Characterisation On The Mechanical Properties Of Adhesively Bonded Corrugated Sandwich Structures:an Experimental And Modelling Study

Many industries have an interest in the benefits of adhesives,for example automobile manufacturers,aircraft,railways,ships and construction industries.Recently there have been concerns in regard to lowering the weight of transportation vehicles.Traditional joining methods,such as riveting,bolting,using screws and welding can lead to increases in a vehicle's total structural weight.Conversely,a structural adhesive is frequently utilised for joining dissimilar modern lightweight materials,where a mechanical fasteners and welding are inappropriate to use.Given the advances in adhesive-based industries,adhesively bonded corrugated sandwich structures(ABCSS)may be one solution for the abovementioned industrial sectors.Information regarding the ABCSS mechanical properties is harder to find in the literature and an area which requires further study.The aim of the research is the investigation of the ABCSS mechanical properties under quasi-static loading conditions with adhesive fillets,curing history and hygrothermal ageing effects and optimisation procedures.To complete these implementations,the objectives are given as follows.First,an adhesive fillet is suggested for improving ABCSS mechanical performance,however,not much research exists which focuses on the effects of adhesive fillets on ABCSS stress states.This study presents an experimental-finite element model which was performed to examine the effects of adhesive fillets on ABCSS mechanical performance under a three-point bending load.Three-point bending tests were performed to verify the model using numerical analytical procedures on the ABCSS.The Cohesive Zone Model(CZM)analysed the damage in both the adhesive layer and the fillets.An increase in fillet size provides more smooth transitions between the adherend and the adhesive layer and therefore reduces stress concentrations at the edges of the overlapping regions.In other words,designing and increasing the fillet size of ABCSS can help providing better internal stress distribution as well as higher load-bearing capacities of it.Secondly,examining the effects of various curing temperatures and duration on the ABCSS using a 3-point bending test evaluates load bearing capacity.Both transverse and longitudinal ABCSS loading directions were built and tested.The chosen curing temperatures and durations of the ABCSS were provided in 3 types of curing histories.Failure strength tests were conducted to determine the adhesive's basic properties with selected curing histories.The bulk tensile,End-Notched Flexure,and Double Cantilever Beam tests were performed for material characterization and to verify the produced numerical analyses.The adhesive's glass transition temperature(Tg)with various curing records were configured through the use of differential scanning calorimetry.Stress distribution and crack propagation in the adhesive layers were replicated via the bilinear traction-separation law of CZM.Critical ultimate load predictions and the equivalent failure modes correlated well with experimental observations.This study reveals that regular step-wise increases in curing temperatures and durations can increase the fracture resistance and mechanical performance strength of the ABCSS.Additionally,adhesive stress state analysis of the ABCSS signifies that the stress concentration becomes severer under higher curing temperatures and duration,based on which the dangerous locations of failure occurrence in the adhesive layer can be revealed.Thirdly,the moisture content on ABCSS mechanical performance was investigated.Amongst commonly occurring ABCSS failure modes,adhesive and cohesive failure happening in the adhesive layers and interfaces are a primary failure mode,which lead to the whole structure being destroyed.The current research constructs a combination numerical-experimental method to characterize ABCSS strength degradations in hostile humid-hot environments.Both a salty and deionised water were under consideration for use as the ABCSS immersion setting.ABCSS mechanical properties were loaded under a 3-point bending test before(unaged)and after(aged)50? at 45 days of immersion.Numerical models were carried out in 2 stages:(1)to characterize the longer-term ageing processes in ABCSS in wet-hot conditions through the use of fully-coupled methodologies,and(2)simulating the remaining strength of the aged ABCSS in quasi-static 3-point bending through use of a degraded CZM with a bilinear traction-separation law.Validation of the suggested ABCSS FE modelling under 3-point bending aged in a humid-hot setting was performed alongside the experimental data,which proves the accuracy and validity of the suggested numerical predictive techniques.Subsequently,discussion was conducted of the failure analysis in the ABCSS in addition to the adhesive layer.Finally,the research analyses of stress distribution and optimisation of the ABCSS subjected to the 3-point bending test.The End-Notched Flexure and Double Cantilever Beam tests were conducted for two adhesive materials characterization.The corresponding experiments were conducted and a comparison was made with the numerical analysis results to determine load-displacement curves.Subsequently,CZM integrated into the simulation was used for obtaining stress distribution at the bonding joint regarding major ABCSS geometric parameters.Moreover,this research considers the optimisation design procedures relating to different geometric parameters on the ABCSS.To optimise the ABCSS layout determined by the design parameters,proposed an integrated process established by multiple software platforms.A design matrix with four geometrical factors and 60 design points were created using the Optimal Latin Hypercube method.Finally,the multi-objective optimisation algorithm for the Pareto front of the optimisation problem was defined and obtained.The designers can then choose the optimal sample points according to the emphasis placed on these two ABCSS types based on the parameters as Load,Displacement and Weight.Additionally,the obtained results show that ABCSS at a longitudinal load direction has better mechanical performance.