Tomasz Sadowski

Estimation of the crack length after thermal shock in FGM strip

Thermal shock in a strip with a functionally graded Al2O3/Al interpenetrating network microstructure is modelled. The problem of thermal shock induced crack propagation is analyzed. A strong influence of residual stresses and the type of composition gradient on the crack length is predicted. The type of property gradient required in order to achieve an optimal thermal shock resistance is discussed.

Assessing the Influence of Porosity in the Deformation of Metal–Ceramic Composites

The aim of the paper is to develop the previously formulated model [19, 20] of the polycrystalline composite to include porosity growth at metallic interfaces of metal–ceramic composites (MCCs). Examples of this kind of MCCs are: (1) a two-phase material composed of brittle grains WC joined by the plastic binder Co, which can contain a small degree of porosity introduced during the cooling process [31], (2) TiC–Mo2C hard phase grains surrounded by tough binder phase Ni [12]. This work focuses on the description of the deformation of the MCC material including the modelling of a real material internal structure taking into account porosity growth during the loading. Experimental observations of the WC/Co composite [10] indicate that the majority of the fracture energy of MCC is expended through ductile failure of the plastic binder Co (dimple rupture across the binder or in the binder near the binder/carbide interface). This process is preceded by porosity growth at metallic interfaces and finally leads to inter-granular cracks propagation. This paper presents micromechanical modelling of the MCC response in the case of uniaxial tension of 3-D Representative Volume Element (RVE) with the application of the Finite Element Analysis (FEA). The MCC material includes: elastic grains and inter-granular metallic layers containing technological pores that create its real complex internal structure. The quasi-static deformation process of the material comprises elastic deformation of brittle grains, elasto-plastic deformation of inter-granular layers (of different thickness: 2–4 μm) and additional deformation due to micro-porosity development in the layers. A micro-sample analysis leads to the conclusion that a small amount of technological porosity changes the qualitative behaviour of the MCC including deformation, rotation of grains, roughness, and level of plastic strains.

Study of factors influencing the mechanical properties of polyurethane foams under dynamic compression

Effect of density, loading rate, material orientation and temperature on dynamic compression behavior of rigid polyurethane foams are investigated in this paper. These parameters have a very important role, taking into account that foams are used as packing materials or dampers which require high energy impact absorption. The experimental study was carried out on closed-cell rigid polyurethane (PUR) foam specimens of different densities (100, 160 respectively 300 kg/m 3 ), having a cubic shape. The specimens were subjected to uniaxial dynamic compression with loading rate in range of 1.37-3.25 m/s, using four different temperatures (20, 60, 90, 110°C) and two loading planes (direction (3) - rise direction and direction (2) - in plane). Experimental results show that Youngs modulus, yield stress and plateau stress values increases with increasing density. One of the most significant effects of mechanical properties in dynamic compression of rigid PUR foams is the density, but also the loading speed, material orientation and temperature influences the behavior in compression

Energy - absorption and efficiency diagrams of rigid PUR foams

Polyurethane (PUR) foam materials represent a class of materials widely used for impact protection and energy absorption. This paper presents a characterization of different rigid PUR foams under compressive impact loading by means of energy absorption and efficiency diagrams. Compressive properties were investigated on cubic specimens on the foams’ rise direction at room temperature with a loading rate of 3.09 m/s for three different closed-cell foams with densities of 100 kg/m3, 160 kg/m3 and 300 kg/m3 respectively. Experimental results show that the compression modulus, yield stress and plateau stress increase with density. Most of the energy is absorbed in the plateau region because of the cell deformation associated with this phenomenon, allowing greater absorption of impact energy at nearly constant load. Authors have found that both the energy absorption and efficiency diagrams are consistent and present similar results for studied foams.

Computational Models of Laminated Glass Plate under Transverse Static Loading

Laminated glass with Polyvinyl Butyral (PVB) interlayer became a popular safety glass for aircraft windows, architectural and automotive glazing applications. The very soft interlayer, bonding the glass plates, however, has negligible normal stress in transverse loading and it resists mainly by shear stress. The classical laminate theory obeying the principle of the straight normals remaining straight is not valid for laminated glass. Conventional Finite Elements (FE) are used to model the laminated glass in cylindrical bending to investigate the problem. Based on the assumption that the glass layers of a laminated glass plate obey Kirchoff’s classical plate theory and the PVB-interlayer transfer load by shear stress only, the differential equations of a Triplex Laminated Glass (TLG) plate are derived and a special TLG plate FE is elaborated. For each of its nodes, the element has one transverse translational, three rotational, and two additional degrees of freedom representing the slippage between the glass layers. All computational models are compared with experimental tests of a laminated glass strip in cylindrical bending.

Non-Symmetric Thermal Shock In Ceramic Matrix Composite (Cmc) Materials

A methodology has been proposed to describe CMC and functionally graded materials (FGM) thermomechanical response subjected to sudden changes of the temperature field. Appropriate gradation of the composite properties can significantly improve thermal shock response of the material itself or a structural element. The governing equations for the temperature field under transient thermal loading are formulated, and solution of the analytical and two numerical methods FEA and FD were discussed. The role of the thermal residual stress is significant in the analysis of thermal shock problems. In a non-symmetrical gradation profile they create initial curvature of the FGM structural element. The basic fracture mechanics idea is presented and is applied to CMC and FGM which were subjected to a transient temperature field. In particular the crackbridging mechanism plays an important role in the assessment of the composites response. Numerical examples dealing with 1-D and 2-D non-symmetric thermal shock problem illustrate the effectiveness of the theoretical methods to the solution of practical problems.

Failure of Polyurethane Foams under Different Loading Conditions

Polyurethane foam materials are widely used as cores in sandwich composites, for packing and cushioning. This paper presents the experimental results obtained for the mechanical properties of polyurethane foams in different loading conditions and the influence of impregnation on the mechanical properties. A 200 kg/m3 density polyurethane foam was tested in tension, compression and three point bending. The experimental results show that the impregnation layer has no effect on the strength of the foam, but has considerable influence on the tensile and flexure modulus.

Spot Welding–Adhesive Joints: Modelling and Testing

Modelling and testing of hybrid joints obtained by combination of two simple techniques, i.e., by application of spot welding and adhesive, is reported. The joints were subjected to uniaxial tension. The experiments were performed for: 1) a pure joining of the parts by spot welding and 2) spot welding–adhesive joining of the structural elements. A new experimental method was elaborated with application of two digital image correlation (DIC) systems. The method allowed for online monitoring of the deformation process of the joined elements with complex shapes. Modelling of the hybrid joints response to mechanical loading was performed by ABAQUS code. Damage process in the adhesive layer was taken into account. The obtained results lead to the conclusion that the strengthening of joints by the application of adhesive significantly improves static strength and energy absorption. The visible degradation process of the adhesive layer which started prior to the maximum value of force carrying the hybrid joint was obtained.

Experimental Investigation and Numerical Modeling Fracture Processes under Mode II in Concrete Composites Containing Fly-Ash Additive at early Age

Mode II fracture analysis is especially important. This mode is vital in relation to concrete, due to its relatively low shearing strength and high sensitivity to such type of stress. Nowadays, the structural concretes containing an additives of fly-ash are quite commonly used in the construction industry. Initial cracks origin and development research was carried out using samples for three concrete mixtures: concrete without silica fly-ash (FA), concrete with 20% and concrete with 30% FA additive. 150x150x150 concrete cube with two initial cracks was used as a test sample. Experimental investigation under Mode II fracture was carried out in concrete composites at early age (after 3, 7, 14 and 21 days). X-FEM method enables observation of defect initiation and development, there is no need to input the original conditions. Calculations used peak principal stress criterion. Most calculations coincide with results of experimental research. There was a convergence of: cracks shapes, FQ critical force values, force - displacement graphs.

Macroscopic Evaluation of Fracture Processes in Fly Ash Concrete

This paper presents the results of Mode I fracture toughness tests of concrete with fly ash (FA) loaded in Mode I. Concrete composites with the addition of 0%, 20% and 30% siliceous FA were analysed. Fracture toughness tests were performed on a MTS 810 testing machine. The studies examined the effect of FA additive on the quasi-static fracture toughness KIcS. The analysis of the results revealed that a 20% FA additive causes an increase of KIcS value, while a 30% FA additive causes a decrease on fracture toughness. Additionally, the results demonstrate the possibilities of practical application of ARAMIS system for analysing the development of defects in the micro-structure of concretes containing FA additives. This system can be useful for macroscopic estimation of crack propagation.