Quasi-static Axial Compression Research Articles

On crashing behaviors of aluminium/CFRP tubes subjected to axial and oblique loading: An experimental study

Abstract Thin-walled energy-absorbing structures rarely experience in pure axial loading in real crash events, but rather a combination of axial and off-axial loads. In this perspective, it is critical to understand the oblique crushing process of thin-walled structures. To address this issue, circular aluminum and carbon fiber reinforced plastics (CFRP) tubes were experimentally investigated for characterizing their crashworthiness subject to quasi-static axial and oblique compression in this study. The tests were conducted at five different loading angles (θ) of 0°, 5°, 10°, 20° and 30° to the tubal axis. Five sets of specific fixtures were fabricated to apply the desired axial and off-axial loads onto the aluminum and CFRP specimens, respectively. The failure modes, load-displacement curves, crushing force and energy absorption of all the specimens were analyzed; and the effects of loading angle were explored. It is found from the experiments that with the increase in loading angle, aluminum tubes were more prone to collapse in an irregular diamond mode (Id) instead of axisymmetric concertina mode (Ac), while the CFRP tubes collapsed in much more complex failure modes which included splaying mode (Sp), tearing mode (Te), socking mode (So), micro-fragmentation mode (Mf) and catastrophic failure (Cf). As for the energy absorption characteristics, the loading angle (θ) ranged from 0° to 10° had little impact on the energy absorption for the both aluminum and CFRP tubes, nevertheless, the energy absorption of the CFRP tubes decreased more significant from θ = 10° to 30°, while that of aluminum tubes declined fairly steadily.

Crashworthiness of different composite tubes by experiments and simulations

Abstract Composite tubes show a good energy absorbing ability and they have great potential as energy absorbing components to replace traditional metal structures in automobiles, aircrafts and other transportation. This paper aims to investigate the impacts of geometrical parameters, including intermediate diameter, wall thickness and upper end diameter, on the specific energy absorption (SEA) of composite tubes, metal tubes, foam-filled tubes and hybrid tubes. The mechanical characteristics (axial compression response) of these tubes were numerically predicted by commercial finite element (FE) package LS-DYNA. Quasi-static axial compression tests were performed to determine failure parameters of glass fiber reinforced polymer (GFRP) used in this paper. Stress-strain curves of polyurethane foam and aluminum foam were also obtained by tests. Finite element models of hollow GFRP, aluminum and aluminum-FRP tubes and polyurethane foam-filled and aluminum foam-filled composite tubes were established respectively. Configurations of these numerical models include circular, square and tapered (5 different upper end diameters) tubes. In optimization part, structural parameters optimization was carried out by response surface method (RSM). Results review that in general, SEA of circular tubes increases with smaller diameter-thickness ratio. In comparison part, SEA of circular, square and tapered tubes were compared. Results show that changing upper end diameter of tubes has great impacts on their energy absorption capacity, but sensitivities of SEA to geometrical parameters and cross-section shapes differ depending on materials of tubes and foam filling.

Comparative analysis of crashworthiness of empty and foam-filled thin-walled tubes

Quasi-static axial compression tests were conducted on two types of empty aluminum alloy tubes (circular and square) and five types of aluminum ex-situ foam filled tube structures (foam-filled single circular and square tubes, foam-filled double circular and square tubes, and corner-foam-filled square tube). The load-deformation characteristics, deformation mode and energy absorption ability of these structures were investigated. Several parameters related to their crashworthiness were compared, including the specific energy absorption, the energy-absorbing effectiveness factor, etc. The influence of physical dimension on the crashworthiness of these structures was explored. Dimensions of the inner tube were found to have significant influence on the structural crashworthiness of foam-filled double tubes. The averaged crush force, specific energy absorption, energy absorption per stroke and energy-absorbing effectiveness factor of thin-walled circular structures are higher than those of thin-walled square structures, respectively. Foam-filled single and double circular tube structures are recommended as crashworthy structures due to their high crush force efficiency and energy-absorbing efficiency.

A novel method for enhancing the energy absorption characteristics of circular tubular structures under axial splitting

The present research is an attempt to introduce a novel method for axial splitting of brazen tubes in order to eliminate the dependency of the conventional splitting mechanism on a hardened steel die and improve the energy absorption capability of the presented method. Some circular tubular samples were cut out from commercial brazen tubes and the specimens were then filled with natural rubbers with different shore hardness. For this purpose, the tubes were filled by raw rubbers and placed in an autoclave for a specific time at a controlled temperature to complete the curing process of rubbers. Some slits were created on one side of the rubber-filled tubes and the specimens were compressed during quasi-static axial compression loading between two rigid plates. Based on the experimental results, the effects of diameter and wall-thickness of the tubes, length and number of initial slits, rubber shore hardness and length of initial extra rubber on the energy absorption characteristics of the specimens are investigated. Also, experimental results of the presented splitting method are compared with those of the conventional splitting method (using conical dies for splitting of empty tubes) to find an optimized energy absorber. It was found that in comparison with the conventional splitting method, the presented technique eliminates the restrictions of using almost heavy dies which significantly decrease the overall mass of the system and moreover increases total energy absorption and keeps crush force efficiency in the range of classical splitting.

A Proximally-Adjustable Variable Length Intramedullary Nail: Ex Vivo Quasi-Static and Cyclic Loading Evaluation

An adjustable-length intramedullary (IM) nail may reduce both complications secondary to fracture fixation and manufacturing costs. We hypothesized that our novel nail would have suitable mechanical performance. To test this hypothesis, we manufactured three prototypes and evaluated them in quasi-static axial compression and torsion and quasi-static four-point bending. Prototypes were dynamically evaluated in both cyclic axial loading and four-point bending and torsion-to-failure. The prototypes exceeded expectations; they were comparable in both quasi-static axial stiffness (1.41 ± 0.37 N/m in cervine tibiae and 2.30 ± 0.63 in cadaver tibiae) and torsional stiffness (1.05 ± 0.26 N·m/deg in cervine tibiae) to currently used nails. The quasi-static four-point bending stiffness was 80.11 ± 09.360, greater than reported for currently used nails. A length-variance analysis indicates that moderate changes in length do not unacceptably alter bone-implant axial stiffness. After 103,000 cycles of axial loading, the prototype failed at the locking screws, comparable to locking screw failures seen clinically. The prototypes survived 1,000,000 cycles of four-point bend cyclic loading, as indicated by a consistent phase angle throughout cyclic loading. The torsion-to-failure test suggests that the prototype has adequate resistance to applied torques that might occur during the healing process. Together, these results suggest that our novel IM nail performs sufficiently well to merit further development. If brought to market, this adjustable-length IM nail could reduce both patient complications and healthcare costs.

Crashworthy characteristics of axial quasi-statically compressed Bombyx mori composite cylindrical tubes: Experimental

The study investigated the energy absorption response and load carrying capability of Bombyx mori (B. mori) natural silk fibre/epoxy composite cylindrical tubes subjected to an axial quasi-static crushing test. The reinforced cylindrical composite tubes were prepared using hand lay-up technique. Varied numbers of B. mori layers, 12, 24 and 30 were used to fabricate the tubes; their corresponding diameters were 33.3, 62.3 and 80.6 respectively. The crashworthiness of the cylindrical tube was analyzed by measuring the specific energy absorption, peak load and total energy absorption as a function of tube diameter/number of layers under a quasi-static axial compression load. Failure mechanisms of the tubes were analyzed using scan electron microscopy (SEM) and high resolution photographs obtained during test. Generally, the result showed increase in crashworthiness behaviour as the numbers of B. mori layers increased. The 12 layer tube (33.3 mm diameter) showed a progressive crushing failure starting from the upper half; the 24 layer tube (62.3 mm diameter) depict a mid-length crack failure, while the 30 layer tube (80.6 mm diameter) showed a progressive crushing failure from the lower side of the tube. The SEM micrographs of suggest that failure mechanism includes: matrix crack, fiber delamination, fiber pull out, tear and fibre breakage.

Quasi-Static Axial Compression of Origami Crash Boxes

The origami crash box has been recognized as an efficient energy absorption device. In this paper, quasi-static axial compression tests and numerical simulations are carried out to investigate the energy absorption capacity of origami crash box. The complete diamond mode could be successfully triggered, which indicates that this collapse mode is insensitive to geometric imperfection when the tube is subjected to quasi-static loading. And the results confirm that axially compressed tubes with longer modules ([Formula: see text]) renders higher mean crushing force than those with short modules ([Formula: see text]). Moreover, in order to figure out the energy dissipation percentage of each region in origami crash box, the plastic deformation of shells in two representative regions is measured and analyzed by utilizing electrical measurement and noncontact optical measurement. The results reveal that about 10% of total energy is absorbed by those shells, which is large enough to affect the prediction accuracy of expressions deduced by super folding element theory.

Compression performance of column-cell sandwich composite

Abstract A new sandwich structure which core is made of thin-walled semi-ellipsoidal shell is designed, column-cell sandwich composite was prepared by pre-panel preparation process. A series of quasi-static axial compression experiments were carried out on 2 × 2 thin-walled semi-ellipsoidal shell, the compression deformation and yield behavior of thin wall semi-ellipsoidal shells with different materials, diameters and wall thicknesses were studied by means of ANSYS/LS-DYNA finite element simulation and experiment. Then, the effect of filling mode of epoxy resin on the mechanical properties of Column-cell sandwich composites was studied. The results show that the deformation process of the thin spherical shell can be divided into local flattening, axisymmetric depression, non-axisymmetric depression and compaction stage. As the wall thickness increases, the deformation mode changes from the polygon to the ring and the deformation process become three stages; small diameter requires larger force under the conditions of the same compression displacement, as the diameter increases, the critical displacement of flipping and asymmetric buckling increases; Epoxy filled in the spherical shell of the sample specific compression performance is better than filled in the outer shell and better than unfilled with epoxy resin.

Influence of braided fabric on the fracture modes of a composite tube under quasi-static compression

The deformation behavior of single-layer braided fabric and its influence on the fracture modes of composite tubes under quasi-static axial compression were studied. By changing the parameters of the manufacturing process, braided fabrics with varying structures were produced and were further cured into braided composite tubes. Quasi-static compression experiments were conducted on the tubes, and the crush process was recorded on camera to analyze the deformation of the braided fabric. By employing the finite element method, a numerical model of a composite tube at the yarn scale was established to further verify the role of braided fabric in the process. Two fracture modes that depended on the fabric structure were also observed. The tension in the braiding yarns in the bucking section tends to cause them to separate. Braiding structures with larger braiding angles and more interlacing points between yarns provided more resistance to prevent yarns separating from the braided structure and led to a folding fracture mode. In contrast, a splaying fracture mode occurred in braided fabrics with smaller angles.

Multi-response optimization of crashworthiness parameters of bi-tubular structures

This article aims at presenting multi objective optimization of parameters that affect crashworthiness characteristics of bi-tubular structures using Taguchi method with grey relational analysis. To design the experiments, the <i>L</i>₉ orthogonal array has been used and based on that, the inner tubes have been fabricated by varying the three influence factors such as reference diameter, length difference and numbers of sides of the polygon with three levels, but all the outer cylinders have the same diameter and length 90 mm and 135 mm respectively. Then, the tailor made bi-tubular steel structures were subjected into quasi static axial compression. From the test results it is found that the crushing behaviors of bi-tubular structures with different combinations were fairly significant. The important responses (crashworthiness indicators) specific energy absorption and crush force efficiency have been evaluated from load - displacement curve. Finally optimal levels of parameters were identified using grey relational analysis, and significance of parameters was determined by analysis of variance. The optimum crashworthiness parameters are reference diameter 80 mm, length difference 0 mm and number of sides of polygon is 3, i.e., triangle within the selected nine bi-tube combinations.

Crashworthiness analysis of double section bi-tubular thin-walled structures

This article aims to present the crashworthiness performance of double section bi-tubular thin-walled structures. Double section bi-tubes were made from stainless steel sheet and consist of an outer circular cylinder and an inner tube with any one of polygonal section such as triangle, square or hexagon. By keeping the outer cylinder dimensions constant, the effect of changes in the inscribed diameter of polygonal section and the various polygonal section of the inner tube on quasi-static axial compression is studied. Bi-tubular structures with hexagonal inner tube have more energy absorption capability than the other bi-tube combinations and the single cylinder.

Influences of Thickness and Geometrical Change from Draw Forming in Quasi-Static Axial Compression Simulation

In the current industrial practices in the automotive field, the forming effects are neglected in the automotive crash analysis simulation. However, in reality, the forming process alters the structural behaviour of these components significantly. The objective of this paper is to present the effect of draw forming in the quasi-static axial compression analysis. In the present work, a circular cup is draw formed using Dual Phase (DP600) steel followed by a compression analysis to quantify the effects of non-uniform thickness distribution and the geometrical change on the cup. Numerical compression simulation was carried out with RADIOSS to identify these effects which were modelled using, in case A, a CAD circular cup and, in case B, a formed circular cup from draw forming. The experimental work was done to validate the forming model before compression analysis. Quasi-static axial compression simulation results revealed that the peak load and the energy absorbed for case B are lower by 26.91% and 17.84% respectively compared to case A. The compression analysis results demonstrate that the effect of non-uniform thickness distribution from draw forming process gives significant effect in the subsequent analysis. Therefore, the forming effects should be considered when conducting a crash simulation to increase the crash prediction and safety.

Collapse behavior of thin-walled conical tube clamped at both ends subjected to axial and oblique loads

The structures of the vehicles during the crushing processes or accidents not only experience direct or axial collisions but sometime these structures are crushed off-axially. Therefore, it is very crucial to study whether or not a foam-filled tube is capable of supporting the oblique compression forces efficiently and effectively. In this paper, investigation of the axial and oblique loading collapse behavior of thin-walled conical tube clamped at both ends is presented. Several numerical simulations using ABAQUS finite element explicit code are carried out to study crashworthiness characteristics of empty and foam-filled thin-walled conical tubes clamped at both ends. In order to verify these numerical results, a series of quasi-static axial and oblique compression tests are performed. The validated finite element model was then used for the parametric studies, in order to determine the effect of the empty and filler tube geometry parameters (i.e. semi-apical angle) and loading parameters (i.e. load angle) on the energy absorption and mean crushing load. The primary outcome of this study is to provide information for the use of foam-filled conical tubes as energy absorbers where oblique loading is expected.

Quasi-static axial crushing experiment study of foam-filled CFRP and aluminum alloy thin-walled structures

Thin-walled aluminum alloy (Al alloy) structure, carbon fiber reinforced plastics (CFRP) tube, aluminum foam (Al foam) and polyurethane foam (PU foam) all can be used as good energy absorbers in automobile, aviation and other industries for their light weight and high energy absorption capacity. In order to clarify the advantages of the design modes, this article studies the crushing behaviors of circular, hexagonal and square CFRP and Al alloy tapered tube and their foam-filled structures subjected to quasi-static axial compression, analyzes and compares the collapse modes and force–displacement curves of these investigated structures as well as calculates the energy absorption (EA) and the specific energy absorption (SEA) of these investigated structures. Experimental results show that the CFRP tapered tubes have higher SEA than that of the Al-alloy tapered tubes and the circular CFRP tubes filled with PU foam have better energy absorption capacity than that of the square and hexagonal structures. In addition, the SEA of the CFRP tube filled with PU foam is 30% higher than that of the Al alloy tube filled with Al foam. Therefore this article leads to a conclusion that PU foam-filled CFRP tapered tube is a potential structure for energy absorber and light weight design.

Frusta structure designing to improve quasi-static axial crushing performances of triangular tubes

To improve quasi-static axial crushing performances of thin-wallled triangular tubes, frusta structures were designed and fabricated. Quasi-static axial compression experiments were carried out to reveal the collapse mode and energy absorption characteristic of the triangular frusta tube. Peak loads and mean crushing forces (MCFs) of tubes with different taper angles were compared. In-extensible and extensible collapse modes were suggested to predict the MCF of the triangular frusta tube with small and great taper angles, respectively. A new collapse mode, inward folding, was observed in the experiments. An energy absorption stability factor was defined to evaluate the anti-crushing efficiency of the triangular frusta tube. With greater taper angles, the energy absorption stability factor is much closer to 1, denoting more stable deformation style. It is concluded that frusta structures with taper angles effectively enhance the anti-crushing efficiency and stability of thin-walled triangular tubes.

Design and experimental verification of composite impact attenuator for racing vehicles

Implementing measures to enhance collision energy absorption of a racing vehicle is essential to protect the vehicle and its driver and maximize the driving performance. In this study, based on the energy absorption characteristics of composites, the requirements of competition rules, and the overall vehicle arrangement, a preliminary design of an impact attenuator is performed. This paper will design the basic model with rules requirement in second section, and refer existing composite material-corrugated beam energy absolved structure, and write in half-corrugated beam energy absolved structure, so the model structure can be parameterize. Based on commercial nonlinear finite element analysis software LS-DYNA, established the numerical model. Subsequently, the optimization is divided into structural and lay-up optimizations. Using the LS-OPT software, and based on the response surface analysis method, the structure is optimized to obtain a composite impact attenuator model with the highest possible specific energy absorption. The lay-up of the model is optimized to attain a final lay-up with the minimum weight. Quasi-static axial compression and dynamic drop-weight impact tests are conducted to verify the optimization design. Finally, the composite impact attenuator of the racing car with high energy absorption efficiency, high specific energy absorption, and light weight is achieved.

Quasi-static Axial Crushing Behavior of Thin-walled Circular Aluminum Tubes with Functionally Graded Thickness

In this paper, the crushing behavior of circular aluminum thin-walled tubes with functionally graded thickness (FGT) are investigated experimentally. To this aim, three different thickness grading patterns are introduced to the longitudinal direction of tubes using a grading function, and then specimens are tested by universal testing machine under quasi-static axial compression loading. In addition, to show the efficiency of FGT tubes, the quasi-static axial crushing performance of FGT tubes are compared with their uniform thickness (UT) counterparts at the same weight. The test specimens have been made of commercial quality 6060 aluminum alloy and manufactured with computerized numerical controlled (CNC) machining workbench. Initial crush force (ICF), total energy absorption (EA), specific energy absorption (SEA) and mean crush force (MCF) values are measured from the tests to infer the quasi-static axial crushing performance of the tubes. The test results showed that the energy absorption characteristics of FGT tubes are better than the UT counterparts and FGT tubes allow effective control of the energy absorption parameters when compared with the UT tubes due to their varying stiffness along their longitudinal direction.

Formation of a square tube having a middle circular section for axial crushing

A new forming method for the tapered square tube is demanded. In this study, a four-stage forming process for a square tube having a circular section in the middle from a seamless round pipe is developed. The transitions between the square and the circular sections form the tapered walls for the reduction in initial peak load. The height of the circular section is minimised to increase the number of folds per unit length of the tube. In the first and the second stages, about half length the pipe is expanded into a circular section before compressing it into a square section. The square section is formed by pushing the expanded circular section through a square die with a square punch. This process is repeated at the opposite site of the pipe in the third and fourth stages to form the square tube. Both finite element simulation and experiment are performed to evaluate this process. A square tube having a circular middle section is successfully obtained from both the simulation and experiment. The corner radii of the square section reduce when the diameters of the circular dies in the first and third stages are increased. However, the wall thickness distribution of the square section becomes small and uneven. The height of the circular middle is reduced to around 10 mm by increasing the punch strokes in the first and third stages. A quasi-static axial compression test is performed on the square tube. The compressive load has an initial peak value of 250 kN. The crush force efficiency of the square tube, i.e. the ratio of its average load to the initial peak load is about 54%, much higher than the one for the plain straight tube which is usually around 30%.

Crash analysis of composite energy-absorbing cylindrical impact attenuator

Thin-walled composite structures are becoming increasingly popular over metals for crashworthy applications in the automotive industry due in part from advantages such as their higher strength to weight ratio. In this study, the analysis of the crash behavior was conducted by means of a series of quasi-static axial compression tests and LS-DYNA simulations. A set of comparative quasi-static compression tests were conducted on simple composite tubes with different lay-up orientations. Based on experimental data on load/displacement and on the comparison between results of experiments and simulations, the factors affecting energy-absorbing capacity were discussed and the mechanism of failure in composites during the crushing process was concluded. Load versus displacement diagrams confirm that the composite cylindrical attenuator shows high energy-absorbing characteristics and efficiencies. The energy-absorbing capacity is strongly affected by the ply wrap angle. Specific energy absorption increases with the increasing of angle of the fiber. Based on the analysis of these experiments and simulations, factors influencing the value of specific energy absorption are determined and design principles of composite impact attenuators are provided.

Effect of initiator, design, and material on crashworthiness performance of thin-walled cylindrical tubes: A primary multi-criteria analysis in lightweight design

Two major requirements for crush analysis of thin-walled cylindrical tubes are being lightweight and having good crashworthiness. Thin-walled cylindrical tubes, which are either empty or foam filled, can potentially be used in all vehicles and moving parts such as road vehicles, train, aircrafts, ships, lifts and machinery to protect passengers and the structure itself during impact. This paper discusses an idea of utilizing the initiator on the foam-filled thin-walled circular tubes with stiffened annular rings to increase the specific energy absorption (SEA) and prevent the sudden force applied to the main part of the automotive and its occupants. Effect of initiator, at the top of the foam-filled aluminum tube, different densities of rigid polyurethane foam, and number of annular rings under axial compression were described through energy absorption, crush force efficiency (CFE), and mass of structure. In order to verify the numerical results, a series of quasi-static axial compression tests was performed, and both load–displacement curves and deformation mechanism of the structure were analyzed. The results of multi-criteria decision analysis (MCDA), by incorporating numerical and experimental data, showed that in the considered material and geometry, the design with an initiator, four rings tube, and higher density of foam have superior performance in terms of energy absorption, CFE, and mass. More debate on effect of initiator would help to reach the simultaneous improved crashworthiness structure and lightweight design with greater degree of accuracy in the hope of reducing the occupant injury in a collision.