Crush Load Research Articles

Highly efficient preparation of Li2O breeder materials with core‐shell structure by oil‐based granulation route

AbstractThis paper gives an oil‐based granulation approach to realize the efficient preparation of Li2O breeder materials, which solve the problems of long preparation cycle, high manufacturing cost and difficult to be homogenization and densification in the past. Li2O precursor spheres with narrow size distribution and uniform spherical shape can be obtained using paraffin oil as binders. The Li2O feed powder with bimodal size distribution will self‐organize to form a core‐shell structured sphere during granulation, in which the core and shell are composed of small particles and large particles, respectively. Notably, the Li2O ceramic spheres sintered at 900°C can achieve a crush load of 40.69 ± 4.01 N and a theoretical density of 79.66% TD, which was not achievable by the methods reported in the previous literature. The strategy proposed in this work not only can be easily extended to other material systems but also opens up a new avenue for the design and preparation of tritium breeder materials with uniform size distribution and satisfactory mechanical properties.

Crashworthiness analysis of multi-configuration thin walled co-axial frusta tube structures under quasi-static loading

Abstract In the present study crashworthiness performance of monolithic and co-axial multi-wall (double, triple, and four layered) frusta tube structures was investigated under the quasi-static axial loading. The developed layered frusta tubular structures having a total equivalent thickness of 2.3 mm were made of aluminium alloy AA-1080 sheet. A series of layered configurations were simulated and analysed using non-linear finite element analysis code LS-DYNA, keeping volume approximately the same as the monolithic frusta tube. For the effectiveness of the simulated results, double-tubular structure was examined through experimental results. A parametric study was performed by keeping taper angle constant as 5.71° with the variation in height (91.6 and 82 mm for double layered, 91.6, 86 and 78 mm for triple layered and 91.6, 87, 82 and 77 mm for four layered), thickness (2.3–0.4 mm) and diameter (smaller end diameter in the range of 42.8 mm–48.4 mm while larger end diameter varied from 61 mm to 64 mm) to analyse the crushing performance of layered structures. The crashworthiness performance indicator like peak force (PF), mean force (MF), energy absorbing capacity (EAC), specific energy absorption (SEA) and crush load efficiency (CLE) which is defined as the ratio of MF to the PF, were studied for the various layered frusta tubular structures. Moreover, optimization technique GRA (Grey Relational Analysis) was employed to obtain a better combination of multi-wall layered structures. With the increase in the layer, the initial peak force was reduced compared to the monolithic frusta. The optimization technique suggested the triple-layer configuration showed better crashworthiness performance.

Preparation of Li4SiO4 pebbles with increased lithium content and crush load via molten salt assisted sintering

Improving the lithium density and performance of lithium-based ceramics is the main direction for the development of advanced tritium breeder. In this work, the previously used polymers or organics were replaced by eutectic LiNO3–LiCl in wet process for preparing spherical green body, and then Li4SiO4 pebbles were fabricated through molten salt assisted sintering. The eutectic salt used herein was eco-friendly and had little effect on the Li4SiO4 pebbles. Instead, the incorporation of eutectic salt improved the lithium density and sinterability of Li4SiO4. The prepared Li4SiO4 pebbles exhibited well-grained microstructure, and the grain size increased with the increasing contents of eutectic salt. Compressive tests showed that the crush load increased more than five times when 20 wt% eutectic salt was added. The proposed method may have great prospects in the preparation of tritium breeding materials.

Crashworthiness analysis and optimization of different configurations multi-layered corrugated sandwich panels under crush loading

Multi-layered corrugated sandwich panels can be made up of different core shapes, different arrangements, the variable height, and variable thickness in every layer. In this paper, the crashworthiness behaviors of multi-layered corrugated sandwich panels with different configurations, which are controlled by these four factors, are analyzed and compared. The optimal configuration is found by adopting orthogonal experimental design and range analysis method. A novel multi-layered corrugated sandwich structure with functionally graded thickness is proposed and studied and is proved to better structural crashworthiness. First, finite element models of multi-layered corrugated sandwich panels are established and validated by experiment. Then, the effect of the four factors with three levels on crashworthiness is analyzed, and we obtain the main factor and the optimal configuration with the maximum specific energy absorption by using orthogonal experimental design and range analysis method. Finally, parametric studies and multi-objectives optimization of the proposed novel multi-layered corrugated sandwich structure with functionally graded thickness are conducted. The optimization is aimed at maximizing the specific energy absorption and minimizing the initial peak force under crush loading, based on the non-dominated sorting genetic algorithm and response surface method technique. These findings can provide valuable guidelines for the design of multi-layered corrugated sandwich panels with different configurations under crush loading.

Investigation on the temperature dependent out-of-plane quasi-static compressive behavior of metallic honeycombs

Abstract This study investigates the effect of temperature on the out-of-plane quasi-static compressive behavior of metallic honeycombs by numerical and theoretical methods. Adopting a temperature dependent elastic-perfectly plastic constitutive relation, the temperature dependent out-of-plane quasi-static compressive mechanical performance of Al5052 honeycomb is studied with the finite element method. The results show that the plateau stress, peak stress and specific energy absorption (SEA) of Al5052 honeycomb decrease gradually with increasing temperature, while the crush load efficiency (CLE) and deformation pattern are temperature insensitive. Then, based on the numerical results in this study and super folding element theory, the temperature dependent theoretical models without fitting parameters for the plateau stress and SEA of metallic honeycombs are developed, respectively. These theoretical models are successfully verified against numerical simulations and experiments. Based on these theoretical models, the effects of parent material properties on the plateau stress and SEA at different temperatures are discussed. The results in this study provide useful guidelines in optimizing the choice of parent materials to fabricate metallic honeycombs with better energy absorption efficiency at different temperatures.

Properties of ceramic pebbles prepared by melt spraying

In this study, ceramic pebbles were prepared via a melt spraying method and their properties were systematically characterised. The average particle diameter, sphericity, grain size, specific surface area, and density of the ceramic pebbles prepared by melt spraying were 1.28 mm, 1.01, 2292.92 nm, 6.42 m2/g, and 95.1 %TD, respectively. The amount of Li loss was 3.7055%. A thermal cycle test was conducted, and it was found that the pebbles could withstand fifteen hot–cold cycles. The crush load of the pebbles after heat treatment was 21.6259 ± 5.6282 N. The performance of the ceramic pebbles prepared by melt spraying was compared to that of ceramic pebbles prepared by other methods, and the pebbles prepared via a melt spraying exhibited better properties. The results show that the ceramic pebbles prepared by melt spraying exhibited favourable properties.

Elastic response of individual European advanced ceramic breeder pebbles during uniaxial compression

Lithium orthosilicate (Li4SiO4, LOS) based advanced ceramic pebbles are currently the reference material in Europe for solid tritium breeder blankets. These breeder pebbles, as the constituent of pebble beds, are not structural members but undergo cyclic thermo-mechanical compression. To withstand these operational loads, lithium metatitanate (Li2TiO3, LMT) was added as a second strengthening phase during their development at Karlsruhe Institute of Technology (KIT) in the Institute for Applied Materials Energy Storage Systems (IAM-ESS). To capture the micro scale response of the pebble bed, Discrete Element Modelling (DEM) is currently used. These simulations use the Hertzian contact model and require the crush load and Young's modulus of individual pebbles as input. In this study uniaxial compression tests were done to obtain the mechanical response of individual 500 μm and 1000 μm diameter pebbles produced by the KALOS facility built and installed at KIT IAM-ESS. Correcting the Hertzian equation to account for pebble defects, the Hertzian contact assumption was validated. The crush load increased with LMT content but the Young's modulus appeared to be independent of the LMT content. The closed porosity prevalence and variation across various batches is low and did not show any influence on the crush strength or stiffness of the pebbles.

Effect of cut-outs on the axial crushing response of cap and open-end hybrid frusta tube

The present paper presents the computational analysis of the crushing response of AA-1080 cap and open end hybrid frusta tube, with and without circular cut-outs subjected to the quasi-static axial loading. The two concentric frusta tubes placed co-axially having different heights of 91.6 mm and 85 mm of inner and outer tubes respectively were considered as hybrid frusta. The frusta tubes thickness and semi-apical angle were assigned constant value as 1.15 mm and 5.71˚ respectively. The effect of radial distance (2.94 mm, 4.44 mm, and 6.94 mm) between two concentric tubes as investigated. The numerical simulations were carried out using finite element code LS-DYNA.The crushing behavior of hybrid frusta tubes was examined based on the response of the peak force (PF), mean force (MF), crush load efficiency (CLE), and energy absorbing capacity (EAC). The radial distance was found to have a major impact on the deformation behaviour and with an increase in radial distance, the CLE decreases. Moreover, the response of cut-outs on the performance of hybrid frusta was presented and analysed. Through having a cut-out on both sets of hybrid frusta, the CLE increased by 3% to 10% whereas the radial distance R3 was insignificant as per CLE perspective. Further, the reduction in PF was found 13% to 23% for cap end while 8% to 19% for open end hybrid frusta.

Influence of Simulation Parameters in the Combined Loading Compression Testing of CFRP Specimens

In this paper a sensitivity study of a FEM model representing a carbon/epoxy composite material tested in Combined Loading Compression (CLC) is presented and the results are compared to experimental results. The present study aims to simulate the failure of composite materials when subjected to compression and crush loading conditions. This is required as a first step of a Building-Block Approach towards full-scale modelling of complex structures.In the experimental part of the work, a laminate panel was manufactured with carbon unidirectional prepreg (Deltapreg UTS-300-DT120-37EF) in a cross-ply, balanced and symmetric stacking sequence, cured in autoclave at 120°C and 5 bar for 90 min. A number of six samples, extracted from the panel, were tested in compression following ASTM D6641/D6641M-16.Numerical simulations have been implemented by means of the commercial software, ESI-VPS PAM CRASH. Boundary conditions, specimens’ dimensions and material properties emulated real test conditions. A sensitivity study was performed on critical simulation parameters: the effect of mesh size and number of shell surfaces representing the composite stacking sequence was initially investigated. Furthermore, the specimen failure mode was inspected by the application of TIED links between the composite plies. Numerical results have been compared with experimental data and the comparison provided references for testing scale-up in the Building-Block Approach.

An experimental study on performance of jute‐polyester composite tubes under axial and transverse impact loading

AbstractThe efficacy of woven jute‐polyester (JP) composite tubes as structural energy‐absorbing countermeasures has been explored in the current study. In this connection, the behaviors of 3‐ply and 4‐ply JP composite tubes of square and double‐hat shaped sections subjected to axial quasi‐static and impact loads are considered, and compared with 4‐ply glass‐polyester (GP) tubes of similar geometric configurations. Initially, basic mechanical characterization of JP laminates is carried out using a Universal Testing Machine, which is followed up with axial quasi‐static and drop‐weight impact testing of JP tubes, along with similar tests carried out on GP tubes. A thorough comparison is made between the performances including failure patterns of JP and GP components under axial loading using metrics such as peak load, mean crush load, absorbed energy, and specific energy absorption (SEA). As many structural applications involve dynamic bending loads, a comparative study is carried out between double‐hat JP and GP components subjected to transverse impact loading. Based on the competitive values of mean load and SEA yielded by jute‐composite tubes in the present study for axial impact loading, and high mean load and moderate energy absorption till failure recorded by similar components under three‐point impact bending, it can be concluded that JP tubes can be capable of supporting impact loads under both axial and bending modes.

Characterization of tritium breeding ceramic pebbles prepared by melt spraying

Li4SiO4 and Li2TiO3 have long been recognized as two excellent promising tritium breeding materials. In this paper, two kinds of ceramic pebbles, Li4SiO4 pure phase ceramic pebbles and Li4SiO4-xLi2TiO3 multiphase ceramic pebbles were prepared by a melt spraying method at a superheating temperature of 100 ℃ and then tested for their performance. The proportion of pebbles with a particle diameter of 0.8∼1.2 mm reached the maximum of 24.02 % when the spraying pressure is 0.04 MPa. The surface of the pebbles prepared by the spraying method was smooth, and the surface roughness was reported for the first time to reach 2.039 μm. The sphericity reached 1.027. When the Ti/Si molar ratio was 0.5, the crush load of the pebbles after heat treatment reached 71.6 N and the thermal conductivity of the materials reached its maximum of 3.098 W/(m·K) at 700 ℃.

Air-blast loading on empty metallic beverage can used as sacrificial cladding: Experimental, analytical and numerical study

The aim of this work is to study the response of a sacrificial cladding using metallic beverage can (MBC) as crushable core. A single MBC axially crushed is considered. An adequate experimental set-up is developed to examine the collapse pattern, the mean crush load and the absorption capacity of a single MBC under a blast load. A comparison with low velocity impact is discussed. The effect of both the entrapped gases inside the MBC and the crush velocity are investigated through analytical and numerical studies. A clear loading rate dependency of the mean crush load is observed. It varies from 0.94 kN to 1.35 kN by increasing the front plate velocity from 17 m/s (FP3) to 44 m/s (FP1). The effect of the entrapped gases inside the MBC structure increases the mean crush load, and, then, the transmitted load to the main structure. In addition to the dynamic material properties, the entrapped gases are considered for an accurate prediction of the mean crush load. Good correlation with the experimental results is observed.

Crashworthiness performance of hybrid kenaf/glass fiber reinforced epoxy tube on winding orientation effect under quasi-static compression load

This research was aimed to study the effect winding orientation on the crashworthiness performance of hybrid tube. The specimens tested under quasi-static compression load involve of three winding parameters (θ = 30°, 45° and 70°) of hybrid kenaf/glass fiber reinforced epoxy and glass fiber reinforced epoxy as contrast specimen. The automated filament winding technique has been used in fabrication of hybrid and non-hybrid composite tube and crashworthiness performance was investigated experimentally. The effects of winding orientation on energy absorption capabilities and crashworthiness characteristic were investigated through quasi-static compression load and the result are compared with the glass fiber composite tube to justify the capability of hybrid natural/synthetic as energy absorption application. Hybridized samples proved to enhancing the progressive crushing capability as combination of local buckling, delaminate and brittle fracturing as progressive crushing modes.In the view of winding orientation aspect, the results of high winding orientation of hybrid composite tube elevated the crush load efficiency, specific energy absorption and energy absorption capability compared to glass composite tube (GFRP). The hybrid kenaf/glass composite tube with high winding orientation showed the best winding orientation to enhance the energy absorber characteristics as energy absorption application.

A novel mass production method for Li2TiO3 tritium breeder ceramic pebbles using polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) assisted granulation method

A novel mass production method of lithium titanite (Li2TiO3) tritium breeder ceramic pebbles using polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) assisted granulation method (APG) was proposed. A binder solution of polyvinyl alcohol (PVA) was used to modify the Li2TiO3 precursor powder. The powders with adhesive properties were prilled to form green pebbles (GPs) by spheronization at a low rotation speed and spraying with polyvinyl pyrrolidone (PVP), in several cycles. Then, the density and the crush load of the GPs were improved by high-speed rolling. Finally, the ceramic pebbles were produced by sintering. The phase, the microstructure, and the crush load of the ceramic pebbles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and with a universal tester, respectively.

Quasi-static crush modelling of carbon/epoxy composites with discontinuous Galerkin/anisotropic extrinsic cohesive law method

Carbon/epoxy composites demonstrate significant promising improvements of weight to performance in the automotive industry. However, the design of carbon/epoxy composite components for crashworthiness remains challenging and normally requires laborious and repeated experimental work. This study adopts a predictive crush model of carbon/epoxy composites, which can partially replace the experimental work. The discontinuous Galerkin (DG) method with extrinsic cohesive laws is employed to simulate the failure patterns in the composite structures. The application of DG distinguishes the fracture model from the conventional approach where preset cohesive elements are used on the location where cracks are expected. The mixed mode cohesive laws are used to simulate the delamination between each layer. To capture different crack propagations in different layups, the anisotropic cohesive law is used to simulate the intralaminar crack propagation in composites. To verify the adopted model, circular composite tube specimens with different layups have been simulated and compared with tests under quasi-static crush loadings. The comparisons of numerical results with experimental data show that the DG crush model can reproduce the experimental results with relatively high accuracy.

Synthesis, characterization and sintering of Li2TiO3 nanoparticles via low temperature solid-state reaction

Synthesis of fine Li2TiO3 powders via low-temperature solid-state reaction (LTSSR) was studied. Solid Li2CO3 and H2TiO3 were blended by planetary ball mill with deionized water as medium. Calcination of the milled powder at low temperature of 500 °C resulted in the formation of pure Li2TiO3 nanoparticles. Another Li2TiO3 powder was also prepared by the conventional solid-state reaction (SSR) and a good comparison between different routes was realized. The results show that the particle size of LTSSR powder is significantly decreased to 19.6 nm while the one obtained by SSR is 146.6 nm. Low temperature calcined powders have less agglomeration and higher sinterability, which can be sintered at lower temperature. Pebbles sintered from the LTSSR powders at 750 °C exhibit small grain size (650 nm), high relative density (85.1%) and satisfactory crush load (42.8 N), whereas the SSR pebbles can only be sintered above 950 °C with the relative density close to 80%. Besides, the LTSSR samples also have a higher conductivity at room temperature, indicating the lower tritium diffusion barrier in ceramics. It is confirmed that H2TiO3 rather than TiO2 is more appropriate for the solid-state reaction to produce Li2TiO3 powders with nano-size particles and favorable properties.

Mechanical strength stability of tritium breeding materials under high temperature deuterium conditions

The mechanical strength of solid tritium breeding materials is one of the key factors for D-T fusion reactors. The crushing of ceramic breeder pebbles will block both tritium recovery circuit and thermal transmission. The mechanical strength changes of Li4SiO4 and Li2TiO3 pebbles exposed to high temperature and hydrogen isotope atmosphere were investigated. The crush load of Li4SiO4 decreased to 66 % of the original values when the breeders were exposed in deuterium gas at the temperature higher than 750 oC. Nevertheless, the crush load of Li2TiO3 remained stable at all the designated temperatures. Investigations involving phase analysis, defect analysis, grain size analysis, and lithium content analysis were performed to determine the causes of mechanical strength change. No new phase formation and no obvious lithium decrease were demonstrated by X-ray diffraction (XRD) and Inductively Coupled Plasma - Atomic Emission Spectrometer (ICP-AES). Defects arising from reduction reaction didn't play an important role in mechanical strength reduction. The main reason responsible for the decrease of mechanical strength of Li4SiO4 was attributed to grain growth. The grain growth behavior was understood by grain growth kinetics. The kinetic parameters of grain boundary migration for Li4SiO4 pebbles were obtained as n of 4 and activation energy Q of 140 kJ/mol. The mechanism of grain growth was given to demonstrate the mechanical strength change of ceramic breeder pebbles.

Experimental investigation of energy absorption behaviour of circular carbon/epoxy composite tubes under quasi-static and dynamic crush loading

Carbon/epoxy composites demonstrate significant and promising improvements of the weight-to-performance ratio in the automotive industry. In this paper, their energy absorption performance is thoroughly investigated. Quasi-static and dynamic axial crush tests have been performed on a variety of carbon/epoxy composite tube specimens with different thicknesses, layups and architectures (fabric and unidirectional). It is shown that the frequency response of the drop weight test setup bias the crush load histories and give false peak crush loads which lead to a wrong understanding of the elastic behaviour of the composites. Different filtering processes are adopted to investigate their necessity and influence on the energy absorption performance of carbon/epoxy composites. Comparing the specific energy absorption and crush efficiency of the variety of carbon/epoxy composite tube specimens, the fabric ones perform better than the unidirectional ones. The results show that more energy can be absorbed in the quasi-static conditions.

Preparation of porous Al2O3 ceramic microspheres by a novel micro-droplet jetting rapid forming method

Porous Al2O3 ceramic microspheres were prepared by a novel micro-droplet jetting rapid forming method using a polyvinyl alcohol (PVA) solution as a binder and a boric acid as a curing agent. The droplet jetting and slurry curing procedures are mainly responsible for the uniformity and production rate of the Al2O3 ceramic microspheres during this novel method. A slurry with a PVA content of 3 wt % and a solid loading of 45 vol % exhibited a high solid loading and a low viscosity, and it was suitable for the droplet jetting process. The curing process was determined by the cross-linking reaction between the boric acid and PVA, and the Al2O3 ceramic microsphere green bodies had a good and stable formability with a boric acid content of 10 wt %. The size of sintered Al2O3 ceramic microspheres with a good sphericity was precisely controlled in a small range. Furthermore, the sintering temperature had a significant effect on the performance of the Al2O3 ceramic microspheres. With a sintering temperature of 1400 °C for 3 h, the Al2O3 ceramic microspheres with a uniform microstructure were obtained, exhibiting superior performances that include a grain size below 5 μm, a sintered shrinkage of 6.67%, a relative density of 82.1%, an open porosity of 10.6% as well as a crush load of 76 N.

Low-temperature fabrication of Li2O porous ceramic pebbles by two-stage support decomposition

In this study, Li2O porous ceramic pebbles were synthesized by decomposing the xLi2CO3-yLiNO3 precursor pebbles at low temperature. This efficient decomposition reaction was mainly attributed to the two-stage support decomposition of Li2CO3 and LiNO3. The results indicated that the molar ratio of Li2CO3 and LiNO3 will directly affect the phase composition, pore structure and crush load of sintered pebbles. The high-purity Li2O ceramic pebbles sintered from Li2CO3–LiNO3 precursor pebbles at 730 °C exhibits the open porosity of 24.8 ± 0.7%. The crush load of the ceramic reaches 21.18 ± 1.38 N although the structure was porous. The Li2O porous ceramics fabricated in this study will have potential application in tritium breeder materials.