The effect of crack insertion for FDM printed PLA materials on Mode I and Mode II fracture toughness

The paper presents mode I and II fracture toughness results for polylactic acid material obtained via fused deposition modeling. The tests were performed using Single Edge Notch Bend specimens loaded in four point bending: symmetric for mode I, asymmetric for mode II, respectively. The notch was inserted by 3D printing, and by milling, respectively. Fracture toughness values measured for the specimens with 3D printed notch resulted to be higher than those obtained by milling. The effect of notch insertion is more evident in mode I while it is less important for mode II

The notch effect on fracture of polyurethane materials

This paper investigates the fracture properties and notch effect of PUR materials with four different densities. The asymmetric semi-circular bend specimen was adapted to perform mixed mode fracture toughness tests. This semi-circular specimen with radius R, which contains an edge crack of length a oriented normal to the specimen edge, loaded with a three point bending fixture, was proved to give wide range of mixed modes from pure mode I to pure mode II, only by changing the position of one support. Different types of notched specimens were considered for notch effect investigations and the Theory of Critical Distances was applied. It could be seen that the critical distances are influenced by the cellular structure of investigated materials

Scaling of compression strength in disordered solids: metallic foams

The scaling of compression strength with porosity for aluminium foams was investigated. The Al 99.96, AlMg1Si0.6 and AlSi11Mg0.6 foams of various porosity, sample size with and without surface skin were tested in compression. It was observed that the compression strength of aluminium foams scales near the percolation threshold with Tf ? 1.9 - 2.0 almost independently on the matrix alloy, sample size and presence of surface skin. The difference of the obtained values of Tf to the theoretical estimate of Tf = 2.64 ± 0.3 by Arbabi and Sahimi and to Ashby estimate of 1.5 was explained using an analogy with the Daoud and Coniglio approach to the scaling of the free energy of sol-gel transition. It leads to the finding that, there are two different universality classes for the critical exponent Tf: when the stretching forces dominate Tf = f = 2.1, respectively when bending forces prevail Tf = ?.d = 2.64 seems to be valid. Another possibility is the validity of relation Tf ? f which varies only according to the universality class of modulus of elasticity in foam

On the crack path under mixed mode loading on PUR foams

 In this paper are presented the crack initiation angles obtained in polyurethane (PUR) foams under mixedmode loading. Closed cell rigid PUR foams having three different densities 100, 145, and 300 kg/m3 were investigated.Experiments were performed using Asymmetric Semi-Circular Bend and Single Edge Crack specimens.The obtained crack initiation values were compared with four fracture criteria to introduce: Maximum Tensile Stress, Strain Energy Density, Maximum Energy Release Rate and Equivalent Stress Intensity Factor, and a good agreement was observed. This allow to conclude that the theoretical fracture criteria developed for solid material could be used with success to predict the crack propagation angles in cellular materials like PUR foams.&nbsp

An engineering approach to predict mixed mode fracture of PUR foams based on ASED and micromechanical modelling

The Averaged Strain Energy Density (ASED) criteria is applied herein to reinterpret the fracture data of PUR foams. Four type of specimens were used in fracture tests. The ASED parameters were determined based on micromechanical models. The volume control for cracked components is represented by a circle with the centre at the crack tip for all type of fracture modes. It was also demonstrated that the SED parameters obtained from pure mode I could be applied successfully for mixed modes and mode II. This approach represents an useful engineering tool for the assessment of brittle fracture of components made of cellular materials

Metal Foam-Filled Tubes as Plastic Dissipaters in Earthquake-Resistant Steel Buildings

The aim of this paper is to investigate whether metal-foam-made devices can be effective to dissipate seismic energy in buildings during strong earthquakes. To this purpose, non-linear numerical analyses of concentrically braced steel buildings under recorded ground motions have been carried out, while some experimental tests on metal-foam specimens and metal-foam-filled tubes have been performed. Foam-based devices are assumed to be inserted within the diagonal braces of the considered steel frame to dissipate energy by plastic deformation during strong earthquakes. To apply the experimental data, a scaled numerical model of the prototype building has been implemented by means of the similitude theory and the Buckingham Π theorem. The results of the study provide a preliminary assessment of the potential of metal foam-based dissipaters to reduce the seismic effects in civil structures