Abstract: Carbon fibre-reinforced plastics (CFRPs) gained substantial acclaim in recent decades and are used in aerospace, automotive and structural applications due to their high strength-to-weight ratio, high stiffness, high fatigue and corrosion resistance. CFRPs are manufactured near to net shape but some machining processes such as drilling cannot be avoided. Drilling induces damage (delamination, matrix cracking, matrix burning, lamina cracking and fibre pull out) in CFRP because of high axial thrust forces and a temperature rise. In this research an attempt is made to use ultrasonically assisted drilling (UAD) to reduce the axial thrust forces. In UAD high frequency (~ 20 kHz) vibrations are superimposed on a drill bit, preferably in axial direction, to reduce the thrust forces. In this study, experiments are conducted in two stages. At the first stage an initial setup with an existing UAD transducer is used to compare UAD with conventional drilling (CD) of CFRP. A reduced thrust force is experienced in case of UAD when compared to CD. At the second stage, drilling dynamics, i.e. feed speed, is changed along with the improvement of the transducer, and an enormous amount of force reduction (>80%) is observed in case of UAD (as compared to CD).
Abstract: Due to their good mechanical properties and short cycle times during processing, textile-reinforced thermoplastic composites gain increasing relevance for high-volume lightweight applications. Beyond that, by exploiting its specific processing capabilities, this composite material enables a variety of novel manufacturing techniques, e.g. for assembling. In this paper a joining technique is presented, which utilises the meltability of the thermoplastic matrix to establish a material-adapted joining method by introducing slender metallic pins into the composite structure. The processing principle is described and structural effects in the joining zone are analysed by means of microscopy. The load bearing behaviour is characterised by tensile tests on double-lap-shear specimen.
Abstract: Experimental research in both medical sciences and material science rely in many situations on a reduced quantity of available data, due to limited number of patients or high costs of samples. Some statistical data manipulation methods are discussed regarding their applicability, information content, value and limits. A special attention is given to the extreme values eliminated by the GRUBBS test. The necessity of the elimination of the extreme values is demonstrated.
Abstract: In this paper an inverse finite element procedure was developed to assess the true- stress strain relationship of a DP dual phase. Experiments were performed both by means of instrumented indentation and small punch tests on small samples cut in the same steel sheet. Tests are developed on a Zwick macro-hardness tester. Single test are first proposed in order to estimate the parameters of the constitutive law (K,n). We propose to conduct SPT tests using PTFE lubricant and hard (WC / Co) ball. An inverse method based on the Nelder and Mead algorithm has been developed in order to found experimental curves. Nevertheless we show that this method lead to poor estimation of the parameter of the constitutive law. We propose to improve these estimations by cross-mechanical tests. Indeed we show that the estimation of the low-error (K,n) domains deduced from each single test can be crossed. This method leads to a better estimation of the constitutive law. Moreover both load/displacement curves of SPT and macrohardness can be found again.
Abstract: The atomic force microscope (AFM) is a mechanical imaging instrument that measures the three dimensional topography at nanoscale as well as physical properties of a surface with a sharpened tip. This paper proposes an AFM imaging process for obtaining quality images in order to describe surface topography of different materials. Good topography information is a premise in nanoindentetion and in determining mechanical properties of materials. Samples used were: copper, nickel, titanium, polyamide and trabecular bone.
Abstract: This paper presents the size effect on fracture toughness of polyurethane foams (PUR 40), with nominal density 40 kg/m3, closed-cell rigid foams widely used for sandwich cores. Determination of the fracture toughness was carried out by three-point bending tests (TPB), on notched specimens, at room temperature (20±2°C). To determine the size effect in Mode I fracture toughness, specimens geometrically similar in two dimensions with length-to-width ratio 5:2 were selected. The specimens were subjected to a quasi-static loading with a speed of 2 mm/min, which was applied exactly on the notch direction. A strong size effect in the closed-cell PUR foam is experimentally demonstrated, by considering a smooth transition between strength of materials approach (with no size effect) and asymptotic case of linear elastic fracture mechanics.
Abstract: When subjected to external loading, polymeric materials behave in a manner intermediate between elastic solids and viscous fluids. Their mechanical properties depend on a material’s viscous flow, which, in turn, is influenced by (i) temperature, with its different magnitudes determining a ductile or brittle behaviour and (ii) time, through the effect of a deformation rate and long-term relaxation. Short-term viscoelastic properties (loss and storage moduli) of a studied semi-crystalline thermoplastic polymer were obtained using Dynamic Mechanical Analysis, while its long-term viscoelastic properties (compliances) were determined using creep tests.
Abstract: A three-dimensional crystal-plasticity finite element model of nano-indentation is developed in this paper to analyze deformation of a face-centred cubic (f.c.c.) high-purity single crystal of copper. This model was implemented as a user-deﬁned subroutine in the commercial finite element software ABAQUS/Standard and used to study cases with different crystallographic orientations of the single crystal. The effects of various factors – crystallographic orientation of the indented material, an indenter angle and contact conditions between the indenter and workpiece material – on the load-displacement characteristics are studied. The obtained results show an anisotropic nature of surface topography around the obtained indents.
Abstract: Adhesive bonding of two different materials appears in many modern engineering applications, e.g.: airplanes, boats, cars etc. In many practical problems the adhesive bonding is subjected to shear loading. Therefore this is important to investigate the whole deformation process of the considered type of joints under monotonic loading, to get information about the shear strength and strain concentrations. Such concentrations lead to microdefects initiation and their further coalescence to create a main crack. The unstable crack propagation leads to final failure of the adhesive joint. The Digital Image Correlation (DIC) System - ARAMIS allows for constant monitoring of the deformation state up to the final failure. The tests were performed for bi-material specimens made of adhesively bonded PMMA and aluminum strips (Fig.1) and for pure PMMA and pure aluminum specimens. Additionally, two strain gauges on each homogeneous specimen and four on the bimaterial ones are used for strains estimations. The four point bending Iosipescu tests were performed using MTS machine with constant speed. In the first method (DIC) the ARAMIS system recorded a displacement distribution in samples with frequency 1Hz. In the second method the strains were recorded by the strain gauges - using analog output channels of the HOTTINGER data Acquisition System - MGCPlus, the current value of the load using analog output channel of the MTS machine was recorded too. The load-displacement curves were obtained for the whole deformation process and the shear strength of the joints was estimated. The energy absorption of the joints was calculated.
Abstract: The present work shapes a normal plastic gear and simulates the corresponding worn one in order to predict its mechanical behavior in operation depending on the wear. To predict the mechanical behavior of plastic gears, a modeling of the gears has been done under SOLIDWORKS. Then with ALGOR, which uses the FEM, we studied two types of gear. A normal tooth of each type of gear has been net as well as the corresponding worn tooth. We opted for the study of two cases of charge. The first (case 1) corresponds to the application of strength to the head of the tooth (Fig. 2) and the second (case2) at the pitch point of the tooth (Fig. 3). We noticed the stresses and deformations on the nodes located on the right profile of the tooth, the first node is taken at the head of the tooth. The wear has been assumed uniform on the right profile from the head to the root. The tooth has been assumed embedded at the root. We obtained some results which could allow the prediction of the number of revolutions to breaking off, knowing the wear according to this cycle.