Papers by Keyword: Material Characterisation

Abstract: In the last years, the induced seismicity in the northern part of the Netherlands has considerably increased. The existing building stock was not designed for seismic loading, and it is characterised by very slender walls, limited cooperation between walls and floors, and use of cavity walls. As a consequence, the validation of analytical and numerical models for the assessment of unreinforced masonry buildings and the characterisation of the masonry at both material and structural level have become of great importance. An extensive large-scale testing program was performed at the Delft University of Technology in 2015 to create benchmarks for the validation of the numerical and analytical models. The attention was mainly devoted to a terraced house typology, which was widely adopted for housing in the period 1960-1980, and focused on the characterisation of the typology at various levels: material, connection, component and assemblage level. The experimental tests at component and assemblage levels were also reproduced by nonlinear finite element analysis, validated and calibrated against the data available from the testing campaign at material level. In this paper, an overview description of performed experiments and numerical analyses is provided; specific devotion is given to the main outcomes of the campaign and to the lessons learned by the experimental evidences for improving the numerical models.

Abstract: High performance rockets are developed using cryogenic technology. High thrust cryogenic rocket engines operating at elevated temperatures and pressures are the backbone of such rockets. The thrust chamber of such engines, which produce the thrust for the propulsion of the rocket, can be considered as structural elements. Often double walled construction is employed for these chambers for better cooling and enhanced performance. The thrust chamber investigated here has its hot inner wall fabricated out of a high conductivity high ductility copper alloy and outer wall made of a ductile stainless steel. The engine is indigenously designed and developed by ISRO and is undergoing hot tests. Inner wall is subjected to high thermal and pressure loads during operation of engine due to which it will be in the plastic regime. Evaluation of tensile properties of the copper alloy and stainless steel up to fracture, at cryogenic, ambient and elevated temperatures in parent metal and welded forms is of paramount importance for its constitutive modelling and thermo structural analysis of the thrust chamber.

Abstract: Multi-material and hybrid constructions are increasingly used in the automotive industry with the aim of achieving significant weight reductions of conventional car bodies, and thereby lead to effective reductions of fuel consumption. In this respect, the use of aluminum and short fiber reinforced plastics represents an interesting material combination. A full exploitation of such a material combination requires a suitable joining technique. Among different joining techniques, clinching represents one of the most appealing alternatives for automotive applications. This contribution deals with the experimental tests for determination of material behaviour of two representative materials PA6GF30 and EN AW 5754, which are used for parameterization of material models needed for numerical analysis of the clinching process using the FE software LS-DYNA. With regard to the material modeling of the aluminum sheet, an isotropic material model based on the von Mises plasticity implemented in LS-DYNA was chosen. For the description of the strain hardening behaviour of the aluminum sheet at high equivalent plastic strains, the hydraulic bulge test was carried out in addition to the uniaxial tensile test. For modeling of the short fiber reinforced thermoplastic a semi-analytical model for polymers (SAMP-1) available in LS-DYNA was taken. This material model uses an isotropic pressure dependent yield surface for the description of homogeneous materials. Finally, the FE model of clinching process is presented and an outlook of planned activities is given in terms on determination of the yield surface and hardening behaviour of PA6GF30 at high plastic strains.

Abstract: Aluminium cast products are becoming more and more interesting for energy absorbing applications, as a higher functional integration can be achieved with casting processes. Therefore, it is required to find a way to characterise different aluminium alloys regarding their energy absorption behaviour. Energy absorption phenomena in materials depend on the combination of material and geometry on a macro scale level. One of the main contributions of the current research work is to show that the full realization of material absorbing capacity may not be achieved by more complex geometries. Consequently, for the characterisation of cast material under crash load, it is very important to keep the geometry influence on the energy absorption behaviour as low as possible. The ultimate aim herein is to determine an optimised geometry setup to characterise different aluminium casting materials. Three different test geometries were chosen for numerical investigations. All specimens possess the same cross-sectional area and also the same second moment of inertia. The specimens have been tested under an axial crash load at constant speed. Failure has been simulated using a Johnson-Cook damage and failure model. Their absorbing behaviours will be compared and based on the existing literature a theoretical discussion about the geometrical influence will also be given.

Abstract: The analysis of deformation and damage behavior of aluminum cast components is very complex, since local mechanical properties in the components are inhomogeneous as a consequence of spatial distribution of microstructure e.g. pore size, grain size and arm spacing of secondary dendrites. Moreover, the damage behavior of aluminum alloys depends strongly on stress state. Until now it is not clear how the pore morphology affects the damage behavior under different loading situations. In this work the damage behavior of the aluminum die casting alloy AlSi9Mn was characterized with tension specimens extracted from different positions in a component. Damage effect was modeled with representative volume elements (RVE) with variation of porosity, pore size and distribution of pores under uniaxial and biaxial tension, plane strain, compression and shear. Not only pore growth and coalescence but also damage of the matrix material was taken into account in the simulations. A large influence of pore morphology on fracture strain was found and relationships between fracture strain and pore morphology were proposed for different stress states.

Abstract: There is a need to search for efficient material that reduce CO₂ content and enhance the hydrogen composition in the product gas from biomass steam gasification particularly for large scale production. The present study was carried out to perform the characterization of commercial quicklime as CO₂ absorbent and Ni powder as catalyst. The chemical composition of the materials perform using x-ray fluorescence (XRF) indicated high amount of CaO and Ni in the bulk samples. Using XRF and SEM analyses, it was found that both materials showed high crystalinity. The adsorption isotherm from physisorption analysis suggested that the materials exhibits Type II category according to the IUPAC classification scheme. These types of material exhibit mesoporous structure which was also verified by the pore size of the samples found via BET analysis. The BET surface area reported was 4.16 m²/g and 0.78 m²/g for quicklime and Ni powder, respectively. In conclusion, commercial quicklime has the potential as CO₂ absorbent, based on the pore size and surface area. Conversely, the surface properties of the Ni powder were found relatively lower as compared to other commercial catalysts available for biomass steam gasification.

Abstract: There is a need to search for efficient material that reduce CO₂ content and enhance the hydrogen composition in the product gas from biomass steam gasification particularly for large scale production. The present study was carried out to perform the characterization of commercial quicklime as CO₂ absorbent and Ni powder as catalyst. The chemical composition of the materials perform using x-ray fluorescence (XRF) indicated high amount of CaO and Ni in the bulk samples. Using XRF and SEM analyses, it was found that both materials showed high crystalinity. The adsorption isotherm from physisorption analysis suggested that the materials exhibits Type II category according to the IUPAC classification scheme. These types of material exhibit mesoporous structure which was also verified by the pore size of the samples found via BET analysis. The BET surface area reported was 4.16 m²/g and 0.78 m²/g for quicklime and Ni powder, respectively. In conclusion, commercial quicklime has the potential as CO₂ absorbent, based on the pore size and surface area. Conversely, the surface properties of the Ni powder were found relatively lower as compared to other commercial catalysts available for biomass steam gasification.

Abstract: In several fields of engineering the automation of the CFRP production chain is a major issue. In this production chain the forming plays a key role, as the result of the forming influences everything in the chain from the infusion step until the part mechanics. To understand the influence of the material choice onto the forming process is a task followed by many scientists during the last 20 years. Basic tests for shear characterization like Picture Frame Test (PFT) and Bias Extension Test (BiasExt) were developed and used widely. This work deals with the comparison of the BiasExt to a fiber extraction test. The fiber extraction test is developed and used for the characterization of a woven and two non-crimp fabric material. The results are important for the process information and the judgment of primary deformation mechanisms. The tests are simulated for the unidirectional material in a mesoscopic approach and the results are compared in order to judge the capability of the mesoscopic simulation and its residual limitations.

Abstract: Recent studies showed that electrical conductivity is a valuable technique to identify the different zones of solid-state welded joints with a good correlation with the microstructure and hardness. This is a relevant result since this technique is expedite and, in some cases, non destructive. The concept was applied to other welding processes as the ones involving fusion and to a wide range of materials. For this, a comprehensive study was performed using friction stir welding, tungsten inert gas (TIG) and gas metal arc (MAG) welding processes in either bead on plate or butt joints in: carbon steel, magnesium and titanium. Eddy current non-destructive testing (NDT) was used to measure the electrical conductivity at different depths in transverse sections of the processed materials. The obtained profiles were compared to the hardness profiles in the same sections. As a result, a good correlation was observed in most materials welded by solid state and by fusion processes. The variation of the electrical conductivity closely follows the one detected in the hardness. Another interesting conclusion is that, even for fusion welding of carbon steels, the technique has potential to complement the hardness measurements and microstructural observations, allowing to identify the distinct zones of welds in materials commonly used in industry.

Abstract: Presently, the need to characterize the constitutive parameters of materials has increased due to the manufacture of new materials and development of computational analysis software intending to reproduce the real behavior which depends on the quality of the models implemented and their material parameters. However, in order to identify all constitutive parameters of materials a large number of mechanical tests is required. Thus, only one mechanical test that could allow to characterize all the mechanical properties could be desired. Hence, the aim of this work is to propose a methodology that find the most informative loading path in the sense of display normal and shear strains as clear aspossible to warrantee that the solution is the most unique and distinguishable for the parameter identification process. To achieve this objective the proposed methodology uses Finite Element Analysis (FEA) and Singular Value Decomposition (SVD) coupled together with optimization strategies. Thismethodology is presented for elastoplasticity behavior.