Dynamic Crush Tests Research Articles

Experimental and Numerical Investigation of Energy Absorption Characteristics of a E-Glass/Epoxy Crash Box

Crash boxes are energy absorbing components generally placed at the front end of cars to reduce the amount of damage at especially low impact velocities. The number of electric vehicles has been increasing recently, so weight reduction studies are. For this reason, lighter glass or carbon fiber reinforced composite crash boxes are preferred instead of steel ones. In the current study, the dynamic compression behavior of a rectangular cross-section thin-walled composite crash box was investigated both experimentally and numerically. The main aim of the study was to understand the effective damage modes and monitor the deformation sequence experimentally and numerically. Once the numerical model is verified then it can be further used to reveal the behavior at different impact velocities and geometries. The methodology followed in the study first started with the static mechanical characterization of the composite material. Within the scope of this study, 2×2 twill-woven glass fiber/epoxy crash boxes were produced using the vacuum bagging method. Quasi-static compression and tension tests were carried out in accordance with ASTM D3039 and ASTM D6641 standards. In the numerical part, Radioss finite element package was used with the material model of MAT 25 along with the failure option of Tsai-Wu. Experimental dynamic crushing tests of the crash box was carried out using a custom made drop-weight tester at impact velocity of 4.4 m/s and dropping mass with 450 kg. The material model constants were obtained once the coupon based static and dynamic tests were completed. From the dynamic crushing tests, maximum and mean force values of 225 and 65.0 kN were noted, respectively. There is close agreement between the experimental and numerical results both in terms of force and displacement values. This verified numerical model can further be used to investigate the crushing characteristics at different impact conditions.

Dynamic axial crushing behaviors of circular composite tubes with different reinforcing fibers and triggers

The choice for a proper external trigger and fiber hybridization configuration has a significant impact on the stability of the crushing process and material cost for composite structures in crashworthiness. However, there is still a lack of a thorough understanding of impact characteristics and energy-absorption mechanisms. This study explores the axial crushing responses and crashworthiness characteristics of energy-absorption composite structures by both experiment and finite element analysis. A series of dynamic crushing tests were conducted for three types of composite tubes under the same crushing velocity of 1.944 m/s, including carbon fiber reinforced polymers (CFRP), glass fiber reinforced polymers (GFRP), and CFRP/GFRP inter-layer hybridized composites. The configuration of the composite tubes includes: (i) CFRP composite tubes with a single 45° chamfer trigger (T1), a combined 45 °chamfer and outward-folding crush-cap (T2), and a combined 45 °chamfer and outward-folding crush-cap with a cavity (T3); (ii) GFRP and CFRP/GFRP hybrid composite tube with T2 trigger. A stacked-shell model was developed to investigate the energy-absorption mechanisms. Three distinct failure modes have been found for composite tubes with T1, T2, and T3 triggers, separately, named splaying, outward-folding, and outward-folding with local buckling. The CFRP composite tubes with the T1 trigger exhibited the best crashworthiness performance, while the T2 trigger reduced the friction interaction between the splaying fronds and the platen, causing a 67% reduction of specific energy absorption (SEA)/mean crushing force (MCF). In the meantime, the T3 trigger boosted 101.9% of SEA/MCF from T2. With the same T2 trigger, the GFRP composite tube showed a better crashworthiness performance than the CFRP composite tube: 35.5% reduction of initial peak crushing force (IPCF), 68.6% and 98.5% increment of MCF and SEA respectively. It has been found that the outermost layers dominated the energy absorption behavior, which matches well with the observation that replacing the central CFRP plies with GFRP ones results in similar crashworthiness characteristics between CFRP and CFRP/GFRP hybrid composite tubes. The findings in this study contribute to providing practical guidelines for the crashworthiness design of heavy duty composite structures, such as railway vehicles.

Experimental and numerical study on static and dynamic axial crushing of square aluminum tubes: Effects of cutouts

The collapse of tubes under axial load is an important subject from the safety point of view, particularly in the design of energy absorbing devices used in many engineering applications. In this study, quasi-static and dynamic experiments were carried out on square thin-walled aluminum extrusions to investigate the effects of circular holes. Cutouts were introduced in the four corners of the square-section tube, not far from the end boundary of the tube, in order both to decrease the first peak load on the load-displacement characteristic and to control the collapse mode. Different aspects, such as the buckling modes and the energy absorption in quasi-static axial crushing tests, as well as dynamic effects and material rheology contributions in dynamic crushing tests, have been examined. For the dynamic tests, the parameters were the impacting mass and its velocity. The results showed a drop in the first peak function of the openings’ radius and the tube’s energy absorption capacity was kept. A comparison between static and dynamic tests results was carried out and the interpretation of the results in terms of deformation mechanism and energy absorption was discussed. Numerical simulations with the finite element code ABAQUS were conducted to confirm the experimental findings. The results of different numerical models, implicit and explicit calculations, that contribute to a basic understanding of the buckling and prediction of the crash behavior of the aluminum components without and with the cutouts are presented.

Design and Numerical Simulation of Pyramidal Prefolded Patterned Thin‐Walled Tubes

An improved pyramidal prefolded pattern was designed and applied to thin‐walled tubes. This delicately designed pattern modularizes the tube to control the folding process and act as an inducer to trigger deformation modes with outstanding crushing performance. Dynamic crushing tests were conducted numerically; the simulation results reveal that the patterned square tube developed a deformation mode with shorter wavelength, better load consistencies, and higher energy‐absorption efficiency (up to 29%) than that of the traditional counterpart. Moreover, geometric analysis was performed and structural improvements were conducted by applying the optimal geometric parameters onto an octagonal profile. The designed patterned octagonal tube collapsed into a highly efficient deformation mode known as diamond mode. Furthermore, the comparative results show that patterned octagonal tubes demonstrated an energy absorption up to 90.1% higher than that of a conventional square column while improving the geometric compliance. These findings enrich research on patterned tubes and provide new explorations for the development of high‐performance energy‐absorbing structures.

Experimental results of medium velocity impact tests for reinforced foam core braided composite structures

Absorbing impact energy at subsystem level is an attractive idea that is emphasized by new composite reinforcement techniques such as stitching or pinning. This paper reports experimental results of medium velocity impact tests carried out on several arrangements of reinforced foam/braided composite structures. The tests consisted of a steel ball shot at a velocity of 110 m/s from a gas gun impacting the structures on their leading edge. Post-mortem tomography analysis delivered very rich information which shed light on the damage mechanisms that the composite structures underwent. In addition, two fast-speed cameras were used to derive the energy absorption during the impact. Absorption capabilities were also compared with those of dynamic crushing tests (reported in a companion paper) and some designs clearly exhibited promising behavior as shock absorbers.

Experimental study of impact energy absorption by reinforced braided composite structures: Dynamic crushing tests

High speed dynamic loadings such as small engine fragments, bird strike, tyre impact or ice debris are a concern for many aeronautical structures, as they can create severe damages raising safety issues. A strategy to develop dedicated mechanisms for energy absorption of high speed dynamic impact debris at sub-component level is therefore proposed by means of several reinforced foam-woven composite structures. Among the tests for evaluating the mechanical performances, dynamic crushing tests were performed on a slice of such reinforced composite structures to evaluate their energy absorption. Using simultaneously load signal and fast camera imaging, the tests were analyzed to provide important informations such as damage mechanisms and displacement-load-energy absorption values. At the end, quantitative criterions are presented in order to distinguish the designs that have a good potential for absorbing shock energy and for getting a better understanding for designing reinforced composite structures.

Controlling the Energy Absorption Capability of a Unidirectional Carbon Fiber Reinforced Plastic Tube Using a Double-Sided Plug

Quasi-static and dynamic crush tests of a unidirectional carbon fiber reinforced plastic (CFRP) circular tube were performed, and its energy absorption capability was controlled using a double-sided plug. It was revealed in the quasi-static crush test that its energy absorption capability was controlled significantly from 8 to 178 kJ/kg by changing the curvature of the plug. The range of energy absorption covers almost all types of CFRP tube reported in the literature. A dynamic crush test up to 55 km/h was then performed by drop weight impact tests. The energy absorption capability of the CFRP tube in the dynamic crush test was very similar to that in the quasi-static crush test. A simple design concept of energy absorption for a CFRP tube, using the double-sided plug, was proposed.

Dynamic crushing behaviour of agglomerated cork

For reasons of energy saving and pollution reduction, there is a growing interest in the development of lightweight structures manufactured with materials of natural origin and recyclable. Agglomerated cork is a mixture of natural cork and an organic binder, and can be considered an alternative to polymeric foams used in structural applications with a high capacity of energy absorption. One of these applications involves impact-absorbing elements in vehicles, which are subjected mainly to dynamic compressive loads. In this work, the dynamic crushing behaviour of agglomerated cork was experimentally studied, analysing the influence of the specimen thickness on the energy-absorption capacity, contact force, displacement, and strain. Dynamic crushing tests with specimens of four different thicknesses were performed in a drop-weight tower. An increase in the maximum contact force, displacement, and strain was observed when the impact-energy/thickness ratio increased. For each specimen thickness a linear variation of the maximum displacement and energy absorbed with the impact-energy/thickness ratio was found. It was observed that the energy absorbed by agglomerated cork did not depend on the specimen thickness, but only on the impact energy.

Simulating the Response of a Composite Honeycomb Energy Absorber. I: Dynamic Crushing of Components and Multiterrain Impacts

AbstractThis paper describes the experimental and analytical evaluation of an externally deployable composite honeycomb structure that is designed to attenuate impact energy during helicopter crashes. The concept, designated the deployable energy absorber (DEA), uses an expandable Kevlar honeycomb to dissipate kinetic energy through crushing. The DEA incorporates a unique flexible-hinge design that enables the honeycomb to be packaged and stowed efficiently until needed for deployment. Experimental evaluation of the DEA included dynamic crush tests of multicell components and vertical drop tests of a composite fuselage section retrofitted with DEA blocks onto multiterrain. Finite-element models of the test articles were developed and simulations were performed using the transient dynamic code LS-DYNA. In each simulation, the DEA was represented using shell elements assigned two different material properties: Mat 24, an isotropic piecewise linear plasticity model, and Mat 58, a continuum damage mechanics m...

Quasi-static and dynamic experiment investigations on the crashworthiness response of composite tubes

Crashworthiness performance of carbon and glass composite tubes have been comprehensive investigated under quasi-static and dynamic axial crush testing. In this study, collapse modes and specific energy absorption (SEA) of different ply orientation of carbon fabric composites and unidirectional glass tubes were analyzed. For the weaker tensile strength and bending strength of glass composites, crack propagated approximately perpendicular to the fiber direction when the ply angle was small. Large amount of fibers breakage made the specific energy absorption over 80 kJ/kg under dynamic load. Thickness effect had inverse influence on SEA under different impact rate. The specific energy absorption declined as tube thickness increased under dynamic crush tests, however, increased under quasi-static tests. Hybridization of glass/carbon tubes and carbon/carbon composites were analyzed by increased the axial fiber content. It was found that hybridization tubes of G803/3234 fabric and G827/3234 axial tapes with higher G827/3234 content present excellent energy-absorption capability under dynamic and quasi-static tests for all specimens tested. POLYM. COMPOS., 34:1099–1109, 2013. © 2013 Society of Plastics Engineers

Historical background: early deliberations on and assessments of need for dynamic crush test

AbstractBeginning in the late 1970s, discussions were fostered by the International Atomic Energy Agency (IAEA) on the need for additional tests for some type B packages. Consideration at the international level of these early deliberations and tests ultimately led to the inclusion in the IAEA Regulations for the Safe Transport of Radioactive Material of the third mechanical (drop) test for demonstrating the ability of the package design to withstand accident conditions of transport, commonly known as the ‘dynamic crush test’. This test included the requirement that the package be positioned so as to sustain maximum damage. Recently discussions have been occurring as to what constitutes positioning on an unyielding target, where considerations are being put forward for clarifying this phrasing and possibly changing the test requirement. Some of these proposed changes could make the test more demanding than originally envisioned. This paper, developed in support of a panel discussion at PATRAM 2010, provid...

Crush testing at Oak Ridge National Laboratory

The dynamic crush test is required in the certification testing of some small type B transportation packages. International Atomic Energy Agency regulations state that the test article must be ‘subjected to a dynamic crush test by positioning the specimen on the target so as to suffer maximum damage’. Oak Ridge National Laboratory Transportation Technologies Group performs testing of type B transportation packages, including the crush test, at the National Transportation Research Center in Knoxville, TN, USA. This paper documents ORNL’s experiences performing crush tests on several different type B packages.

When is a crush test not a crush test? or What constitutes a valid crush test?

Recent discussions at the international level are elaborated regarding the intent and method for clarifying acceptable package/drop mass orientations for the dynamic crush test that is required for some Type B and some Type A fissile radioactive material packages. Coverage includes part of the discussions that occurred at an International Atomic Energy Agency Consultants Services Meeting convened to discuss this issue in September 2008.

Finite element mesh design of a cylindrical cask under puncture drop test conditions

Transport casks for radioactive materials have to withstand the 9 m drop test, 1 m puncture drop test and dynamic crush test with regard to the mechanical requirements according to the IAEA regulations. The safety assessment of the package can be carried out on the basis of experimental investigations with prototypes or models of appropriate scale, calculations, by reference to previous satisfactory safety demonstrations of a sufficiently similar nature or a combination of these methods. Computational methods are increasingly used for the assessment of mechanical test scenarios. However, it must be guaranteed that the calculation methods provide reliable results. Important quality assurance measures at the Federal Institute for Materials Research and Testing are given concerning the preparation, run and evaluation of a numerical analysis with reference to the appropriate guidelines. Hence, a successful application of the finite element (FE) method requires a suitable mesh. An analysis of the 1 m puncture ...

Static and Dynamic Crushing Behaviors of Aluminum Foam

Quasi-static and dynamic axial crushing tests were carried out to investigate the energy absorption capacity of aluminum foam with several densities. First, aluminum foam samples with three densities were crushed quasi-statically to study their compression characteristics, the stress strain relationship curves and energy absorption capacities were achieved from the test results; then dynamic crushing tests were carried out to check the crushing behaviors of the corresponding samples; finally, the energy absorption capacities of tested samples were compared. According to the tests results, all the aluminum foam samples showed very good isotropy and very high mass specific energy absorption capacities. For the crushing tests, the dynamic crushing behaviors were very similar to the static ones, which meant aluminum foam was insensitive to the crash velocity tested.

경수로 핵연료집합체 지지격자체의 횡방향 충격강도 연구

지지격자체는 경수로 핵연료집합체의 가장 중요한 핵심 구조부품 중에 하나이다. 질칼로이 지지격자체 설계시의 우선적으로 고려해야 할 사항은 지지격자체가 원자로심에서 냉각수의 심한 수두손실을 유발하지 않으면서 지진사고를 고려한 설계하중 하에서 충분한 횡방향 충격강도를 갖도록 하는 것이다. 본 연구에서는 시험과 유한요소해석을 통해 지지격자체의 횡방향 충격강도에 영향을 주는 인자들에 대한 분석을 수행하였고, 지지격자체 제조용 질칼로이 원자재 소요량을 획기적으로 줄이면서 지지격자체의 횡방향 충격강도를 개선할 수 있는 방안을 제시하였다.

IMPACT ANALYSIS AND TEST FOR THE SPACER GRID ASSEMBLY OF A NUCLEAR FUEL ASSEMBLY

A spacer grid assembly is one of the main structural components of the nuclear fuel assembly for a Pressurized light Water Reactor (PWR). The spacer grid assembly supports and aligns the fuel rods, guides the fuel assemblies past each other during a handling and, if needed, sustains lateral seismic loads. The ability of a spacer grid assembly to resist these lateral loads is usually characterized in terms of its dynamic and static crush strengths, which are acquired from tests. In this study, a finite element analysis on the dynamic crush strength of spacer grid assembly specimens is carried out. Comparisons show that the analysis results are in good agreement with the test results to within about a 30 % difference range. Therefore, we could predict the crush strength of a spacer grid assembly in advance, before performing a dynamic crush test. And also a parametric study on the crush strength of a spacer grid assembly is carried out by adjusting the weld penetration depth for a sub-sized spacer grid, which also shows a good agreement between the test and analysis results.

Dynamic crush behaviors of aluminum honeycomb specimens under compression dominant inclined loads

The dynamic crush behaviors of aluminum 5052-H38 honeycomb specimens under compression dominant inclined loads are investigated by experiments. Different types of honeycomb specimens were designed for crush tests under pure compressive and compression dominant inclined loads with respect to the out-of-plane direction. A test fixture was designed for dynamic crush tests under inclined loads. The results of the dynamic crush tests indicate that as the impact velocity increases, the normal crush strength increases and the shear strength remains nearly the same. The trends of the normalized normal crush strengths under inclined loads for specimens with different in-plane orientation angles as functions of the impact velocity are very similar to each other. Based on the experimental results, a macroscopic yield criterion as a function of the impact velocity is proposed. The experimental results suggest that, as the impact velocity increases, the shape of the macroscopic yield surface changes, or more specifically, the curvature of the yield surface increases near the pure compression state. The experimental results also show similar microscopic progressive folding mechanisms in honeycomb specimens under pure compressive and inclined loads. However, honeycomb specimens under inclined loads show inclined stacking patterns of folds due to the asymmetric location of horizontal plastic hinge lines.

Design and certification of a composite thin-walled structure for energy absorption

Thin-walled Carbon Fibre Reinforced Polymer (CFRP) energy-absorbing devices have been successfully used in premier racing leagues to drastically improve the crashworthiness of a vehicle. Since their introduction in Formula 1 (F1) in the second half of the 1990s, the Rear Impact (RIMP) attenuators have received particular attention and their utilisation has been documented in scholarly publications. The engineering development and certification of the RIMP of the Star Mazda Racecar is discussed in detail. Quasi-static and dynamic crush tests are performed on two RIMP designs, featuring very different stacking sequences, are experimentally investigated. While the overall behaviour is quite different, they both exhibit the ability to collapse in a stable, progressive fashion. Furthermore, although the overall shape of the load-stroke diagram, energy absorption characteristics and failure behaviour have shown very good agreement, the quasi-static test results tend to substantially overestimate the effective dynamic energy absorption characteristics. The final RIMP design is selected based on its higher energy absorption and friendlier manufacturing characteristics.

Crashworthiness of straight section hydroformed aluminium tubes

There exists considerable motivation to reduce vehicle weight through the adoption of lightweight materials, such as aluminium alloys, while maintaining energy absorption and component integrity under crash conditions. The interaction between tube hydroforming and behaviour during crash events was studied using lightweight automotive structural members. Dynamic crush tests were performed on 400 mm length sections of both non-hydroformed and hydroformed EN-AW 5018 aluminium alloy tubes. The force versus crush distance data from 76.2 mm diameter non-hydroformed tubes was compared with results from 76.2 mm square cross-section hydroformed tubes of 2.0 and 3.5 mm initial tube thicknesses. The hydroforming operation was performed using a high-pressure process in which the corner radius of the tube cross-section was varied. Explicit dynamic finite element simulations of the hydroforming and crash events were carried out with particular attention to the transfer of forming history from the hydroforming simulations to the crash models. The values of the tube thickness, work hardening, residual stress, and damage level at the end of the hydroforming simulation were used as the initial state for the crash model. The Gurson–Tvergaard–Needleman constitutive model was used to account for damage based on void nucleation, growth, and coalescence. Numerical predictions of the force versus crush distance response were compared to experimental data. The results have demonstrated that it is important to account for thickness changes and work hardening from previous forming operations, in simulating crash events. The energy absorbing capabilities of the hydroformed aluminium tubes decreased with sharper corner radius due to increased thinning of the material during the hydroforming process. It was found that the simulations slightly over-predicted the mean crush force compared to the experimental data.