00Z) Bao, Rui; Zhang, Xiang; Yahaya, N. A.This paper presents a study on the application of the weight function and finite element methods to evaluate residual stress intensity factors in welded test samples. Three specimen geometries and various residual stress profiles were studied. Comparisons of the two different methods were made in terms of the accuracy, easiness to use, conditions and limitations. Calculated residual stress intensity factors by the two different methods are in general in good agreement for all the configurations studied. Computational issues involved in executing these methods are discussed. Some practical issues are also addressed, e.g. treatment of incomplete or limited residual stress measurements, influence of transverse residual stresses, and modelling residual stress in short-length specimens. The finite element method is validated by well-established weight functions and thus can be applied to complex geometries following the procedures recommended in this paper. (C) 2010 Elsevier Ltd. All rights reserved.Item Open Access Evaluation of the intrinsic crack growth rates of weld joints(Elsevier Science B.V., Amsterdam., 2011-04-30T00:00:00Z) Zhang, Xiang; Bao, RuiA method is presented for evaluating weld intrinsic fatigue crack growth rate (FCGR) by excluding the influence of residual stresses. The method is potentially useful for predicting crack growth lives of structural components using measured FCGR data from coupon specimens. Calculation procedures are developed and demonstrated via an example of crack growth across a longitudinal weld subjected to both constant amplitude loading and constant applied stress intensity factor ranges. Trends of intrinsic FCGR in different weld regions are identified. The methodology can also be used for establishing intrinsic FCGR laws for cracks propagating within and parallel with the weld joint.Item Open Access Experimental and numerical study of process-induced defects and their effect on fatigue debonding in composite joints(Elsevier, 2019-03-22) Liu, Yiding; Zhang, Xiang; Lemanski, Stuart; Yazdani Nezhad, Hamed; Ayre, DavidLaboratory coupon joints for fatigue debonding tests usually have narrow width and a through-width initial disbond. However, realistic structural joints are much wider and may contain process-induced defects and accidental damage; both are much smaller than the joint width. Small and discrete damage may behave differently from the idealised through-width disbond crack. This has brought a question on whether the laboratory coupon joint can accurately represent the fatigue behaviour of wider structural joints. This paper presents an experimental and numerical study of fatigue behaviour of a wide bonded lap joint with a process-induced defect of semi-circular shape. Fatigue debonding propagation was monitored by ultrasound inspection. Fatigue life was predicted using a normalised strain energy release rate parameter calculated by finite element method, and the adhesive material fatigue crack growth rate data measured under single and mixed mode conditions. Simulation of process-induced defect and validation by experiments have brought a better understanding of fatigue debonding behaviour in wide joints containing realistic damage. Suggestions are given for fatigue fracture tests of bonded joints.Item Open Access Fail-Safe Design of Integral Metallic Aircraft Structures Reinforced by Bonded Crack Retarders(Elsevier Science B.V., Amsterdam., 2009-01-01T00:00:00Z) Zhang, Xiang; Boscolo, M.; Figueroa-Gordon, Douglas J.; Allegri, Giuliano; Irving, Phil E.This paper presents an investigation on the effectiveness of crack growth retarders bonded to integral metallic structures. The study was performed by both numerical modelling and experimental tests. It focuses on aluminium alloy panels reinforced by bonded straps made of carbon-epoxy, glass-epoxy composite materials or a titanium alloy. The goal was to develop a fail-safe design for integrally stiffened skin-stringer panels applicable to aircraft wing structures. The modelling strategy and finite element models are presented and discussed. The requirements that the models should meet are also discussed. The study has focused on establishing the extent of crack retarder benefits, in terms of fatigue crack growth life improvement, by numerical simulation and experimental tests of various crack retarders. The results of predicted fatigue crack growth retardation have been validated by tests of laboratory samples. This study concludes that by bonding discrete straps to an integral structure, the fatigue crack growth life can be significantly improved.Item Open Access Fatigue crack growth behaviour and life prediction for 2324-T39 and 7050-T7451 aluminium alloys under truncated load spectra(Elsevier Science B.V., Amsterdam., 2010-07-01T00:00:00Z) Bao, Rui; Zhang, XiangThis paper presents a study of crack growth behaviour in aluminium alloys 2324- T39 and 7050-T7451 subjected to flight-by-flight load spectra at different low- stress truncation levels. Crack branching was observed in the higher truncation levels for the 2324 and in all truncation levels for the 7050. Mode I crack growth life can be predicted for the 2324 alloy by the NASGRO equation and the Generalised Willenborg retardation model. However, quantitative prediction of the fatigue life of a significantly branched crack is still a problem. Material properties, test sample’s orientation and applied stress intensity factor range all play dominant roles in the fracture procesItem Open Access Fatigue crack growth in additive manufactured titanium: residual stress control and life evaluation method development(VTT Information Service, 2017-06-09) Zhang, Xiang; Martina, Filomeno; Syed, Abdul Khadar; Wang, Xueyuan; Ding, Jialuo; Williams, Stewart W.This paper presents fatigue crack growth behaviour in titanium alloy Ti-6Al-4V built by the Wire + Arc Additive Manufacture (WAAM®) process. Process induced residual stress and stress relief by cold working were measured by neutron diffraction and contour methods. Residual stress retained in the compact tension test specimens was evaluated by the finite element method based on the measured stresses in the WAAM wall. Fatigue crack growth rate in as-built and stress relieved conditions are discussed with respect of the effects of material build orientation, residual stress, and microstructure characteristics. Key conclusions are: (a) residual stresses arising from the WAAM process can be controlled and reduced significantly by cold working. Residual stress retained in compact tension specimens is low, resulting in low residual stress intensity factor. (b) Microstructure affects fatigue crack growth rate in twodifferent material’s build orientations. (c) Fatigue crack growth rate in WAAM Ti-6Al-4V is lower than that in traditional wrought plate, with and without the residual stress relief. Therefore, WAAM is a viable additive manufacture process to produce aerospace titanium alloys for damage tolerance design.Item Open Access Fatigue life improvement in fatigue-aged fastener holes using the cold expansion technique(Elsevier Science B.V., Amsterdam., 2003-09-01T00:00:00Z) Zhang, Xiang; Wang, Z.The use of cold expansion process as a life extension technique on aircraft structural joints was investigated. The primary focus was an experimental test programme consisting of open-hole and low-load transfer joint specimens made of 2024-T351 aluminium alloy and pre-fatigued to 25, 50 and 75% of the baseline fatigue life for plain holes. The FALSTAFF loading spectrum was applied. The results indicate that significant life improvements can be obtained through cold expansion applied at all percentages of fatigue life tested in this work with the optimum stage being around 25% of the baseline life. The major life extension was obtained through slower crack growth in the short crack stage. The life improvement factors for the open-hole and joint specimens were comparable provided that the degree of cold expansion is the same. Crack growth life of the open-hole specimen was predicted by employing an analytical residual stress model and the AFGROW computer code. The prediction results showed good agreement with the experimental results for cold expansion at build cases.Item Open Access Fatigue life prediction of z-fibre pinned composite laminate under mode I loading(Elsevier, 2019-02-13) Tang, Suchao; Lemanski, Stuart; Zhang, Xiang; Ayre, DavidA hybrid method is presented combining linear elastic fracture mechanics with nonlinear damage mechanics that can predict the fatigue crack growth rate in z-fibre pinned composites under mode I loading. The strain energy release rate is evaluated using the virtual crack closure technique via finite element analysis. Cohesive elements are used in the pinned region to represent the crack bridging force generated by the pins. The reduction of the pins' bridging force under the fatigue loading is accommodated by applying a degradation law, based on damage mechanics with empirical fitting parameters. A modified degradation law is proposed which is capable of accumulating fatigue damage under varying crack opening displacement ranges experienced by the pins during fatigue loading. Fatigue testing was performed with a z-pinned double cantilever beam at two different values of applied displacement amplitude. The predictions show reasonably good agreement with the test results in terms of the fatigue crack propagation rate and fatigue life.Item Open Access Finite element analysis of bonded crack retarders for integral aircraft structures(Cranfield University, 2009-04) Boscolo, M.; Zhang, XiangTrends in aircraft design and manufacture are towards the reduction of manufacturing cost and structural weight while maintaining high level of safety. These reductions can be achieved by using integral structures. However, integral structures lack redundant structural members, hence fail safety is not guaranteed. Bonded selective reinforcements (straps) can obviate this problem and improve the damage tolerance capability of integral structures, although increase the design di±culties. The objective of this research is to develop an effective analysis method to predict the fatigue crack growth (FCG) life of integral structures reinforced by bonded crack retarders, determine the effectiveness of the reinforcements, and assess the important strap design parameters. The main mechanisms that influence the crack propagation have been identified, modelled, and discussed. When a crack propagates in the panel skin, bonded straps delay the fracture growth by exerting bridging forces at the crack tip. Nevertheless damage also affects the strap due to the stiffness mismatch and high stress concentration, and the strap/substrate interface is affected by a progressive delamination that advances together with the substrate crack and limits the strap bridging action. Tensile thermal residual stresses (TRS) in the cracked substrate, caused by the adhesive cure process, act to open the crack and hence increase the growth rate. Last but not least, secondary bending caused by the non-symmetric configurations induces a stress gradient along the crack front. This reduces the effectiveness of the bridging action and causes a curved crack front. An enhanced 2D FE modelling technique that takes into account of these mechanisms and their interactions has been developed and implemented in a computerprogram that interfaces the commercial code NASTRAN. This program is used to calculate the stress intensity factors and the FCG life of bonded strap reinforced integral structures. This modelling technique has been validated for a wide range of test samples in terms of TRS and their redistribution with crack propagation, disbond areas, and FCG lives. The FCG life of a large scale integral skin-stringer panel reinforced by various bonded straps has also been predicted and compared with the experiments. Numerical predictions have shown good agreement with the experimental measurements. Parametric studies have been conducted to understand the effectiveness of different strap configurations on crack growth retardation; these include different strap materials, strap dimensions and locations on the substrate. A design tool has been developed aimed at achieving optimal crack retarder design in terms of prescribed fatigue life target and minimum structural weight. In conclusion, a novel modelling tool has been developed, the effectiveness of bonded straps in retarding fatigue crack growth has been demonstrated and, following the parametric analysis, the most important parameters in the design of bonded straps have been identified.Item Open Access A finite element model for predicting the static strength of a composite hybrid joint with reinforcement pins(MDPI, 2023-04-22) Bianchi, Francesco; Liu, Yiding; Joesbury, Adam M.; Ayre, David; Zhang, XiangThis paper presents a finite element model for predicting the performance and failure behaviour of a hybrid joint assembling fibrous composites to a metal part with reinforcement micro pins for enhancing the damage tolerance performance. A unit-strip model using the cohesive elements at the bond interface is employed to simulate the onset and propagation of debonding cracks. Two different traction–separation laws for the interface cohesive elements are employed, representing the fracture toughness properties of the plain adhesive bond and a pin-reinforced interface, respectively. This approach can account for the large-scale crack-bridging effect of the pins. It avoids using concentrated pin forces in the numerical model, thus removing mesh-size dependency, and permitting more accurate and robust computational analysis. Lap joints reinforced with various pin arrays were tested under quasi-static load. Predicted load versus applied displacement relations are in good agreement with the test results, especially for the debonding onset and early stage of crack propagation.