Study On Measurement And Evaluation Method Of Carbon Fibre Reinforced Composites Cutting Surface Roughness

Carbon fiber reinforced plastic composite (CFRP) have been widely used in aeronautics & astronautics. These advanced composite materials have advangeds in their superior specific modulus, surperior specific strength, wear resistance and high temperature resistant.Because of the inhomogeneous structure and anisotropy performance for fiber reinforced composite, its cutting mechanism is different from that of common engineering material, which leads to much special surface topography. However, at present detection and evaluation used for isotropic metal surface is also adopted in the design and application of composite, which cannot reflect the machined surface topographical characteristic of composite authentically. It is necessary to study on assessing the machined surface topography of composite. In this paper, C/C,C/Ph composites are studied. The 3D measurement method is studied on to assess the cutting surface topography of composite, so as to reflect it more authentically. The main studies are as follows:(1) The study on surface measurement method and the expariment of cutting for CFRP: The 3D measurement model is estabilshed. Distinguishing the two measurement methods by the contact stylus and the non-contact laser, the latter is chosen. The measurement steps are determined. The expariments of cutting are designed basend on the structure and cutting mechanism, through the effects of the cutting paremeters on the cutting surface of CFRP composite, the proper cutting speed, feed rate and depth of cut, the corner radius and material of the cutting tool are determined. The differences between the CFRP cutting and the metal materials cutting are discussed.(2) The study on the sample conditions in 3D measurement for CFRP:Determination of sample conditions is of great influence to the surface assessment of microscopic geometry error. Aiming at the uncertainty of selecting sample conditions depending on user's own experience in reality, one method that can determine appropriate sample conditions objectively is developed, that is applied for the measurement of surface of C/C,C/Ph composites. A normalized proximity factor is proposed to determine proper sample conditions. Results indicate that it is improper to measure all surfaces with one unique sample space for different C/C,C/Ph composite cutting surfaces. The average of the Sa,Sq,Ssk,Sku and maximum of St,Sp,Sv are proper to evaluat the cutting surface of the CFRP.(3) The study on the 3D evaluation method:With studying on 2D evaluation,3D evaluation for machined surface roughness of C/C,C/Ph composite and metal. The results indicate that:the topography of the composite is anisotropy, there are not obvious feeding textures in surface of composite, and there are abrupt peaks and valleys in surface, it appeared easily with the unique surface topography characteristics such as fiber pull-out, fiber crushing, fiber tearing, et al. The composite surface is evaluated using 3D evaluation method, the roughness error is small, and the unique topography characteristics can be authentically evaluated.Through analysis of the evaluation results, comparied the Sa, the prefer amplitudes parameter is Sg, Symmetry of the distribution curve of depths Ssk and flatness of the distribution curve of depths Sku indicate the characteristics of peaks ans valleys; Length of the fastest decrease Sal and ratio of texture aspect Str indicate the characteristics of the texture.; Density of tops Sds indicates the dictance of the spation; The autocorrelation curve indicates the period characteristics; The interactive abbott curve indaicates the characteristic of the bearing.(4) Study on topography of CFRP machined surfaces based on fractal theory:The fractal dimension is closely related 3D topography of the machined surfaces of composite. In order to analyze the local topography characteristic of C/C composite cutting surfaces, multifractals spectrum is introduced. The results indicate that:multifractals spectrum is related to 3D topography of cutting surfaces of C/C composite, the range of Lipschitz regularity reflects the roughness of surface, value of the multifractals spectrum reflects the distribution of the peaks and valleys of cutting surface. Compared with the 3D roughness evaluation by Sq and Sal, multifractals spectrum can evaluate the topography characteristic of composite, that is comprehensively authentically evaluated method.(5) The 3D evaluation on the C/Ph composite cutting surface in different cutting parameters:The C/Ph composite composite are cut in different cutting parameters (feed, velocity, depth of cut) tool material, the cutter corner radius. Thtough the cutting surface separately evaluated by 3D evaluation parameters, the 3D evaluation methods are validated on the C/Ph composite.