Progressive Crushing of Polymer Matrix Composite Tubular Structures: Review

The present paper reviews crushing process of fibre-reinforced polymer (FRPs) composites tubular structures. Working with anisotropic material requires consideration of specific parameter definition in order to tailor a well-engineered composite structure. These parameters include geometry design, strain rate sensitivity, material properties, laminate design, interlaminar fracture toughness and off-axis loading conditions which are reviewed in this paper to create a comprehensive data base for researchers, engineers and scientists in the field. Each of these parameters influences the structural integrity and progressive crushing behaviour. In this extensive review each of these parameters is introduced, explained and evaluated. Construction of a well-engineered composite structure and triggering mechanism to strain rate sensitivity and testing conditions followed by failure mechanisms are extensively reviewed. Furthermore, this paper has mainly focused on experimental analysis that has been carried out on different types of FRP composites in the past two decades

An Investigation on Spot-Weld Modeling Complexity for Crash Simulation

In order to design car body structures which are safe during crash, modern automotive manufacturers perform both full-scale experimental crash tests and computer simulation of vehicle crash events using commercially available Finite Element Analysis (FEA) packages such as ABAQUS or LS-DYNA. Use of crash simulations significantly reduces the number of real time crash experiments needed and reduces the time required for design changes. However, in order to capture accurately crash behavior during high-speed impact, a large amount of detailed FEA modeling features such as number and types of elements, mesh element size, number of components, different types of connectors, material properties, and other detailed features are needed. Crash simulation requires explicit time-stepping procedures, which can be computationally expensive for complicated full vehicle models with many components. An important feature in crash simulation is the amount of detail included in modeling spot weld connections. Traditionally for efficiency, simple node-to-node rigid connections for modeling spot weld connections between different components are used, especially when many components are connected in a full vehicle crash model. Recent studies have shown the importance of accurate modeling including elastic stiffness and failure modes for spot welds due to high impact loads in automotive crash analysis. For efficiency and convenience, most commercially available FEA packages now include the option of creating mesh independent spot welds, which allow the user to define the location of the center point of the spot weld and define the spot weld radius on adjacent surfaces of connected components. A distributed coupling to nodes within the radius specified is automatically created which approximates the behavior of a spot weld of finite size. In addition, the size of the rigid spot weld model provides greater accuracy compared to the simple node-to-node connection. However, it has not been until very recent that some researchers and commercially available FEA software have the ability to include important spot weld elastic properties and failure modes combining pull, peal, shear, and torsion. In this work, different levels of complexity in spot weld modeling are examined in terms of sufficient accuracy which can be used efficiently for impact analysis of large connected components and full vehicle crash models. In order of increasing complexity, the following spot weld models are considered and results compared: (a) simple node-to-node rigid connection, (b) rigid mesh independent spot welds, (c) elastic mesh independent spot welds, and (d) elastic with failure mesh independent spot welds. In order to study the fundamental behavior of the different mesh-independent spot weld models, pullout and peal tests between two thin ductile steel plates are performed which isolate different failure modes. Comparisons of reaction force versus displacement curves and internal energy versus displacement for all the different spot weld models are given. Results indicate that the rigid connected results in peak reaction forces which are much larger than elastic spot welds. The spot weld model, which includes failure, follows the same path as the elastic weld but when reaching the particular failure force the reaction remains constant with additional applied displacement. To better understand the behavior of the spot-weld models for crash analysis on a realistic and important automotive component which exhibits complex crushing modes with combined axial and bending a frontal longitudinal rail designed for strength and energy absorption was studied with a node-to-node rigid spot weld compared with mesh independent rigid and elastic spot weld connections. The frontal longitudinal rail is a thin walled closed section located in between the front bumper and the firewall manufactured from two stamped sheets with spot welds on both sides of flanges at discrete intervals along the length. In addition to spot welds, the effect of various shape and size parameter changes including waves, beads, and a small rib for crush initiation that significantly increase energy absorption and crush force efficiency for the rail component are proposed

Design of an Origami Patterned Pre-Folded Thin Walled Tubular Structure for Crashworthiness

Indiana University-Purdue University Indianapolis (IUPUI)Thin walled tubular structures are widely used in the automotive industry because of its weight to energy absorption advantage. A lot of research has been done in different cross sectional shapes and different tapered designs, with design for manufacturability in mind, to achieve high specific energy absorption. In this study a novel type of tubular structure is proposed, in which predesigned origami initiators are introduced into conventional square tubes. The crease pattern is designed to achieve extensional collapse mode which results in decreasing the initial buckling forces and at the same time acts as a fold initiator, helping to achieve a extensional collapse mode. The influence of various design parameters of the origami pattern on the mechanical properties (crushing force and deceleration) are extensively investigated using finite element modelling. Thus, showing a predictable and stable collapse behavior. This pattern can be stamped out of a thin sheet of material. The results showed that a properly designed origami pattern can consistently trigger a extensional collapse mode which can significantly lower the peak values of crushing forces and deceleration without compromising on the mean values. Also, a comparison has been made with the behavior of proposed origami pattern for extensional mode verses origami pattern with diamond fold

Load/displacement and energy absorption performances and improvements of structural members under tensile and compressive loading conditions.

The research programs detailed in this thesis focus on the load/displacement and energy absorption performances and improvements of structural members under tensile and compressive loading conditions. A theoretical model for the prediction of energy absorption capabilities of aluminum foam filled braided stainless steel tubes under tensile loading conditions has been developed based upon the unit cell concept. Comparisons between the energy absorption predictions of the analytical model and experimental observations were found to be in good agreement for assembly lengths of approximately 400 mm. Experimental investigations were also completed for energy absorbers which function under axial compressive loading conditions. The crush characteristics and energy absorption capacity of AA6061-T6 extrusions with centrally located through-hole discontinuities were investigated and analyzed. Three different types of geometrical discontinuities, namely, circular, slotted and elliptical holes were fabricated into AA6061-T6 extrusions which had a length of 200 mm, nominal side width of 38.1 mm and wall thickness of 3.15 mm. (Abstract shortened by UMI.)Dept. of Mechanical, Automotive, and Materials Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2005 .C447. Source: Masters Abstracts International, Volume: 44-03, page: 1485. Thesis (M.A.Sc.)--University of Windsor (Canada), 2005

On the Development of Fold Initiator Patterns to Promote Progressive Folding of Hot Stamped Ultra-High Strength Axial Crush Structures

The effect of fold initiator design on the performance of axial crush rails fabricated using ultra high strength steels (UHSS) is examined in a combined experimental-numerical-analytical study. Of particular interest is the effect of fold initiator pattern and spacing in promoting stable folding. A key factor in introducing UHSS into energy absorbing components is the loss of ductility with increases in strength. Thus, the effect of material fracture limit on the ability of crush structures to fold is also considered. The UHSS steel grade considered for the majority of this research (and all of the experiments) was hot stamped Ductibor® 1000-AS, with a thickness of 1.2 or 1.6 mm and tensile strength of 1000 MPa. In addition, performance metrics, developed as part of this research, are applied to a broader range of steel grades spanning strengths in the range of 270-1500 MPa. Ductibor® 1000-AS double hat sections were hot stamped, spot welded and tested in axial crush under quasi-static and dynamic loading conditions. A baseline fold initiator pattern was first evaluated on axial crush rails that incorporated rudimentary single initiators indented on two opposing faces. Dynamic crush tests considering this baseline pattern repeatedly showed a global buckling mode, parent metal fracture and spot weld failure. The numerical models demonstrated close agreement with the observed buckling and failure modes and the measured force-displacement response. Following these baseline results, a numerical parametric study was undertaken to evaluate the effect of six different fold initiator patterns on the dynamic axial crush response. These patterns consider different design variables such as fold initiator location, sequence, orientation, spacing and symmetry. The progressive folding mode was predicted for three of the six patterns considered. The most stable pattern corresponded to that identified by Wierzbicki and Abramowicz (1983) within their Superfolding Element analysis. This pattern utilizes fold initiators placed on the channel section faces and flanges in an alternating fashion to promote a rolling (serpentine) collapse of the flange. The effect of fold initiator spacing on stability (for the most stable initiator pattern) was further examined for each sheet thickness. The numerical models revealed a strong dependence on initiator spacing and served to identify a specific initiator spacing for each thickness that resulted in stable folding and largely suppressed fracture within the tight folds that form during axial crush; moreover, these initiator spacing values agreed well with those predicted using the analytical model of Wierzbicki and Abramowicz (1983). Experimental assessment of the model predictions was undertaken by performing quasi-static and dynamic axial crush experiments for a subset of the parametric cases comprising the baseline and stable folding initiator patterns and a range of initiator spacing. In general, the crush response of the 1.6 mm specimens agreed extremely well with the model predictions and served to validate the predicted effect of fold initiator pattern and spacing on folding stability and fracture suppression. The 1.2 mm specimens exhibited a global buckling instability that was not predicted by the numerical models. The cause of this instability was attributed to the fold initiator forming process which resulted in significant distortion of the cross-section and a loss of buckling resistance. Subsequent numerical models that combined detailed simulation of the indentation process and mapped the forming predictions onto the crush simulations were able to capture the observed buckling response. As part of the continued analysis of axial crush results, three metrics were developed to predict axial crush performance and potentially serve as design tools for screening material selection and initiator design. One metric, termed the “Relative Bending Limit,” was derived from the ratio of the measured plastic work in V-bend fracture characterization tests to the predicted plastic work in the Superfolding Element analysis. This metric was successfully demonstrated to be a predictor of the fracture extent observed in crush columns made of different materials. Another metric, termed the “Folding Transition Indicator,” was derived from the ratio of the measured slenderness ratio of the crush specimens to the theoretical critical slenderness ratio. The metric strongly reflected the various collapse modes observed in these axial columns. By plotting the two metrics on the same graph, a 2D response map was constructed that successfully captured the overall trends in the fracture extent vs. deformation mode response. This research demonstrates that the analytical design approach in configuring fold initiator patterns has significant potential in promoting progressive folding in hot stamped UHSS. By adopting a carefully designed fold initiator pattern and analytically determined fold initiator spacing, improved folding stability was achieved without significant sacrifice in absorbed energy. The results support the application of Ductibor® 1000-AS in frontal crush structures, but point to the need for considerable care in design of fold initiators for which the current performance metrics should serve as design tools. The current findings are tempered by the fact the axial crush specimens, particularly the thinner 1.2 mm samples, were subject to shape distortion due to the indentation method in producing the fold initiators. In future work, as well as in industrial hot stamping practice, these specimens should be fabricated with fold initiators integrated within the hot stamping dies in order to limit distortion and further improve the axial crush performance of hot stamped Ductibor® 1000-AS components

Effect of multi stitched locations on high speed crushing of composite tubular structures

The present paper experimentally investigates progressive energy absorption of fibre-reinforced polymer (FRP) composite tubular structures under high speed loading conditions. Various multi stitched locations are studied to find a correlation between single and multi-locations of stitches and energy absorption capabilities of composite absorbers. The through-thickness reinforcements are applied into locations of 10 mm, 20 mm, 30 mm, 10–20 m, 10–30 mm, 20–30 mm, 10–20–30 mm and 10–15–20–25–30–35 mm from top of the tubes. It is shown that multi-stitched location can cause several increase of crushing load and consequently increase of energy absorption of composite tube absorbers. The idea would be expanded to other designs which are followed by increase of stitched locations and reduction of the distance between stitches to improve the mean force with a smooth and progressive pattern of crushing load

Optimization of the axial crushing behavior of closed-cell aluminum foam filled welded 1050 al square-cross section crashboxes

Thesis (Master)--Izmir Institute of Technology, Mechanical Engineering, Izmir, 2009Includes bibliographical references (leaves: 194-209)Text in English; abstract: Turkish and Englishxx, 211 leavesThe crushing behavior of partially Al closed-cell foam (Alulight AlSi10) filled 1050H14 Al crash boxes was investigated at quasi-static and dynamic deformation velocities. The quasi-static crushing of empty and filled boxes was further simulated using LS-DYNA. Finally, the crushing of partially foam filled 1050H14 crash boxes was optimized using the response surface methodology. The used optimization methodology was also applied to the boxes made of a stronger Al alloy, 6061T4 Al, and filled with a higher strength Al foam, Hydro Al closed cell foam, in order to clarify the effect of box material and foam filler strength on the crushing behavior of the filled boxes. Within the investigated tube thickness and foam relative density range, the energy absorption of 1050H14 boxes was optimized at 3 mm wall thickness and 0.1114 (Alulight) and 0.0508 (Hydro foam) foam filler relative density. The increase in specific energy absorption of 1050H14 crash box was 5.6% with Alulight and 21.9% for Hydro foam filling. The SEA values of empty, partially and fully foam filled boxes were predicted as function of box wall thickness between 1 and 3 mm and foam filler relative density between 0 and 0.2, using the analytical equations developed for the mean crushing loads. The analysis indicated that both fully and partially foam filled boxes were energetically more efficient than empty boxes above a critical foam filler relative density. Partial foam filling however decreased the critical foam filler density at increasing box wall thicknesses

Model updating of crash box structures for crashworthiness study

The crash box structure is an essential structure of the front side members of a car body structure. It absorbs the kinetic energy during the event of a collision by plastically deform to absorb the impact energy efficiently. Various designs are applied towards the structure with different materials, configurations, and imperfections or trigger mechanisms. Crash box with trigger mechanisms is often a subject in crashworthiness studies, however, this research will have an approach to dealing with the structure with modal testing through experimental and computational analysis due to the location of the structure that exposed to vehicle vibration as well. As discrepancies occur, the model updating technique is utilised to identify and update the sensitive parameters that cause the discrepancies. The parameters are then used in the crashworthiness analyses to determine their effect towards the crashworthiness output of the crash box structure. The crash box structures are modelled in finite elements before being analysed with the normal mode analysis in MSC Patran and MSC Nastran and quasi-static analysis in Abaqus. Five different fabricated structures are made up of two parts attached using a spot weld with different designs of trigger mechanisms. Three approaches to joining elements are used for the finite element model: CWELD, CBEAM, and CBAR. The modal behaviour for all modelling is identified by using SOL 103, while the experimental modal analyses are conducted with the use of an impact hammer test with the roving hammer method to obtain the modal responses. The model updating method was conducted to reduce the discrepancies between the experimental and the computational data. Sensitivity analyses are executed to find the most sensitive model updating parameters. The results obtained by this study demonstrate that the use of CBAR joining element is the best to replicate the spot weld joining, where for all five types of crash box structures, the CBAR elements did show a significant percentage of error compared to CWELD and CBEAM for all types of crash box structures, while the most sensitive parameters that affect the modal behaviour of the structures are Young’s modulus of AA-6061, followed by the density of AA-6061 and Young’s modulus of spot welded joint. In terms of crashworthiness analyses, it is identified that the use of updated parameters in crashworthiness analyses compared to the initial results of crashworthiness output did show a small change where the crashworthiness output of the structure is slightly higher for both primary and secondary peaks as well as for the magnitude of the absorbed energy. The outcome of this research will contribute towards the field of mechanical vibration and crashworthiness, especially in the automotive industry, in which this research focuses on the optimization method of the modelling to improve the accuracy and reliability of the computational prediction

Crashworthiness Characterisation of the Car Front Bumper System Based on FEA Analysis

This thesis investigated different designs and material selections of vehicle front bumper system to improve the vehicle crashworthiness during the low impact speed (impact velocity=15km/h, 9.32mph) via FEA simulations. The primary purpose is to identify the most important parameters directly related to the improvement of crashworthiness using numerical parametric study. It is found the cross-section profile, curvature shape, material of the bumper beam, together with the connection to the crash box have been all identified that directly influence the crashworthiness performance of the front bumper system. The bumper system, including the sub-components such as bumper beam, crash box, and the connection methods were carried all the parameters, including a number of folds, curvature shapes and spot welds were in-built while creating them into the CAD models using Solidworks. The final assembled complete bumper system is then imported into the ANSYS for further geometry checks and adjustment. Solver Autodyn is used to perform the FEA simulation, and numbers of results files were generated. Results files such as force reaction, plastic work, and equivalent stress, normal stress was all exported it into the Excel for parametric analysis and discussions. Cross-section Profile-Out of proposed Single fold (fold 1) and Triple fold(fold 3) bumper beam profiles, Double fold (fold 2) bumper beam profile presented the best results of force reaction on both smoothness and force value, while the plastic work remained almost identical to profile fold 1 and 3 gained. Fold 2 profile is considered as a good performer since this profile regulated the deformation behaviour of the beam resulted in a smooth increasing force reaction curve. Where the force reaction curve on both fold 1 and fold 3 were fluctuated dramatically due to catastrophic structural failure. Material-In between structural steel and aluminium alloy used in the bumper beam, while the structural steel made bumper beam achieved good force reaction and plastic work. Switched to aluminium can achieve similar force reaction trend and rate with Cross-section neglectable amount of plastic work reduced. Particularly the weight of the bumper beam is dropped down to 5.357 kg while maintaining similar crashworthiness performance to the structural steel. Crash box Crash box connection- The bonded connection is considered as an ideal scenario and was xvii Sensitivity: Internal favoured in much other literature due to it simplifies the connection setting in the FEA environment since it automatically considers it as perfect contact. Three alternative connection methods were therefore proposed to simulate the more realistic scenario. It defined as welding connection that is constituted by a number of spot welds at left, right, top and bottom of the crash box. Since the bonded method contains no spot welds, a method of weld L+R was indicated by totally 4 spot welds appeared at both left and right side of the crash box. On top of this, 4 additional spot welds were added to the top and bottom of the crash box. Totally 4 spot welds were added only to both the top and bottom of the crash box to extend the comparison. While both bonded and weld L+R methods suffered from buckling effect to the crash box, particularly concentrated at the left and right side with high equivalent and normal stresses. It is discovered weld full method provided promising results by reducing the buckling effect to both left and right faces of the crash box, and also managed to lower the equivalent stress down to 336.48MPa and normal stress on the connection surface down to 66MPa. Weld T+B also observed similar performance when compared with both bonded and weld L+R methods. While registered with very small amount of equivalent and normal stresses, the buckling effect is significantly reduced. This thesis contributed the knowledge to the improvement of vehicle front bumper system. Particularly to the failure mode of both bumper beam and crash box, and offered the related optimisation.N/