Papers by Keyword: Delamination

Abstract: The main objective of this work is to compare the different fracture behavior of carbon fiber-reinforced composite T300/epoxy with cross-play composite laminate. Tension-tension and three points bending fatigue are adopted, with optical microscopic and scanning electron microscopic observation of the specimen fracture surfaces. The specific objectives are: a) for tension-tension fatigue loading, the onset and multiplication of transverse matrix cracks continuously improve the delamination. Consequently, fibers rupture occurs in this locally region with high density of cracks. b) The density of intralaminar cracks increases with number of fatigue cycles. c) During the shear stress distribution under three points bending fatigue, delamination which is the main characteristic of T300/epoxy, initiates from the central and propagates alone the neutral axis of the sample. And a small quantity of fiber breakage occurs in the maximal compress region.

Abstract: Drill point angle of twist drill has a significant effect on thrust force and delamination factor on drilled holes in fiber reinforced polymer (FRP) composites. In this study, three drill point angle of twist drill; 85°, 118° and 135° were used to drill holes in hybrid fiber reinforced polymeric composite (HFRP). HFRP composites were fabricated using vacuum infusion molding (VIM) technique. The test samples were cured at 90°C for two hours. In drilling process various drill point angle and feed rate were employed to investigate the effect of both parameters on thrust force and delamination factor when drilling the HFRP composite. The results showed that small drill point angle and low feed rate can reduce the thrust force leading to the reduction of damage factor at the holes entrance and exit.

Abstract: Nowadays, sintering is a very useful technique to fabricate metal, ceramic and composites parts for different applications. This phenomenon has been extensively studied over 50 years and, most of the research related to it used a model based on two contacting particles. However, just a few jobs were focused on the powder sintering on a solid substrate. This work investigates the effect of two parameters; substrate shape and inclusion of the reinforced particles on the evolving microstructure during sintering of particles on a rigid substrate. Powders and solid bars of copper are used as a model material and particles such as tungsten carbide (WC) as reinforcing particles. Sintering was performed in an electrical furnace at 1050 °C under reducing atmosphere. The progress on sintering was evaluated by measuring the relative density close and far from the solid substrate by means of the image analysis from pictures taken by scanning electronic microscope (SEM). The effects on the constraint sintering were also identified. Heterogeneous densification and delamination of the film from the substrate were observed as densification increased which by the way is reduced by the inclusion of the reinforced particles.

Abstract: The evolution of carbon/epoxy composites use in aeronautics requires a better comprehension of the machining conditions influence on these materials. This study aim is to establish, based on the experimentation, the relationship between machining conditions and the behavior of drilled 2D and 3D carbon/epoxy composites. Two drill geometries, seam introducing and a range of cutting speed and feed have been tested. The effect of each parameter has been assessed in terms of thrust force, moment (recorded during machining) and defects (performed by macroscopic analyses and quantified using delamination factor F_d). Experimental results have shown significant influences of feed and drill geometry on delamination reduction. The use of a spur drill and a low feed generates minor defects and produces the best results. Furthermore, stitching helps reduce damage inside the hole.

Abstract: Failure develops and propagates through a structure via a complex sequence of competing micro-mechanisms occurring simultaneously. While the active mechanism of surface debonding is the source of loss of stiffness and cohesion, friction between cracked surfaces, upon their closure, acts as a passive dissipation mechanism behind the quasi-brittleness and hence can increase the toughness of the material under favorable loading conditions. In order to numerically study damage propagation, the constitutive response must be able to faithfully capture, both qualitatively and quantitatively, one of the signature characteristic of failure: the energy dissipation. In this paper, we present an interface decohesive model for discrete fracture that is able to capture the apparent enhancement of interfacial properties that is observed when transverse compressive loads are applied. The model allows to seamlessly account for the additional frictional dissipation that occurs when the loading regime involves transverse compression, whether during debonding or after full delamination. This constitutive model is then used to successfully predict the response of realistic engineering structures under generalized loading conditions as demonstrated with the numerical simulation of a fiber push-out test.

Abstract: This paper presents an experimental investigation into the mode I interlaminar fatigue resistance of carbon fibre-epoxy laminate reinforced in the through-thickness direction with z-pins. The effects of the volume content, diameter and length of z-pins on the interlaminar toughness, fatigue resistance and crack bridging toughening mechanisms are determined. The delamination growth rate also slowed when the volume content or length of the z-pins was increased or the z-pin diameter was reduced.

Abstract: The percentages of delamination of Compacted Bamboo Guadua were calculated using digital images processing. Three processes were done in the development of this project: tests of delamination, digital image pre-processing and digital image processing of the images acquired. The test of delamination followed the ASTM 5824. The digital image pre-processing was supported on the acquisition of sequences of images, doing a sweeping of the samples, and finally the digital processing worked in the generation of panoramas with sequences of images acquired from the sample. Additionally, the total area from the sample was measured digitally, the segmentation and the measurement of delamination area were done, finding the ratio between the delamination area and the total area of the sample, and obtaining the value of percentage of delamination per section. Digitally, the obtained values for samples made with fibers obtained from Stick (Varillón), Top (Sobrebasa), Middle (Basa) parts and mixture of them were 16.97%, 9.96%, 5.96% and 8.64% respectively.

Abstract: This paper presents the mechanical properties measured on glued laminated pressed guadua samples. Experimental tests like shear parallel to fiber, tensile and shear perpendicular to fiber and flexural tests were carried out using three different types of adhesives: European Melamine Urea Formaldehyde, Colombian Melamine Urea Formaldehyde, and Polivinil Acetate humidity resistant. In order to study the behavior of the material in aggressive environmental conditions, half of the samples used in the mechanical tests were introduced in a temperature and humidity chamber for 45 days set to 45°C of temperature and 95% of relative humidity, usual environmental conditions in Chocó Colombia.The results showed that the highest values of mechanical strength were obtained for samples made with European Melamine Urea Formaldehyde. In addition, it was found that this adhesive was the one with better behavior under the aggressive environmental conditions simulated.

Abstract: Machining of Carbon Fibre Composite (CFC), particularly drilling is frequently employed in many industries especially when dealing with joining, assembly and structural repair of the parts. This paper summarizes the properties of the CFC as well as the appropriate material and geometry of the cutting tool that should be used when drilling of the CFC in order to optimize the drilling performance. In addition, this work also presents the literature review on the relationship between cutting speed, feed rate, tool wear, thrust force and damage of the drilled CFC. The nature and heterogeneous structure of CFC often resulted in difficulty during their machining in terms of rapid tool wear and high thrust force. As a result, this always results in the damage of the drilled parts. Furthermore, higher cutting speed and lower feed rate are also recognized as significant factors which contribute to rapid wear of the cutting tool. Therefore, the use of tungsten carbide cutting tools, cutting fluids and cryogenic machining is seen to be a practical technique in optimizing the drilling performance involving CFC. In general, this work intends to provide a basic guideline and understanding regarding drilling of the CFC.

Abstract: The static and cyclic failure mechanisms of offshore pipe riser repaired with a designated laminate orientation of carbon/epoxy (C/E) system were studied. The finite element (FE) model takes into account failure mechanisms of the composite sleeve inter-layer delamination, debonding at the steel riser-composite surface interface, and the maximum permissible strain of the repaired riser. Design conditions of the combined static loads (coupled internal pressure, longitudinal tensile and transverse bending) were determined through a limit state analysis [1,2]. The limiting static bending load that causes catastrophic failure under a coupled internal pressure and tensile loadings was determined through Virtual Crack Closure Technique (VCCT). The effects of cyclic bending, mimicking the typical scenarios experienced in pipe riser exposed to dynamic subsea environment, were evaluated and compared against the static conditions. The low cycle fatigue of the composite repair system (CRS) is simulated using a direct cyclic analysis within a general purpose FE program, where the onset and fatigue delamination/disbonding growth are characterized through the Paris Law.