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The purpose of this paper is to introduce a computational time dependent modeling to investigate propagation of elastic-viscoplastic zones in the shock wave loaded circular plates.

Constitutive equations are implemented incrementally by the Von-Kármán finite deflection system which is coupled with a mixed strain hardening rule and physical-base viscoplastic models. Time integrations of the equations are done by the return mapping technique through the cutting-plane algorithm. An integrated solution is established by pseudo-spectral collocation methodology. The Chebyshev basis functions are utilized to evaluate the coefficients of displacement fields. Temporal terms are discretized by the Houbolt marching method. Spatial linearizations are accomplished by the quadratic extrapolation technique.

Results of the center point deflections, effective plastic strain and stress (dynamic flow stress) and temperature rise are compared for three features of the Von-Kármán system. Identifying time history of resultant stresses, propagations of the viscoplastic plastic zones are illustrated for two circumstances; with considering strain rate and hardening effects, and without them. Some of modeling and computation aspects are discussed, carefully. When the results are compared with experimental data of shock wave loadings and finite element simulations, good agreements between them are observed.

This computational approach makes coupling the structural equations with the physical descriptions of the high rate deformation through step-by-step spectral solution of the constitutive equations.

Under dynamic loading shock waves propagate in metallic materials and may be concentrated after reflection from fixed boundaries. In these cases high strain rate gradients are initiated in the material, which are accompanied by a change in temperature due to the adiabatic character of high rate deformation processes. In order to estimate the mechanical behaviour of the material under multiaxial dynamic loading constitutive equations must be worked out, which have to be valid over wide ranges of strain rate and temperature. Often a viscoplastic behaviour is assumed using the equation of Perzyna:

This paper aims to study frictional characteristics of thin-walled tubes in the liquid impact forming (LIF) process.

LIF experiments under various impacting velocities were performed on SUS304 stainless steel tubes with various guiding lengths on a custom-designed measurement system to investigate the effects of impacting velocity and guiding length on the coefficient of friction (COF) in the guiding zone.

The results indicate that the COF changes dynamically in the guiding zone and decreases with the deformation process. The reduction range of the COF is wider in LIF than in both the conventional and pulsating hydroforming (THF), which may be contributed to the impacting velocities in a short time. Moreover, the COF decreases faster in the first half of the LIF process than in the second half. Under different impacting velocities and guiding lengths, the decreasing rate of the COF in the first half is more sensitive and obvious than that in the second half.

A method for determining the COF in the guiding zone in LIF is proposed and the frictional characteristics in LIF are studied. Comparing the COF of tubes in conventional THF, pulsating THF and the LIF process is valuable for improving and predicting the tubular formability in various hydraulic environments for industrial production.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0269

The purpose of this paper is to present a finite element simulation to validate the strength and energy absorption capacity of a rollover protective structure (ROPS) of agricultural tractors. The test consists of four steps: rear loading, crushing of the rear columns, side loading and crushing of the front columns. In this study a new design of a cabin for narrow tractors was simulated and from it the computational test was run for validation of the cabin. The simulation was performed using ANSYS software, considering the nonlinear characteristics of the materials, since during the test the plastic limit is reached. With the computational results, it was possible to predict the behavior of the structure before the real test. These results were used to propose design and materials changes that significantly improved the energy absorption, making it more efficient. The proposed cabin design reaches the energies and forces required in each step of the computational simulation of the ROPS test and the deformation needed to achieve them does not cause any cabin part to enter the operator survival space inside the cabin.

In the present study, numerous finite elements simulations have been carried out on a narrow cab for tractors.

It was conclude that it is possible to virtually test the ROPS, making material and design changes in order to have a more adequate structure before a first real test.

The present study is part of Tiago R. Cesa's Master thesis, an original research work.

The purpose of this paper is to identify the energy absorption characteristics of arch micro-strut (ARCH) lattice structure (different from traditional straight micro-strut lattice structure) under high-speed impact, and promote the development of special-shaped micro-strut lattice structure.

The study serves to study the anti-impact and energy absorption characteristics of ARCH lattice structure under different strain rates and different unit layers of lattice structure. In this paper, quasi-static compression and Hopkinson compression bar experiments are used for comparative analysis.

The results show that the ARCH lattice structure has obvious strain rate effect. When the strain rate is low, the number of layers of lattice structure has a great influence on the mechanical properties. With the increase of strain rate, the influence of the number of layers on the mechanical properties gradually weakens. So the ARCH lattice structure with fewer layers (less than five layers) should be selected as the impact energy absorbing materials at lower impact rate, while at higher impact rate, the number of layers can be selected according to the actual requirements of components or devices space size.

This study shows that Arch lattice structure has excellent energy absorption performance, and provides a theoretical reference for the application of ARCH lattice structure in energy-absorbing materials. ARCH lattice structure is expected to be applied to a variety of energy absorption and anti-impact components or devices, such as aircraft black box fall buffer components, impact resistant layer of bulletproof and landing buffer device.

An overview of the mechanical behaviour of common solder types is presented, with particular emphasis placed upon those properties relevant to the performance of soldered joints in service. The requirements for more sophisticated and complex information are highlighted in order to assist design for the increasingly arduous demands associated with miniaturisation.

The purpose of the study was to investigate the spalling phenomenon in ultra-high performance fibre reinforced concrete (UHPFRC) beams on exposure to a standard fire curve (ISO 834) under a sustained load.

The variables in this study were steel fibre dosage, polypropylene (PP) fibres and loading levels. The research investigated seven beams – three of which contained steel fibres with 2 vol.%, another three had steel fibres with 4 vol.% dosage and the seventh beam had a combination of steel fibres (2 vol.%) and PP fibres (4 kg/m³). The beams were tested for 1 h under three loading levels (20, 40 and 60 per cent) based on the ambient temperature ultimate flexural strength of the beam.

Spalling was affected by the loading levels; it exacerbated under the load level of 40 per cent, whereas under the 60 per cent load level, significantly less spalling was recorded. Under similar loading conditions, the beams containing steel fibres with a dosage of 4 vol.% spalled less than the beams with fibre contents of 2 vol.%. This was attributed to the additional tensile strength provided by the excess steel fibres. The presence of PP fibres eliminated spalling completely.

There is insufficient research into the performance of UHPFRC beams at elevated temperature, as most studies have largely focussed on columns, slabs and smaller elements such as cubes and cylinders. This study provides invaluable information and insights of the influence of parameters such as steel fibre dosage, PP fibres, loading levels on the spalling behaviour and fire endurance of UHPFRC beams.

In this study, waste iron scale, which occurs in high amounts during steel production and contains high amounts of iron element, was used as a reinforcing material in the polypropylene (PP) matrix.

In the PP matrix, 33 micron-sized iron scale was added at 5%, 10%, 15% and 20% ratios. The composites were subjected to mechanical and dry sliding wear tests. The wear mechanisms occurring on the wear surfaces were determined by SEM supported by EDS. Tensile testing was performed using a tensile tester. Hardness tests were performed using a Shore-D hardness tester with ASTM-D-22 standards.

Composite reinforced with 5% iron scale showed the highest tensile strength. The addition of higher amounts of iron scale particles reduced the tensile strength of the composites compared to PP. Hardness increased from 58 to 64 Shore-D with the increase in scale content. The reinforcement of PP with iron scale increased the dry sliding wear resistance.

According to the authors’ knowledge, in the literature review, there was no study found on the effect of iron scale reinforcement on PP.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2020-0316/

The purpose of this paper is to compare the influence of relative density (RD) and strain rates on failure mechanism and specific energy absorption (SEA) of polyamide lattices ranging from bending to stretch-dominated structures using selective laser sintering (SLS).

Three bending and two stretch-dominated unit cells were selected based on the Maxwell stability criterion. Lattices were designed with three RD and fabricated by SLS technique using PA12 material. Quasi-static compression tests with three strain rates were carried out using Taguchi's L9 experiments. The lattice compressive behaviour was verified with the Gibson–Ashby analytical model.

It has been observed that RD and strain rates played a vital role in lattice compressive properties by controlling failure mechanisms, resulting in distinct post-yielding responses as fluctuating and stable hardening in the plateau region. Analysis of variance (ANOVA) displayed the significant impact of RD and emphasised dissimilar influences of strain rate that vary to cell topology. Bending-dominated lattices showed better compressive properties than stretch-dominated lattices. The interesting observation is that stretch-dominated lattices with over-stiff topology exhibited less compressive properties contrary to the Maxwell stability criterion, whereas strain rate has less influence on the SEA of face-centered and body-centered cubic unit cells with vertical and horizontal struts (FBCCXYZ).

This comparative study is expected to provide new prospects for designing end-user parts that undergo various impact conditions like automotive bumpers and evolving techniques like hybrid and functionally graded lattices.

To the best of the authors' knowledge, this is the first work that relates the strain rate with compressive properties and also highlights the lattice behaviour transformation from ductile to brittle while the increase of RD and strain rate analytically using the Gibson–Ashby analytical model.

The prime task of research in hot forging industry is to improve the service life of forging dies. The in-service microstructural changes that may occur in a die during hot forging is expected to significantly affect the service life. The purpose of this work is to analyse the microstructural evolution of double tempered hot forging dies in a real industrial environment, and the correlation of microstructural and microhardness evolution to the in-service wear and plastic deformation.

Specific hot forging tests were carried out on double tempered AISI H11 chromium tool steel for 100, 500 and 1,000 forging strokes. Macro analysis was conducted on die cross section to analyse the wear and plastic deformation at different stages of forging cycles. Microhardness and microstructural analyses were performed on the die surface after these forging tests.

The macro analysis on the transverse section of dies shows that wear is predominant during initial forging strokes, whereas plastic deformation is observed in later stages. Microstructural analyses demonstrate that during first 500 forging cycles, carbide population decreases at 63 per cent higher rate as compared to corresponding drop during 501 to 1,000 forging cycles. Additionally, the carbide size increases at all stages of forging cycle. Further, microstructural images from dies after 1,000 forging strokes show clustering and spherodisation of carbides by which the “blocky”-shaped carbides in pre-forging samples had spherodised to form “elongated spherical” structures.

The findings of this work can be used in hot forging industries to predict amount of wear and plastic deformation at different stages of service. From the results of this work, the service life of double tempered H11 hot forging dies used in forging without lubrication is within 501 to 1,000 forgings.

Most of the literatures are focussed on the cyclic softening of material at constant temperature. This work analyses the microstructural evolution of double tempered hot forging dies in a real industrial environment and correlates the microstructural and microhardness evolution to the in-service wear and plastic deformation.