CERES :: Browsing by Author "Ghasemnejad, Hessam"

Browsing by Author "Ghasemnejad, Hessam"

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Open Access
Advancement in design and failure analysis of aluminium foam-filled honeycomb crash absorbers
(Springer, 2023-03-01) Valente, Goncalo; Ghasemnejad, Hessam; Srimanosaowapak, S.; Watson, James W.
Honeycomb structures are frequently used as energy absorption devices in the automotive and aerospace industry. Many studies have been conducted to optimise these structures and improve crashworthiness behaviour. This paper attempts to improve the crashworthiness behaviour of a honeycomb crash box by filling the cells with open-cell aluminium foams. Experimental tests were conducted to develop the honeycomb and aluminium foam material model and, also, to validate the finite element model by experimental data. The finite element model was developed in ABAQUS, and different variables were parameterised to aim a quick implementation. The empty aluminium honeycomb crash box is used as a term of comparison with the foam-filled ones. Foam-filling the crash box allows the control of the densification zone for different impact energies using open-cell aluminium foam, which shows the main novelty of this research. In the end, the optimised structure is presented concerning the optimum number of foam-filled cells and, also, to the aluminium foam’s density that best fits this application.
Open Access
Aluminium foam-filled honeycomb crash absorbers
(Trans Tech Publications, 2023-04-06) Valente, Goncalo; Ghasemnejad, Hessam; Srimanosaowapa, Sompong
Honeycomb structures are frequently used as energy absorption devices in the automotive and aerospace industry. Many studies have been conducted to optimise these structures and improve crashworthiness behaviour. This paper attempts to improve the crashworthiness behaviour of a honeycomb crash box by filling the cells with open-cell aluminium foams. Experimental tests were conducted to develop the honeycomb and aluminium foam material model and, also, to validate the finite element model by experimental data. Foam-filling the crash box allows the control of the densification zone for different impact energies using open-cell aluminium foam, which shows the main novelty of this research. In the end, the optimised structure is presented concerning the optimum number of foam-filled cells and, also, to the aluminium foam’s density that best fits this application.
Open Access
Analysis of the effect of impact damage on the repairability of CFRP composite laminates.
(2017-02) Alzeanidi, Nasser; Ghasemnejad, Hessam
Polymer composite materials are common in the aerospace application such as aircraft structures including primary and secondary structures. Therefore, there has been an increasing demand for composites in both the military and civilian aircraft industry. At least 50% of the next generation of military and civil aircraft structures are likely to be made from composites. The most important properties for composite materials in aircraft application was the high strength-to-weight ratios, stiffness-to-weight ratios and easy to repair. However, the composite materials have low resistance for impact damage. Impact can lead to significant strength reduction in aircraft structure about 40% to 60% of an undamaged composite laminate strength. Therefore, establish a numerical methodology to defined the optimum repair joint to restore sufficient strength of damaged aircraft composite structures during some operations and exercise activities with limited resources which will be the main contributions to knowledge in this thesis. To achieve this contribution need to understanding of the behaviour of Carbon Fibre Reinforced Plastic (CFRP) composite laminates subject to high velocity impact and the unrepaired composite laminates and repaired (stepped joint) subject to compression after impact test. Therefore, this study consists of two parts:- first, part a combined of numerical simulation and experimental investigation have been used to evaluate the woven CFRP laminate subject high velocity impact. The selected impact velocities were (140m/s, 183m/s, 200m/s, 225m/s, 226m/s, 236m/s, 270m/s, 305m/s, 354m/s and 368m/s) in order to evaluate the induced impact damage in three different thickness of CFRP composite laminates (6 mm, 4.125 mm and 2.625 mm) these velocities were selected according the gas gun limitation. The woven composite laminate made of Hexcel G0926 Carbon Fabric 5 harness 6K, Areal Weight 370 gsm. The resin used was Hexcel RTM 6, cured for 1 hour 40 minutes at 180° C at a pressure of 100 psi, with an average thickness of 0.375mm. The laminates were comprised of 16 layers, using the following stacking sequence: [(0/90); (±45); (±45); (0/90); (±45); (±45); (0/90); (0/90); (±45); (0/90); (±45); (0/90); (±45); (0/90); (±450); (0/90)], 11 layers, using the following stacking sequence: 0/90; ± 45; 0/90; ± 45; 0/90; ±45; 0/90; ± 45; 0/90; ±45; 0/90 and 7 layers, using the following stacking sequence: ± 45; 0/90; 0/90; ±45; 0/90; 0/90; ±45. The density of woven CFRP laminates was 1.512e-3 ±1e-6 grm/mmÖ³. The penetration process and also change of kinetic energy absorption characteristics have been used to validate the finite element results. The experimental and numerical method in this study show a significant damage occurs, including delamination, compression through thickness failure, out-of-plane shear failure and in-plane tensile failure of the fibres located at the rear surface when the projectile penetrates the laminate. The penetration mechanism of the projectile had a “plugging-type” (shear) failure and the hole that was formed after impact was conical in shape were shown in experimental and also verified in the numerical model. The residual kinetic energy in numerical model is 5.0 % larger than experimental data which is significantly matched in all simulated cases. In part two a finite element model is established to optimise the repair joint to restore sufficient strength of damaged composite laminate and used compression after impact test to compare the compression failure load of the sample. In order to achieve this an optimised repair models of stepped lap joints with variable parameters such as number of steps and length of steps have been experiment the undamaged composite laminate and composite laminate subject to high velocity impact and also created a numerical model for these experimental. The experimental CAI failure load of undamaged 7 Plies CFRP composite laminate higher than the failure load of damaged specimens by approximately 23%. The undamaged 11 Plies CFRP composite laminate failed at approximately 40% higher than the damaged specimens. Moreover, the difference between the experimental and numerical results of above tests was about 10%. The numerical model of repaired composite laminate show the damage initiated at the end of overlap and the average compression failure load of the stepped lap joint increased with the increasing of the number of step and length of step. The 85% and 90% of compressive failure load has been restored.
Open Access
Analytical development on impact behaviour of composite sandwich laminates by differentiated loading regimes
(Elsevier, 2022-06-02) Chao Correas, A.; Ghasemnejad, Hessam
Given the widespread usage of composite components in critical structures within the aerospace and automotive industries, it is deemed as an essential task to determine the effect of normal operation phenomena on its performance in impact. In particular, the present study aims for providing the developed analytical modelling techniques which are needed for describing the low velocity impact dynamic response of sandwich laminated structures. Alongside the analytical models, experimentally validated high-fidelity numerical models are used to check both the validity of the assumptions made as well as the accuracy of the analytical results in the different considered scenarios. An extensive analysis of the sandwich laminate impact performance has been studied, eventually resulting in a much improved, herein developed analytical formulation which is capable of accounting for the differentiated loading, unloading and reloading indentation regimes as well as for the lower facesheet local deflections. These considerations, which are normally neglected in equivalent studies, allow a precise capture of the energy absorption mechanisms.
Open Access
Analytical solutions to predict impact behaviour of stringer stiffened composite aircraft panels
(Springer, 2021-05-25) Chao Correas, A.; Casares Crespo, A.; Ghasemnejad, Hessam; Roshan, G.
This paper aims to develop an analytical method to predict the low-velocity impact response of simply supported stringer stiffened panels. Since the combination of stringer and panel provides aircraft structure with variable thicknesses, significant mathematical modelling is required to predict the transverse impact response of this type of designs. Within this analysis, the effect of variable stiffness distribution due to the stringer presence has been included. The performance of various layups is investigated to find the most suitable combination for panel-stringer laminate under impact loading. Analytical models were developed based on a spring-mass system to predict the dynamic behaviour of the striker-plate domain and, finally, determine the contact force history, which shows the main novelty of this research. Compared with Finite Element results, the model developed proved to successfully predict stringer stiffened composite panels' response with a range of layups and geometry designs under low-velocity impact loading conditions. The analytical results agree with the available data in the literature, and the error is less than 5%.
Open Access
Crashworthiness of foam-filled and reinforced honeycomb crash absorbers in transverse direction
(Springer, 2023-11-29) Nicoud, G.; Ghasemnejad, Hessam; Srimanosaowapak, S.; Watson, J. W.
Honeycomb crash absorbers have been widely studied as energy absorption devices for use in automotive industries. However, none of these investigations have studied the side impact of empty and foam-filled honeycomb absorbers and adding stiffeners between the different layers of the corrugated sheets which are composing the honeycomb structure to analyse the structure under transverse (L-direction) impacts. In this paper, the foam-filled and reinforced honeycomb crash absorbers are investigated under axial (T) and transverse (L) loading directions. Experimental results for both empty and foam-filled specimens under quasi-static and impact loads were implemented to validate the developed finite element model. Finite element analysis (FEA) was performed to find out the crashworthiness behaviour of the structure under axial and transverse impacts according to road conditions. Finally, a new design of stiffened honeycomb crash absorber was developed and investigated to reduce the level of acceleration experienced by the passengers during the crash event. In this regard, it is concluded that all the requirements related to the energy absorption capabilities and generated deceleration under impact loading can be met by introducing an advanced method to reinforce honeycomb absorbers using stiffeners. It is also proven that the thickness of these stiffeners will not significantly influence the force levels. Due to increase of wall thickness from 1 to 3 mm, the mean crushing force increased from 129 kN to 148 kN. This growth is not sufficient as the goal is to obtain a mean crushing force of 300 kN. Thickening the stiffeners would lead to a loss of efficiency of the structure, as the small increase in mean force would not make up for the gain in mass. Thus, increasing the corrugated sheet’ thickness becomes necessary.
Open Access
Developed trigger mechanisms to improve crush force efficiency of aluminium tubes
(Elsevier, 2019-09-11) Rai, V.; Ghasemnejad, Hessam; Watson, James W.; Gonzalez-Domingo, J. A.; Webb, Phil
This paper aims to investigate the effect of a trigger mechanism on the crush force efficiency of aluminium tubular absorbers. Various trigger mechanisms such as cut-out holes, circumferential notch and end-fillet, were studied using the validated numerical model. Initially, tubes made of aluminium displayed better crashworthiness behaviour when compared with steel tubes based on numerical and experimental results. Then the trigger mechanism consisting of three cut-out holes was found more efficient than the ones with an end fillet and a circumferential notch based on a comparative study. According to these results, the developed trigger mechanisms have a significant change in crashworthiness performance of tubular absorbers. Crush force efficiency was doubled with the help of this trigger mechanism while stroke efficiency and specific energy absorptions were reduced by 4% and 15% respectively.
Open Access
Development of a CFRTP manufacturing method to improve low velocity impact resistance of aerospace structures.
(Cranfield University, 2020-08) Delporte, Yoan; Ghasemnejad, Hessam; Webb, Phil
A continuous carbon fiber reinforced Polymer was manufactured using a Fused Deposition Modelling method. Current Fused Deposition Modelling machine are not able to manufacture Carbon Fiber Reinforced Thermoplastic Polymer composite therefore modification and novel designs needed to be made and integrated to the Fused Deposition Modelling machine to achieve a final product. To investigate the benefits of our composite a comparison with available composites on the market composed of similar materials needed to be performed. We investigated the different aspect of the requirements needed to manufacture test samples. We focused on manufacturing method able to integrate continuous Carbon Fiber simultaneously to a thermoplastic. In the slicing software a custom g code sequence has been developed to forward the continuous Carbon Fiber through the Bowden tube to the hotend. This procedure allowed the hotend to move freely between the layup of the printed part. Also C code library has been developed to analyse the geometry of the part to recognise the amount of Carbon Fiber, which needs to be pushed through the Bowden tube connected to the hotend. We investigated the mechanical properties as well as the process parameters of the individual materials used to manufacture our Carbon Fiber Reinforced Thermoplastic Polymer samples. In addition Carbon Fiber Reinforced Thermoplastic low velocity impact samples have been produced to investigate the potential of our composite in comparison to available products on the marker like Short Carbon Fiber Polyamide filaments. The low velocity performances of the Continuous Carbon Fiber Thermoplastic Polymer samples have been promising compared to conventional Short Carbon Fiber Polyamide samples. The advantages of using an Fused Deposition Modelling machine to manufacture composites is the ease to choose between numerous fiber orientations, which a significantly important feature for impact applications. In addition a potential case study for aerospace structure applications of our Carbon Fiber Reinforced Thermoplastic Polymer will be investigated and discussed. The novelty behind this is research is in the coding sequence allowing the fiber cutting system to trigger a the a specific moment in order to integrate the necessary amount of fiber according to the distance of the hotend travelled on the heat bed. Another novelty is in the unique servo actuated fiber cutting system using a specific cutting mechanism. The contribution to the knowledge is the study of the behaviour of a thermoplastic composite under low velocity impact. To investigate the effect of process parameters on a thermoplastic composite. To develop a novel cutting system and code control. Vibration cancellation method for even and continuous integration of continuous carbon fiber cutting method for precise carbon fiber cutting and integration to thermoplastic via Bowden extrusion system. Coding for the motherboard firmware as well as G code for the slicer have been optimised in order to produce quality samples. The effect of hardware on process parameters have been investigated though tensile tests. Low velocity impact performance of continuous carbon fiber polyamide has been also investigated and tested.
Open Access
Development of multi aluminium foam-filled crash box systems to improve crashworthiness performance of road Service vehicle
(Elsevier, 2025-01) De Biasio, Antony; Ghasemnejad, Hessam; Srimanosaowapak, S; Watson, JW
Honeycomb crash absorbers are known as mechanical energy-absorbing systems in both automotive and aerospace industries. However, the gap of knowledge in the transverse impacts of multi-foam-filled or stiffener-reinforced honeycombs is still unfilled. This paper investigates the energy absorption process in large crash boxes applied onto a road maintenance vehicle, exploring four aluminium honeycomb absorbers with design factors like added aluminium foam, corrugated sheet thicknesses, and stiffener reinforcements. The optimised foam-filled honeycomb structures are analysed for four crash scenarios in two different directions; frontal impact (T-direction) and lateral impact (L-direction) subjected to 50 km/h crash speed. The objective of this research is to identify the most efficient design that achieves a maximum acceleration of up to 20g while absorbing a specific energy of 145 kJ. The FE models were developed in ABAQUS to explore various scenarios related to damage zones, impact energy capabilities, and multi-foam-filled crash boxes. Finally, the lightest design of honeycomb absorbers which can maximise energy absorption while maintaining acceleration below the specified threshold of 20g will be recommended.
Open Access
Effect of bird-strike on sandwich composite aircraft wing leading edge
(Elsevier, 2020-06-15) Arachchige, B.; Ghasemnejad, Hessam; Yasaee, Mehdi
In this paper, a parametric numerical study is performed on the sandwich composite leading edge to analyse the effect of skin thickness, layups, impact velocities to compare the performance of the two different reinforcements within sandwich leading-edge structures. The detailed numerical analysis of a composite leading edge reinforced with honeycomb and foam is developed using explicit finite element software, LS-DYNA. Initially, the study proposes the most suitable equations of state for impact on the metallic leading edge for different bird geometries made from Lagrangian and SPH methods. All the numerical results are verified with available experimental data in the literature. The results will deliver a cost-efficient and accurate numerical model which assists aircraft designers in deciding the combination of design variables resulting in improved impact resistance for sandwich aircraft structures under soft body impacts.
Open Access
Effect of variable core stiffness on the impact response of curved sandwich plates
(Elsevier, 2018-06-02) Arachchige, B.; Ghasemnejad, Hessam
An extensive analytical model to determine behaviour of curved sandwich plates with variable stiffness cores and face-sheets under low velocity impact with foam core is presented in this paper. A developed method is introduced to determine effective dynamic stiffness of the face-sheets and core with variable stiffness. A modified spring-mass-dashpot model was used to obtain the contact force function related to effective dynamic stiffness and effective dynamic frequency to determine the contact force histories by impact of a hemispherical-nose impactor. A parametric study was also performed to understand the effects of several factors such as impactor velocity, face-sheet thickness, core thickness (constant and variable stiffness), layup orientation and curvature on the contact force histories of curved sandwich plates. Different geometries of curved sandwich plates are analysed to study their performance under impact loading. Numerical analysis was performed in LS-DYNA to further validate with the developed analytical models.
Open Access
Experimental and numerical investigation of multi-layered honeycomb sandwich composites for impact mechanics applications
(Elsevier, 2024-02-01) Al Ali, A.; Arhore, Edore G.; Ghasemnejad, Hessam; Yasaee, Mehdi
This project aims to investigate the design of a multi-layered sandwich composite and its performance under impact loading conditions. An experimental and numerical assessment was performed to conclude the effect of increasing the layers of sandwich panels. Three specimens of four different sandwich panel configurations were manufactured to be tested. The skin of the sandwich panels comprises a twill carbon-reinforced epoxy resin, whereas the core consists of a 2D Nomex honeycomb core. The panels are then subjected to transverse impact loading to investigate their impact behaviour. These experimental results are then used to verify numerical models constructed in LS-Dyna. The models of the honeycomb-reinforced sandwich panels are investigated using MAT-054 and MAT-142 material cards in LS-Dyna to find the most economical computational approach. Finally, the energy absorption characteristics calculated during the experimental and numerical work are used to conclude the multi-layered sandwich composite's performance and provide design recommendations. The findings suggest that by increasing the core and shell numbers through the thickness of the panel, the specific energy absorption capability will increase.
Open Access
Finite element modelling approach for progressive crushing of composite tubular absorbers in LS-DYNA: review and findings
(MDPI, 2021-12-29) Rabiee, Ali; Ghasemnejad, Hessam
Robust finite element models are utilised for their ability to predict simple to complex mechanical behaviour under certain conditions at a very low cost compared to experimental studies, as this reduces the need for physical prototypes while allowing for the optimisation of components. In this paper, various parameters in finite element techniques were reviewed to simulate the crushing behaviour of glass/epoxy tubes with different material models, mesh sizes, failure trigger mechanisms, element formulation, contact definitions, single and various numbers of shells and delamination modelling. Six different modelling approaches, namely, a single-layer approach and a multi-layer approach, were employed with 2, 3, 4, 6, and 12 shells. In experimental studies, 12 plies were used to fabricate a 3 mm wall thickness GFRP specimen, and the numerical results were compared with experimental data. This was achieved by carefully calibrating the values of certain parameters used in defining the above parameters to predict the behaviour and energy absorption response of the finite element model against initial failure peak load (stiffness) and the mean crushing force. In each case, the results were compared with each other, including experimental and computational costs. The decision was made from an engineering point of view, which means compromising accuracy for computational efficiency. The aim is to develop an FEM that can predict energy absorption capability with a higher level of accuracy, around 5% error, than the experimental studies.
Open Access
Identification of the key design inputs for the FEM-based preliminary sizing and mass estimation of a civil aircraft wing box structure
(Elsevier, 2021-12-14) You, Chao; Yasaee, Mehdi; He, Shun; Yang, Daqing; Xu, Yigeng; Dayyani, Iman; Ghasemnejad, Hessam; Guo, Shijun; Webb, Phil; Jennings, James; Federico, Giovanni
FEM-based preliminary structural sizing has been successfully carried out for a typical single-aisle wing box structure using MSC Nastran, by considering various load cases representing typical aircraft manoeuvres, engine loads, landing and ground handling conditions. The strength, buckling and fatigue criteria have been applied as the design constraints for sizing. The resultant total mass and the structural (static and modal) behaviour of the sized wing box model have been verified against a validated high-fidelity wing box model. A sensitivity analysis has been performed to evaluate the influence of the number of design fields and the selected design inputs (i.e. load cases and design constraints) on the accuracy of sizing and mass estimation of the wing box. This sensitivity analysis has also been extended to the static and modal behaviour of the wing box structure obtained from sizing. It provides an insight into the significance of considering the buckling and fatigue constraints, aircraft rolling loads, engine loads and landing loads in sizing, in addition to the commonly-applied 2.5 g aircraft pull-up loads under the strength constraint. The findings of this study highlight the trade-off between the sizing efficiency and accuracy of a civil aircraft wing for modelling purposes.
Open Access
Improvement of force history pattern in composite tubular structures by developed trigger mechanisms
(Springer, 2022-06-14) de la Cuesta, J. J.; Ghasemnejad, Hessam
This paper investigates the effect of various trigger mechanisms on the force history pattern, initial collapse load, mean force and specific energy absorption of CFRP composite tubular absorbers. These trigger mechanisms are bevel with angles of 15°, 30°, 45° and 60° and tulip with angles of 60° and 90° and tip numbers of 4 and 6. Experimental studies were performed for three trigger mechanisms of Bevel (B30° and B60°) and tulip with four tips and angle of 60°, 4T60. It was shown that tulip mechanisms significantly change the force–displacement pattern in comparison with bevel triggers. In this case, the initial collapse load decreases, which leads to improving the crush force efficiency (CFE) and progressive energy absorption. This analysis also contains numerical modelling, which investigates other designs of bevel and tulip trigger mechanisms with different angles. Finally, numerical results are validated against experimental results using advanced finite element techniques in LS-Dyna. The developed tulip trigger mechanisms indicated a significant change of crushing force history, which results in improvement of crashworthiness parameters.
Open Access
Improvement of specific energy absorption of composite tubular absorbers using various stitching pattern designs
(Springer, 2020-11-26) Rabiee, Ali; Ghasemnejad, Hessam
In this paper, various patterns of multi-stitched locations were studied experimentally and numerically to improve the specific energy absorption (SEA) in composite tubular absorbers. In this regard, stitching patterns with a horizontal distance of 3 mm, 6 mm, 9 mm and 18 mm in straight and zig-zag designs were investigated to justify their effect on mean crushing force and energy absorption capability. A multi-shell configuration finite element model is also developed based on energy-based contact definitions, which considers the delamination in Mode-I and stitching pattern design to accurately predict the energy absorption capability and axial crushing behaviour of composite crash absorbers, At stitched locations, the critical normal surface separation was utilised concerning experimental data to improve delamination resistance. The multi-stitching rows of 10–15-20–25-30–35 mm with 3 mm horizontal and 2.5 mm vertical distances between each stitched point can increase the specific energy absorption up to 32% in comparison with non-stitched specimens. The developed numerical model for multi-layered composites absorbers in comparison with the existing methods is efficient in terms of accuracy with less than 5% error in comparison with experimental data.
Open Access
Investigation of energy absorption of a GFRP composite crash box
(WIT Press, 2008) Ghasemnejad, Hessam; Hadavinia, H; Aboutorabi, A
Interlaminar fracture toughness of composite materials plays an important role on the specific energy absorption (SEA) of the crushing of composite materials. In this regard an optimum composite crash box design is sought by studying the effect of fibre orientation and stacking sequence on the increase of interlaminar fracture toughness. In order to achieve this, various glass fibre/epoxy orientations were studied experimentally. Double Cantilever Beam (DCB) and axial crush box specimens were made and tested in a quasi-static condition to determine the interlaminar fracture toughness (GIC) and SEA values for each set of fibre orientation and stacking sequence. The effect of the stacking sequence on fracture toughness and the SEA of the GFRP composite crash box has been quantified and optimum results were obtained.
Open Access
Laminate tailoring of composite tubular structures to improve crashworthiness design at off-axis loading
(Scientific Research Publishing, 2018-07-10) Rabiee, Ali; Ghasemnejad, Hessam
This paper presents experimental and numerical investigation on the parameters effecting energy absorption capability of composite tubular structures at oblique loading to improve crashworthiness performance. Various inclined angles of 5˚, 10˚, 20˚ and 30˚ were selected for the study of off-axis loading. The results indicate that by increasing the lateral inclination angle the mean crushing force and also energy absorption capability of all tested sections decreased. From design perspective, it is necessary to investigate the parameters effecting this phenomenon. The off-axis loading effect that causes significant reduction in energy absorption was investigated and the effected parameters were improved to increase energy absorption capability. To establish this study, 10˚ off-axis loading was chosen to illustrate the obtained improvement in energy absorption capability. Five cases were studied with combinations of ply-orientation and flat trimming with 45˚ chamfer. This method was applied to the integrated 10˚ off-axis loading and the final results showed significant improvement in energy absorption capability of composite absorbers. Finite element model (FEM) was developed to simulate the crushing process of axial and off-axis composite section in LS-DYNA and the results were in good agreement with the experimental data.
Open Access
Lightweight design of multi-stitched composite crash absorbers to improve specific energy absorption capability under quasi-static and impact loading
(2018-05) Rabiee, Ali; Ghasemnejad, Hessam
A comprehensive numerical and experimental study was performed to investigate the energy absorbing capabilities of glass/epoxy and carbon/epoxy members that could serve as stanchions in the subfloor structure of aircraft or rotorcraft. Circular cross sections with chamfered-ends failure trigger mechanism were investigated under axial and off-axis loading conditions. The optimal configuration that resulted in the highest possible specific energy absorption (SEA) was identified, which was at axial loading. The parameters in off-axis loading conditions that affected energy absorption capability were identified. Several cases were experimentally studied to cancel off-axis (oblique) loading effect. To increase interlaminar fracture toughness, stitching through the thickness was considered. Single, multi and pattern-stitching were studied to increase energy absorption capability of GFRP composite sections. The failure mechanisms, crushing process and force-displacement curve diagram of each case was studied to establish the effect of stitching on energy absorption capability. A correlation between stitching location and localised and global increase of energy absorption was established. It was identified, that the closer the stitching locations are, the higher the localised peak load becomes, and it influences the Mode-I crack propagation (main central crack) resistance, bending of fronds and friction, consequently, pattern-stitching resulted in a 15% increase in specific energy absorption capability (SEA) under quasi-static loading. Similarly, this stitching pattern resulted in a 14% increase in SEA using CFRP sections. Under impact loading, it was identified that pattern-stitching through the thickness resulted into 17% and 18% increase in SEA using GFRP and CFRP sections, respectively. Finite element models were also developed to simulate the crushing behaviour of the CFRP and GFRP sections observed experimentally under axial, off-axis, quasi-static and impact loading conditions. A multi-layer modelling methodology was developed by determining the most effective element size, number of shells, formulation, contact definitions, delamination interface, material model, friction and trigger mechanism. This approach captured the failure process, predicted the SEA and sustained crush load quite accurately within 5% error. Stitching through the thickness was modelled using an energy-based contact card to implement stitched and non-stitched Mode-I and Mode-II energy release rate parameters. This method accurately predicted stitched composite sections with 3% error compared with experimental data. Such modelling could thus support the future design of aircraft stitched and non-stitched stanchions within reasonable computer efficiency and accuracy.
Open Access
Lightweight design to improve crushing behaviour of multi-stitched composite tubular structures under impact loading
(Elsevier, 2018-11-19) Rabiee, Ali; Ghasemnejad, Hessam
This paper presents experimental and numerical studies on the effect of multi-stitching pattern on the energy absorption capability of composite tubular structures under impact loading. A new multi-stitching pattern was developed to study the increase of specific energy absorption capabilities in GFRP and CFRP crash absorbers. The stitching pattern on both specimens showed a significant increase in energy absorption capability under impact loading. According to our results, the specific energy absorption of GFRP and CFRP composite tubes are 17% and 18% higher than non-stitched specimens respectively. A multi-shell finite element model was constructed to predict the axial crushing behaviour and energy absorption capability of composite structures under impact loading. The method is based on an energy-based contact card modelling technique in the stitched and non-stitched area, and the initiation of main central crack growth occurs when the critical separation (PARAM function) is attained, and this represents the functionality of the stitched area during an impact event. The developed numerical approach is efficient in terms of accuracy and simplicity in comparison with the existing methods for multi-layered composites structures.