Papers by Keyword: CFRP

Abstract: In this study, effect of Carbon Milled Fiber (CMF) addition on flexural fracture property of Carbon Fiber Reinforced Plastics (CFRP) was investigated. The CMF additive amounts to the epoxy resin were 0.5wt%, 0.8wt%, 1.0wt% and 1.2wt%. Static three point flexural test was conducted based on Japanese Industrial Standard (JIS) K 7074. The in situ observation of CMF added CFRP was conducted by using high-speed camera. As a result, following conclusions were obtained. In case that CMF additive amount was below 0.8wt%, flexural strength and flexural modulus of CFRP increased with an increase of CMF additive amount. In case of that CMF additive amount was above 1.0wt%, flexural strength and flexural modulus of the CFRP decreased compared with those of CMF 0.8wt% added CFRP. From in situ observation, crack initiation occurred at external layer on tension side of non CMF and CMF added CFRP. After crack initiation, delaminations of non CMF and CMF added CFRP were found. The delamination size of CMF 0.8wt% added CFRP was smaller than that of non CMF and CMF 1.2wt% added CFRP. Therefore, flexural property of CFRP was improved because delamination of CFRP was prevented by CMF 0.8wt%.

Abstract: Carbon fiber reinforced polymers (CFRP) are getting more and more important for structural components for automotive and aerospace applications. These components are subjected to 10¹¹ and more loading cycles during their time in service. Therefore the VHCF behavior and the corresponding failure mechanisms have to be well understood. To obtain a comprehensive knowledge about the fatigue behavior and failure mechanisms of CFRP in the VHCF regime, a new Ultrasonic Testing Facility (UTF) for cyclic 3-point bending at 20 kHz has been developed at WKK. This UTF with combined online nondestructive testing via laser vibrometry and IRthermography enables VHCF experiments up to 10⁹ cycles in twelve days without overcritical heating up to the glass transition temperature of the polymer. The chosen material in this research project is the commercially available and aircraft qualified carbon fiber fabric reinforced polyphenylensulfide (CF-PPS). To determine the fatigue characteristics of CF-PPS load increase tests and based on these results constant amplitude tests up to 10⁹ cycles have been carried out. Light optical and SEM microscopy have been performed in defined fatigue states or finally after reaching 10⁹ cycles with shear stress amplitudes of at least 44% of the monotonic ultimate shear strength. The induced fatigue damage of CF-PPS in the VHCF regime was studied in detail.

Abstract: Modern lightweight construction containing hybrid materials and structures allow the improvement of a wide range of density specific properties. In this regard, the great potential of structures consisting of carbon fibre reinforced plastics (CFRP) and aluminium (Al) is far from being exhausted. In order to exploit this potential, novel joint concepts are necessary, enabling simultaneously an economic structure manufacturing. As a more advantageous alternative to conventional riveting, the development of integral joint concepts with material oriented design that includes high load capacity and improved corrosion resistance has currently high priority for aviation industry. The research group Schwarz-Silber (FOR 1224) funded by the Deutsche Forschungsgemeinschaft (DFG) and based at the University of Bremen set itself the goal to explore and develop interface structures for advanced CFRP-Al compounds. Considering textile, welding and casting techniques, novel joint concepts will be designed, dimensioned and produced within six interdisciplinary projects. Experimental and numerical investigations support the validation and enhancements of the developed solutions. Regarding a joint concept combining textile and welding techniques, basic investigations have been performed. The concept of coupling Al sheets with CFRP panels by means of transition structures made of titanium (Ti) sheets, being bonded to the CFRP side and welded to the Al side, has already been analysed under static tensile loads. This paper presents the failure behaviour of such entire Al-Ti-CFRP joints under cyclic loads. The failure probability is calculated by using the approach of maximum likelihood.

Abstract: This study focuses on the flexural behavior of timber beams externally reinforced using Carbon Fibre Reinforced Plastics (CFRP). A non-linear finite element analysis is proposed in order to complete the experimental analysis of the flexural behavior of the beams. An elasto-plastic behavior is assumed for reinforced Timber and interface elements are used to model the interaction between CFRP and timber.The predicted and measured load–midspan deflection response results in addition to the failure modes are compared. It was observed that the predicted FE results are in good agreement with the experimental measured test data.

Abstract: We examined the relation between the cutting force and the cutting characteristics of CFRP in diamond saw cutting. When a larger cutting force was applied, the cutting had been propagated with a mixed mechanism of the cutting by cutting edges and the cleaving of carbon fiber by shear force. While a good cutting surface was formed in the case of cutting with less than 23 N of cutting force. In this condition, the cutting had been propagated only by the cutting with cutting edges.

Abstract: CFRP and Titanium alloy, which are known as difficult-to-cut materials have been widely used as structural material in aviation industries. The orbital drilling is one of an effective drilling technique for the industries. However this technique has some disadvantages such as increase of cutting force due to cutting with tool center point, inertial vibration generated by revolution and high installation cost. In order to improve the disadvantages, we have invented a new drilling technique which is called inclined planetary motion milling. The inclined planetary motion milling and the planetary mechanism drilling has two axes of cutting tool rotation axis and revolution axis. Cutting tool rotation axis of the orbital drilling is moved parallel to the revolution axis in eccentric. On the other hand, in the case of the inclined planetary motion milling, eccentric of the cutting tool rotation axis is realized by inclination of a few degrees from the revolution axis. Therefore, the movement of eccentric mechanism can be reduced by comparison with the orbital drilling because inclined angle is smaller than eccentricity of the cutting tool tip. As a result, eccentric mechanism can be downsized and inertial vibration is reduced. In the study, a geometrical cutting model of inclined planetary motion milling was set up. The theoretical surface roughness of the inside of drilled holes by use of two types cutting tool geometry were calculated based on the model. And cutting experiments using the new prototype for CFRP were carried out in order to evaluate the effect on machinability with change of cutting point atmosphere. In addition, optimal cutting condition was derived according to cutting experiments for titanium alloys utilizing the orthogonal array.

Abstract: Recently, carbon fiber reinforced plastics (CFRP) are expected to be used more in the aerospace and automotive industries, because of their outstanding lightweight material characteristics and tensile strength [1][2]. Underlying this are problems closely related to improvement of the earth’s environment. However, a mechanical property is influenced by the difference in the distribution state of the carbon fiber, and the adhesion intensity of the binding material. Moreover, they have the characteristic of intense anisotropy, strength wise depending on the orientation of the carbon fibers [3][4]. Therefore, CFRPs are considered difficult-to-machine materials [5], because the surface finish deteriorates according to the carbon fiber orientation. Establishing the optimal cutting conditions to solve such problems also from an economical viewpoint is essential. In our study, end milling operations of different carbon fiber orientation CFRP composite material were investigated with three kinds of different helix angle end mills. Evaluations were based on the surface finish, cutting force and cutting temperature. Moreover, the relationships between the carbon fiber orientation and the machining operations were determined. We earlier evaluated the machinability from the relationship between carbon fiber orientation and tool helix angle by down-cut milling to solve these problems [6]. In this study, machining operations of different carbon fiber orientation CFRP composite material were investigated with three kinds of different helix angle end mills by up-cut milling. Evaluations were based on the surface finish, cutting force and cutting temperature. Moreover, the results of this experiment were compared with the results of down-cut milling.

Abstract: This paper presents experimental examples of machining damages resulting from a piercing process in CFRP laminates. A circular perforation was formed in CFRP cross-ply specimen with a punch jig using different blade angles and two distinct dimensional conditions. Surface, cross-sectional, and internal changes to the CFRP specimens after the hole-punching were observed using optical microscopy and X-ray analysis to quantitatively evaluate damage, including delamination, around the perforation area. Results indicate that the optimum piercing is achieved when the blades are parallel to fiber direction at an elevated temperature with blade angles essentially irrelevant.

Abstract: As the tendency towards weight reduction and low fuel consumption seems to drive the increased use of advanced exotic materials such as composites, titaniums and Inconels in the aerospace industry, the need for machining remains in aircraft industries as a post-processing operation. In the present work, the investigation of the influence of machining parameters on surface temperature when drilling CFRP using 4 mm-diameter 2-fluted carbide end-mill coated with diamond is presented. The temperature was examined on Thermal Gun Quicktemp 860-T1 sensor and analysed based on analysis of variance (ANOVA) of Central Composite Design of experiments and a first order mathematical model has been developed to predict temperature values for range of machining parameters used in the study. The relationship between the machining variables and output variables is established. It was found that the lowest temperature (32.2°C) was generated at rotational speed, 537 rpm and feed rate, 180 mm/min and at the highest temperature (39.1°C) generated at rotational speed, 4400 rpm and feed rate, 270 mm/min.

Abstract: This paper presents the investigation of the influence of machining parameters on delamination at entry of drilled holes after drilling into CFRP composite using 4 mm-diameter 2-fluted carbide drills coated diamond. The delamination at tool entry was analyzed in terms of delamination factor on the basis of analysis of variance (ANOVA) of Central Composite Design (CCD) of experiments. It is found that spindle speed is the most influential factor for the drilling of CFRP within the range of cutting parameters examined. The lowest delamination factor (1.006) was generated at rotational speed, 4400 rpm and feed rate, 270 mm/min; and the highest delamination factor (1.123) generated at rotational speed, 537 rpm and feed rate, 180 mm/min. A mathematical model has been predicted for the delamination at tool entry. The relationship between the machining variables and output variables is also established.