Computed Tomography analysis of damage in composites subjected to impact loading

The composites, used in the transportation engineering, include different classes with a wide range of materials and properties within each type. The following different typologies of composites have been investigated: laminated composites, PVC foam sandwiches, aluminium foam and honeycomb sandwiches. Aim of this paper was the analysis of low-velocity impact response of such composites and the investigation of their collapse modes. Low velocity impact tests were carried out by a drop test machine in order to investigate and compare their structural response in terms of energy absorption capacity. The failure mode and the internal damage of the impacted composites have been, also, investigated using 3D Computed Tomography

Titanium Lattice Structures Produced via Additive Manufacturing for a Bone Scaffold: A Review

The progress in additive manufacturing has remarkably increased the application of lattice materials in the biomedical field for the fabrication of scaffolds used as bone substitutes. Ti6Al4V alloy is widely adopted for bone implant application as it combines both biological and mechanical properties. Recent breakthroughs in biomaterials and tissue engineering have allowed the regeneration of massive bone defects, which require external intervention to be bridged. However, the repair of such critical bone defects remains a challenge. The present review collected the most significant findings in the literature of the last ten years on Ti6Al4V porous scaffolds to provide a comprehensive summary of the mechanical and morphological requirements for the osteointegration process. Particular attention was given on the effects of pore size, surface roughness and the elastic modulus on bone scaffold performances. The application of the Gibson-Ashby model allowed for a comparison of the mechanical performance of the lattice materials with that of human bone. This allows for an evaluation of the suitability of different lattice materials for biomedical applications

Fatigue life prediction of high strength steel welded joints by Energy Approach

AbstractTwo full-field techniques were applied for the study of the base material and welded specimens, made of S690QL steel: digital image correlation and thermographic techniques. Static and fatigue tests were carried out. The thermographic measurements can be used to predict the fatigue, with a great saving in time and effort. Fatigue tests at increasing loads were carried out by a stepwise succession, applied to the same specimen, for applying an energy-based approach. The predictions of the fatigue life, obtained by means of the Energy Approach, were compared with the values obtained by the traditional procedure

aluminum honeycomb sandwich for protective structures of earth moving machines

Abstract The design and the assembly of the vehicles subjected to the risk of crushing from falling objects have to consider such danger and provide the operators with suitable safety systems. Generally, falling object protective structures for earth moving machines consist of vertical elements, connected by transversal elements, covered by a roof. The latter has the aim to protect the operators from falling objects and it is usually made of a steel skeleton with a metal plate. In this study, sandwich panels were proposed as technical solution for the impact protection from falling objects in earth moving machines. A very light and cheap aluminum honeycomb core (AA3003 alloy and cell size = 19 mm) was considered as design solution and was subjected to static and dynamic full-scale tests. The results were analysed according to the performance requirements of ISO 3449 standard. The experimental results confirmed that the honeycomb structures are well suitable for designing absorber devices in vehicles protective structures in order to ensure occupant safety

computed tomography analysis of damage in composites subjected to impact loading

The composites, used in the transportation engineering, include different classes with a wide range of materials and properties within each type. The following different typologies of composites have been investigated: laminated composites, PVC foam sandwiches, aluminium foam and honeycomb sandwiches. Aim of this paper was the analysis of low-velocity impact response of such composites and the investigation of their collapse modes. Low velocity impact tests were carried out by a drop test machine in order to investigate and compare their structural response in terms of energy absorption capacity. The failure mode and the internal damage of the impacted composites have been, also, investigated using 3D Computed Tomography

Experimental investigation on Iroko wood used in shipbuilding

The paper deals with investigations about mechanical properties of Iroko, a hardwood species used for structures in shipbuilding as glued laminated timber. Experimental tests have been carried out to assess strength, stiffness and density of Iroko in accordance with current EN Standards. All the results obtained by tensile and three-point bending tests, along with the statistical analyses performed to define the characteristics values of some mechanical properties, are reported in the paper. These values allowed to assign the strength class, reported in EN 338 Standard, to the investigated Iroko wood population. The experiments have taken into account both solid timber strips and scarf-jointed strips, in order to evaluate the influence of such a type of joint, which is widely used in wooden shipbuilding on strength and stiffness. Eventually, peculiar investigations have been carried out to analyse the failure mode of some test pieces through special experimental techniques: three-dimensional computed tomography and infrared thermography

investigation of very high cycle fatigue by thermographyc method

Nowadays, many components and structures are subjected to fatigue loading with a number of cycles higher than 107. In this scientific work, the behaviour of two kinds of tool steel was investigated in very high cycle fatigue regime. The fatigue tests were carried out at the frequency of 20 kHz and in fully reversed tension- compression mode (R = -1) by means of an ultrasonic fatigue testing equipment. The radiometric surface temperature was detected during all the test by means of an IR camera in order to extend the Thermographic Method and the Energetic Approach in very high cycle fatigue regime. The failure mechanism of the investigated steels was evaluated by means of several experimental techniques (scanning electron microscopy, Energy Dispersive X-ray spectroscopy and Optical Microscopy)

Experimental and theoretical analyses of Iroko wood laminates

This paper reports the experimental tests, which have been carried out to assess the mechanical properties of Iroko wood laminates used for the construction of a large wooden sailing ship. Three-point bending tests have been carried out on different types of specimens: laminates with 3 layers @ 0\ub0 and without scarf joints, laminates with 3 layers @ 0\ub0 having the outer layers with scarf joints, and laminates with 4 layers @ 0\ub0/\ub145\ub0/0\ub0 and no scarf joints. The tests have been performed in compliance with the current EN Standards. The analyses of the experimental data allowed the assessment of the mechanical properties of the laminated Iroko wood as well as the influence of scarf joints. The experimental results demonstrated that the presence of scarf joints only affect the strength of the glued laminate, while the stiffness properties in terms of Young modulus in bending and shear modulus, obtained applying the \u201cmethod of variable support span\u201d, remain essentially the same. The investigated laminates have been also analysed using a 3D computed tomography and an ultrasonic phased array equipment in order to assess the dimensions of possible defects or voids in the adhesive and the dynamic modulus of elasticity. The tomographic measurements of the glue thickness explained the reason of the reduced strength of the scarf joints, due to the inhomogeneity of the glue bond-line. The value of the dynamic modulus of elasticity, obtained by the ultrasonic technique, is slightly higher than the value of the modulus of elasticity obtained by the bending tests. Finally, the experimental findings have been compared with those drawn from both Classical Lamination Theory and Dietz approach, obtaining a good agreement and confirming that the Dietz approach is a fast and easy way to assess the elastic properties of a laminated structure

VALUTAZIONE DEL COMPORTAMENTO ALL’IMPATTO DI BIOCOMPOSITI RINFORZATI CON FIBRE DI AGAVE

The growing attention on environmental issues has led to a recent research interest in eco-sustainable and renewable materials, among which biocomposites play an important role. Biocomposites are materials consisting of a matrix with low environmental impact or renewable, reinforced with natural fibres. Several research activities reported in literature, deal mainly with the static mechanical properties. Just few works are instead devoted to the assessment of their dynamic properties, such as fatigue strength, impact strength, etc. In order to give a contribution to the knowledge of the impact behaviour of green epoxy matrix biocomposites reinforced with agave fibres, in this paper a systematic study is carried out to evaluate the impact strength of different laminates (single layer, cross-ply, quasi-isotropic), by low velocity impact test. The various selected laminates, allowed to assess the effects of the main influence parameters as fibre distribution (unidirectional and random), fibre concentration and lay-up