Crush Load Research Articles

Fast fabrication of high quality Li2TiO3–Li4SiO4 biphasic ceramic pebbles by microwave sintering: In comparison with conventional sintering

Abstract A comparative study between the microwave and conventional sintering of Li2TiO3–Li4SiO4 biphasic ceramic pebbles was systematically performed. Comparing to samples sintered by conventional method, the microwave sintered samples exhibited homogeneous microstructure with uniform grain size distribution. In addition, the microwave sintered samples showed higher relative density (86.0% T.D.) and crush load (22.7 N). The results indicated that the microwave sintering process is a prospective method for fabricating Li2TiO3–Li4SiO4 biphasic ceramic pebbles with excellent mechanical performance as tritium breeder materials.

Low-cost fabrication of Li2TiO3 tritium breeding ceramic pebbles via low-temperature solid-state precursor method

Abstract Lithium metatitanate (Li2TiO3) ceramic pebbles were fabricated from the powder synthesised via low-temperature solid-state precursor method. Solid H2TiO3 and LiOH·H2O react chemically during ball milling process to form a nano-sized precursor powder. Pure β-Li2TiO3 powder can be obtained by calcining the precursor powder at 500 °C, which is half the temperature of conventional solid-state method. The synthesis process is simple and low-cost, which would be more available to achieve batch production among all feasible techniques. The low-temperature calcination will effectively avoid hard particle aggregates and poor sinterability caused by high-temperature heat treatment, which is conducive to prepare ceramics with good properties. The results show that the powder exhibits high sinterability with small particle size of 19 nm. The Li2TiO3 ceramic pebbles sintered at 800 °C have small grain size (470 nm), high relative density (83%) and good crush load (45 N), which has great potential as tritium breeding materials for fusion reactors.

Crashworthiness optimization of front rail structure using macro element method and evolutionary algorithm

In this paper, the research on crashworthiness optimization of thin-walled structures is presented. The model of “S”-shaped frame subjected to complex crush load is analyzed. The objective of the study is to determine the optimal dimensions of the space frame cross section so as to achieve the maximal energy absorption of the structure and to fulfill the design requirements related to the crushing force value and the geometry relationship. The Visual Crash Studio (VCS) software, based on the macro element methodology, is used to simulate the response of a thin-walled beam during the impact and to determine crashworthy parameters. The results present a very good correlation with the finite element calculations but can be obtained in a much shorter time. The VCS software was coupled to evolutionary algorithm developed to determine the best solution. The optimization procedures revealed the necessity of a new design criterion related to maximal bending moments in the structure. This formulation enabled to obtain very good results after short processing on a PC computer. The proposed approach may be successfully used at early stages of the crashworthiness analysis.

Low-temperature preparation of nanostructured Li2TiO3 tritium breeder ceramic pebbles using CTAB-modified ultrafine powders by a mixed solvent-thermal method

Effects of cetyl trimethyl ammonium bromide (CTAB) on the formation of Li2TiO3 nanocrystals during ethanol-water solvothermal reactions were investigated. Addition of CTAB changed Li2TiO3 crystalline morphology from large to small aggregate particles due to the steric repulsion and electrostatic interaction of the CTAB ligands. Aggregate particle size of the Li2TiO3 precursor was reduced from 455.2 to 138.7 nm by preventing their agglomeration after CTAB addition. This was followed by sintering the green body prepared with the CTAB-modified precursor powders using an indirect wet method, then the nanostructured Li2TiO3 ceramic pebbles were obtained at relatively low temperatures from 750 to 800 °C for 4 h. Nanostructured Li2TiO3 ceramic pebbles had small grains and a large number of grain boundaries, which might potentially improve the radiation tolerance, tritium release rate, and mechanical properties of Li2TiO3 tritium breeder pebbles. In addition, grain growth mechanisms as function of different sintering temperatures, crush load as well as relative density of fabricated nanostructured Li2TiO3 ceramic pebbles were also investigated.

Crushing analysis and multi-objective optimization of different length bi-thin walled cylindrical structures under axial impact loading

ABSTRACTThis article attempts to increase the crashworthiness characteristics of energy absorbers. It is found that the effect of the bi-tubular arrangement on the energy absorption and peak force is nonlinear. This nonlinearity is somewhat related to friction but is mostly related to the changing of buckling modes. Therefore, it is possible to reach higher Specific Absorbed Energy (SAE) in the bi-tubular case than with two tubes since the weight is the same in both arrangements while the energy absorption is higher in the bi-tubular case. To exploit this, multi-objective optimization of bi-thin walled cylindrical aluminium tubes under axial impact loading is performed. The absorbed energy and the SAE are considered as the objective functions while the maximum crush load is regarded as a constraint. Finally, the optimal dimensions of tubes are found in order to maximize the SAE and energy absorption for a specified maximum crushing force.

Influence of titanium sources on the microstructures and properties of Li2TiO3 ceramics prepared by hydrothermal method

The influence of titanium sources on the microstructures and properties of Li2TiO3 were investigated. The results show the hydrothermal synthesized α-Li2TiO3 is a metastable phase and would transform into β-Li2TiO3 phase during sintering. Compared with TiO2-hydrothermal synthesized powder, the TBT synthesized powder has better sintering activity. The relative density of ceramic pebbles can reach 84% when it was sintered at 800 °C for 3 h. The grain size and crush load are 0.62 μm and 35 N, respectively. The formation mechanisms during hydrothermal process are also discussed. Combined results of XRD and TEM, it is concluded that for TiO2 as titanium source, TiO2 particles first dissolve into the LiOH solution and then the dissolved TiOx− groups react with Li+ to form Li2TiO3 precipitates. While for TBT source, α-Li2TiO3 nucleus immediately form as soon as TBT is added into the LiOH solution at room temperature.

Fabrication of Li4SiO4-Li2ZrO3 composite pebbles using extrusion and spherodization technique with improved crush load and moisture stability

The effect of different amount of Li2ZrO3(LZ) (0-15wt%) addition on the properties of composite Li4SiO4 (LS) ceramic pebbles was studied. The Li4SiO4-Li2ZrO3 composite powder was prepared using solid state route at a calcination temperature as low as 900 °C via in-situ method. The composite pebbles were fabricated using a cost-effective and simple technique called extrusion-spherodization. The sintered pebbles were characterized for density, grain size, pore size distribution, crush load and moisture stability. The composite pebbles showed good sintered density (∼87.1%) for LS-5wt% LZ in comparison to LS pebbles (∼80%) when fired at 1000 °C. Moreover, the LS grain size in the composite pebble was significantly reduced by ∼19.7% when compared to LS pebbles. We also found that the average crush load value of the LS-5wt% LZ composite pebbles was improved by nearly 77% (30 N) to that of the pure LS pebbles (17 N). The LS-5wt% LZ pebbles showed excellent stability to moisture in terms of phase and mechanical crush load retention after 30 days of exposure to humidity. The results achieved in this work were found to be fit to the desired properties for use as a ceramic solid breeder.

Commuter travel cost estimation at different levels of crowding in a suburban rail system: a case study of Mumbai

This research values travel attributes such as waiting time, in-vehicle time and crowding levels using behavioural data obtained from Mumbai local train commuters through a stated preference experiment. Actual on-board crowding images are considered to perceive the crowding more realistically by the train users. A multinomial logit modelling technique is used for estimating commuter travel cost (time) at different crowding levels. Results show that there is an increase in perceived in-vehicle travel time with the increase in crowding level. Traveling in a crowded seating condition increases the travel cost by 0.81 min per 1 min travel. A crowded seat leads the user to perceive an 81% increase in in-vehicle travel time, whereas this perception increases by 282% more during travel in super dense crush crowding compared to normal travel conditions. The generalized travel cost increases to a maximum in the super dense crush crowding. An effect analysis was carried out to understand the sensitivity of gender, age, income, and trip length on travel attributes. Female users tend to perceive more decrease in utility due to crowding than male users. A reduction of 60% in seating capacity will lower the perceived travel cost per minute by 43% during peak hours of travel. Essentially, a reduction in seat capacity will increase the standee capacity which in turn offers more comfort to standees while standing in super dense crush load condition. Presented discussions in this research are important to policy-makers and planners in the Mumbai Railway Vikas Corporation to monitor, measure and develop programs for the local train operation service quality. The study findings will be useful for developing a policy framework to deal with issues related to the level of service improvement for the suburban rail system in India and other developing economies.

Design a new energy absorber longitudinal member and compare with S-shaped design to enhance the energy absorption capability

A numerical investigation study of both direct and oblique crush loading was implemented. The study used ductile metallic alloy (mild steel A36) and magnesium alloy (AZ31). The study used hexagonal tube as longitudinal members. The current design consists of two parts, the inner tube which is the longitudinal and the outer is the supporting system which is the telescope. Aluminum foam incorporated to the design to enhance the crashworthiness performance. The design is subjected to impact speed of 54 km/h with the impact mass of 1100 kg using three different collision directions: direct, 40 per cent offset and oblique direction with 30 degrees.From the SEA results it can be concluded that the current design (made of steel) enhanced the specific energy absorption by 194% from the highest design used. While the current design made up of magnesium alloy increased the SEA by 255% from the best design which was foam filled s-shaped with square section. The decelerations of the current design for the three directions were at the low permit level which will put the compartment car at the low level of deformation during collision.

Fabrication and characterization of Li4SiO4 pebbles by extrusion spherodization technique: Effects of three different binders

The present report demonstrates the effects of three different binders on fabrication of Li4SiO4 pebbles by extrusion-spherodization technique. It is found that the nature of binders, concentrations and moisture content have significant effect on the density, sphericity, grain size and crush load of the Li4SiO4 pebbles. Different viscosity grade binders namely PVA, PVP and guargum have been explored for the fabrication of pebbles. XRD, FESEM, BET, Inverse gas chromatography, pebble crush load tester are used to study different properties. It has been observed that the pebbles fabricated with 6 wt% PVP show the desired properties [appreciable density (85%), smaller grain size (<8 µm), good sphericity (0.98) and notable crush load (17 N)] when compared with the other two binders. Surface energy and microstructure of the green aggregates provide some comprehensive information for achieving desired properties in PVP derived pebbles. The effects of the sintering temperature on the different properties have also been studied.

Energy absorption analysis for tapered multi-cell tubes improved by foams: Theoretical development and numerical simulation

In this paper, Energy absorption characteristics of tapered multi-cell tubes improved by foams are studied. For the energy absorption process, a theoretical formulation is developed to represent the mean crush load of the foam-filled tubes considering a combination of mean crush loads due to non-filled tube, the foam-filler, and a frictional resistance between them (interaction effects). The formulation is based on the assumptions including equivalent segmented non-tapered single-cell tubes as well as a parallel resisting force of the contributors (non-filled tubes, foam-filler, and interaction effects). Moreover, an extensive numerical analysis on the crushing of the foam-filled tapered multi-cell tubes, with a taper angle ranging from 0 to 7 degrees, a wall thickness ranging from 0.25 to 3 mm, and a cell number ranging from 11 to 10 × 10, is conducted to evaluate the effects of side wall tapering, cross section’s division into multiple cells and wall thickness enlargement on the crashworthiness characteristics. Analyses indicate that there are significant enhancements in the energy absorption behavior of the foam-filled tubes with respect to the non-filled ones. As a special case, the force-displacement results obtained in the numerical simulation are verified against those experimentally observed and reported in the literature for a foam-filled non-tapered single-cell tube.

Crushing behavior and energy absorption performance of a bio-inspired metallic structure: Experimental and numerical study

A thin-walled structure inspired from a biologic creature known as balanus was investigated experimentally and numerically under quasi-static and dynamic loads for load-carrying and energy absorption properties. The structure was composed of an inner conical core with a hemispherical cap and an outer shell in frusto-conical shape and formed by deep drawing. The applied deep drawing process was modelled using nonlinear finite element code LS-DYNA to determine the residual stress/strain and the non-linear thickness distribution after the forming process. It was also shown that the load carried by the balanus structure was greater than the arithmetic sum of the load carried by the inner core and by the outer shell separately. Although the mean force increase due to interaction effect at quasi-static strain rate was approximately 5%, while it increased to roughly 26% at dynamic strain rates in drop weight experiments. The numerical models also showed that the outer shell absorbed more energy than the inner core while the difference between the energy absorbing performance of the core and shell decreased with increasing deformation rate. The effect of strain rate and inertia on the increase in crush load increased with increasing impact velocity, while the strain rate effect had greater influence than the inertia on the crush load. The increased load carrying capacity of the balanus at quasi-static and dynamic strain rates was ascribed to the interaction between the core and shell and the confinement effect of the outer shell particularly at dynamic strain rate.

Fabrication and Characterization of Li&lt;sub&gt;4&lt;/sub&gt;SiO&lt;sub&gt;4&lt;/sub&gt; Ceramic Pebbles Doped with Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3 &lt;/sub&gt;and Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;

Tritium breeder blanket has been considered as one of the most important components of thermonuclear fusion reactor. Recently, Li4SiO4has been regarded as one of the favored ceramics breeders as it exhibits excellent tritium release properties. In order to further improve the comprehensive properties of Li4SiO4pebbles, the grain size and crush load of Li4SiO4pebbles doped with Y2O3and Nb2O5were systematically studied in this work. The results showed that the relative density of Li4SiO4pebbles was increased to 87.2% and the crush load was increased from 43N to 48N when Y2O3doping was used. In view of inhibiting grain growth and increasing the crush load and relative density of Li4SiO4pebbles, the effect of Nb2O5doping was better than that of Y2O3doping.

Study on the Chemical Compatibility Study Between Li2TiO3 Pebbles and 14Cr-ODS Steel

In order to investigate the chemical compatibility between tritium breeder Li2TiO3 pebbles and tritium breeder blanket material oxide dispersion strengthened (ODS) steel, the contact interface between Li2TiO3 pebbles and ODS steel heated in argon atmosphere at 500, 600 and 700 °C for 300 h was studied. It was found that the ions of pebbles could diffuse and corrode with the cladding material after a long-time reaction at high temperature. The corrosion area formed on the surface of Li2TiO3 pebbles was small. With the increase of temperature, a zone with enriched iron was found on the surface of the pebble. This part of the surface was the direct contact surface between the pebble and the steel. At the same time, the relative density of the pebbles increased and the crush load was decreased to 30 N. In addition, a slight corrosion phenomenon was found on the surface of ODS steel. It has been proved that the main components of the corrosion products were the complex oxide containing Fe and Cr and the complex oxide containing Li and Fe.

Fabrication and characterization of Li4SiO4-Li2TiO3 composite ceramic pebbles using extrusion and spherodization technique

The effect of different amount of Li2TiO3(LT) (0–15 wt%) addition on the properties of composite Li4SiO4 (LS) ceramic pebbles were studied. The Li4SiO4-Li2TiO3 composite powder was prepared in-situ using solid state method at a calcination temperature as low as 800 °C. The composite pebbles were fabricated using a cost-effective and simple technique called extrusion-spherodization. The sintered pebbles were characterized for density, grain size, pore size distribution, crush load and moisture stability. The density of Li4SiO4 composite pebbles was improved for LS-5 wt% LT in comparison to LS pebbles when fired at 1000 °C. Moreover, the LS grain size in the composite pebbles was reduced (5.8 μm) in comparison to LS pebbles. We also found that the average crush load value of the LS-5 wt%LT composite pebbles had been improved by nearly 100% (33 N) to that of the pure LS pebbles (17 N). The LS-5 wt% LT pebbles showed improvement in stability to moisture.

Crush simulation of automotive chopped fiber composite structures by de-homogenization multi-scale computational method

A de-homogenization multi-scale computational method is proposed for the virtual performance simulation of chopped fibers composites under crush loadings. The novel approach led to the development of a multi-scale material characterization procedure for composite systems, comprising of: (1) chopped fibers homogenization based on the Eshelby and Mori–Tanaka inclusion theories, (2) orientation tensor stiffness averaging technique, (3) micro- and macro-mechanics damage and failure theories, and (4) crush resistance evaluation, as a part of the durability and damage tolerance analysis. The chopped fibers material model developed in this work is then employed in a finite element analysis, interfaced with a multi-scale progressive failure technique to track damage and fracture evolution. Comparison of the simulation results obtained for two tubes, manufactured by injection and compression molding respectively, shows good agreement with the crush test data within 10% accuracy. The proposed de-homogenization method offers a superior load resistance prediction over commercially available techniques. Furthermore, the implementation of the proposed approach in our in-house software provides traceable damage evolution and visualization of the contributing failure mechanisms, valuable sources for the design and development of new composite structures.

Fabrication of Li2TiO3 ceramic pebbles with fine microstructure by microwave sintering

Lithium metatitanate (Li2TiO3) ceramic pebbles were successfully fabricated by microwave sintering using the powders synthesized via solid state reaction. Nano-size Li2TiO3 powders with an average particle size of 45 nm were synthesized by solid state reaction, and wet process was employed to fabricate Li2TiO3 pebbles with good sphericity. The pebbles were sintered by microwave process with rapid heating rate. Due to the volumetric heating and enhanced diffusion of microwave sintering, the sintered Li2TiO3 ceramic pebbles show high density (>85%T.D.), high crush load and uniform microstructure with small grain size (100 nm–1 μm), which might hold good potential in tritium release and long-term stability. The results show that the microwave sintering is a promising process for the fabrication of Li2TiO3 pebbles with fine microstructure and good mechanical property.

Energy absorption study considering crush test on carbon fiber/epoxy and carbon fiber/polyurethane structural composite beams

Crashworthiness of a high-performance composite structure is associated to its energy absorption capacity through controlled failure mechanisms during an impact or crushing event. Furthermore, crush and compression testing usually characterize the failure mechanisms, which considers the specimen geometry, material type, fiber architecture and loading rate. This study focuses on energy absorption capability of carbon fiber/epoxy (CF/Epoxy) and carbon fiber/polyurethane (CF/PU) composite hat beams (HB) by a nonstandard quasi-static crush test for crashworthiness applications, including a discussion of how the material properties affect the structural behavior. In addition, the materials evaluation by low velocity impact (LVI), compression after impact (CAI) test, and in-plane shear response by tensile test was performed to determine and compare mechanical behavior and damage modes caused by the impact event. Despite the differences observed on the CF/Epoxy and CF/PU composites in terms of energy absorption capacity on impact, post-impact compression strength and shear strength, the HB specimens presented similar average crush force when subjected to the crush loading, but different types of failure modes. A multiple linear regression model has been developed which is able to predict the HB absorbed energy on crush considering the matrix behavior and energy absorption capability corresponding the failure mechanisms observed.

High temperature oedometric compression of Li2TiO3 pebble beds for Indian TBM

Lithium Metatitanate (Li2TiO3 or LMT) and Lithium Orthiosilicate (Li4SiO4 or LOS) are the prominent among the suitable candidate materials for breeders. Robust design of the breeder blankets requires a thorough understanding of the thermo-mechanical response of the breeder materials at different loading conditions. In this context, the material characterization plays a vital role. Solid breeder concept of various member nations comprises of pebbles in steel container. Determination of effective properties of the pebble beds helps in understanding and formulation of constitutive relations for such granular systems. In order to develop simulation tools to understand the complex thermo-mechanical response of the breeder units, the properties of the material should be known. Hence, the objective of this work is to characterize crush load of Li2TiO3 pebbles and investigate the thermo-mechanical response of the pebble beds. The study involves determining the crush load of individual pebbles and pebble-bed elastic modulus. Uniaxial oedometric tests are performed to investigate the influence of temperature on the effective elastic modulus of the pebble beds.

Microstructure and phase evolution of Li4TiO4 ceramics pebbles prepared from a nanostructured precursor powder synthesized by hydrothermal method

Li4TiO4 ceramics pebbles have been proposed to be a promising tritium breeder materials for the fusion reactor blanket of the International Thermonuclear Experimental Reactor (ITER). In the present study, the hydrothermal method was first used to synthesize the nanostructured precursor powders for fabricating the Li4TiO4 ceramic pebbles. The precursor powders were composed of LiOH, Li2CO3 and Li2TiO3 with a grain size of 30–80 nm. Moreover, the microstructure and phase evolution of Li4TiO4 ceramics pebbles were investigated. The results indicated that the formation temperature of Li4TiO4 by hydrothermal method was lower than that of other methods. The pure phase Li4TiO4 ceramic pebbles with small grain size (average value 0.50 μm), satisfactory crush load (average value 41 N) and reasonable pore structure was sintered at 750 °C for 4 h in vacuum. This study provides a new method for preparing a high quality Li4TiO4 ceramic pebble, which has potential application as a tritium breeding material.