關(guān)于效應(yīng)的纖維濃度、溫度及模具厚度及其在完整熔接線性的共聚物復(fù)合材料#中英文翻譯#外文翻譯匹配

寧波大紅鷹學(xué)院 畢業(yè)設(shè)計(jì)（論文）外文翻譯 所在學(xué)院： 機(jī)械與電氣工程學(xué)院 班 級(jí)： 09 機(jī)自 3 班 姓 名 ： 陳慈航 學(xué) 號(hào)： 091280302 指導(dǎo)教師 ： 賈 濤 合作導(dǎo)師 ： 2012 年 10 月 7 日 Effect of fibre concentration, temperature and mould thickness on weldline integrity of short glass-fibre-reinforced polypropylene copolymer composites Abstract The effect of fibre concentration, temperature and mould thickness on tensile strength of single- and double-gated injection-moulded polypropylene copolymer reinforced with 0, 10, 20, 30 and 40 wt% short glass fibre was studied at a fixed strain-rate of 7.58 103 s1 between 23 and 100 C. It was found that tensile strength of single-gated mouldings, c, increased with increasing volume fraction of fibres, f in a nonlinear manner and decreased with increasing temperature in a linear manner. However, for f values in the range 010% a simple additive rule-of-mixtures adequately described the variation of c with f over the entire temperature range 23100 C studied here. Tensile strength of double-gated mouldings like their single-gated counterparts decreased linearly with increasing temperature. The presence of 熔接 significantly reduced tensile strength of double-gated composite mouldings but had little effect on tensile strength of the matrix. Weldline integrity factor, F , defined as weldline strength divided by unweld strength, decreased with increasing f but increased with increasing temperature. A linear dependence was found between F and temperature. Mould thickness had no significant effect upon weld and unweld tensile strengths and consequently had no significant effect upon weldline integrity factor. Introduction Tensile strength of short fibre composites is derived from a combination of the fibre and matrix properties and the ability to transfer stresses across the interface between the two constituents. Tensile strength is affected by a number of parameters, most importantly, concentration, length and orientation of the fibres as well as the degree of interfacial adhesion between the fibre and the matrix 112. However, as most short fibre composites are fabricated by an injection-moulded process, a major design concern is the effect that 熔接 may have on tensile strength of the polymer matrix and its composites. 熔接 are observed in injection-moulded components due to multigate moulding, existence of pins, inserts, variable wall thickness and jetting and are classified as either being cold or hot. A cold weldline is formed when two melt fronts meet head on and this type of weldline is the worst-case scenario as far as tensile is concerned. A serious reduction in strength has been reported for many polymers and their composites in the presence of cold 熔接 19. However, very little information is available regarding the influence of temperature and to some extent mould thickness on weldline strength and therefore the integrity of the welded components. To this end, this study was undertaken to examine the influence of temperature and mould thickness on weld and unweld tensile strengths of injection-moulded short glass-fibre-reinforced polypropylene copolymer (PPC) composite with fibre concentration in range 040 wt%. Experimental details Materials Polypropylene copolymer and its composites containing 10, 20, 30 and 40 wt% short glass fibres were supplied by PolyOne in the form of injection-moulded compounds. Injection moulding Materials were injection moulded in a Klockner Ferromatik F-60 injection-moulding machine at the processing conditions listed in Table 1 to produce a series of dumbbell-shaped test specimens. The moulds used consisted of a single-gate (SG) and a double-gate (DG) cavities as illustrated in Fig. 1 with nominal dimensions 4 10 120 mm3 and 1.5 10 120 mm3 (thickness, width and length, respectively). In the case of double-gated cavities, the two opposing melt fronts met to form a cold weldline approximately mid-way along the gauge length of the specimen. Table 1 Processing condition for injection-moulded PPC and its composites Processing condition 0 wt% 10 wt% 20 wt% 30 wt% 40 wt% Barrel temperature (C) Nozzle 220 220 220 210 220 Zone 2 210 210 210 207 210 Zone 3 210 210 210 207 210 Zone 4 210 210 210 207 210 Mould temperature (C) 30 30 30 30 30 Injection pressure (%) 95 95 95 95 95 Injection speed (%) 85 85 85 85 85 Cooling time (s) 15 15 15 15 15 Fig. 1 Single- and double-gated cavities with nominal dimensions of 4 10 120 mm3 (thickness, width and length, respectively) Differential scanning calorimetric (DSC) Thermal characterisation was carried out by DSC using a Perkin-Elmer DSC-6 modulated instrument. Samples of PPC and PPC composites, in the range 910 mg, were cut from the injection-moulded specimens and submitted to the thermal cycles of heating from 60 to 220 C at 10 C/min and cooling from 220 to 60 C at 5 C/min to obtain crystallisation data. The DSC curves were used to obtain the melting temperature (T m), crystallisation temperature (T c), enthalpy of crystallisation (H c) and the enthalpy of melting (H m). Values of H c, H m and percentage crystallinity ( c) were calculated from the following relationships: (1a) (1b) (1c) where is the heat of fusion for 100% crystalline polypropylene taken as 148 J/g and w p is the weight fraction of PPC in the composite (w p = 1 for 100% PPC). Fibre concentration and length measurements The exact weight fraction of the fibres in as received compounds (ARC) and in injection-moulded dumbbell specimens (IMDS) was determined by ashing a pre-weighed amount of material in a muffle furnace at 550 C for at least 1 h. After cooling, the remnant was weighed and weight fraction of fibres w f was determined. It can be seen from Table 2 that the measured weight fractions for both ARC and IMDS are within 1% of the manufacturers specification. Table 2 Fibre concentration and the average fibre lengths in ARC and in IMDS Composites PPC PPC PPC PPC 10% w/w GF 20% w/w GF 30% w/w GF 40% w/w GF ARC (%w/w) 9.50 20.03 30.05 39.70 IMDS (%w/w fibre) 8.60 20.10 28.30 39.70 Density (kg m3) 960 1030 1130 1220 %v/v (IMDS) 3.80 8.10 13.30 19.20 Average fibre length, ARC (mm) 0.389 (485) 0.353 (453) 0.350 (500) 0.347 (492) Average fibre length, IMDS (mm) 0.374 (534) 0.326 (479) 0.309 (424) 0.281 (400) Reduction in fibre length (%) 5 8 12 19 Values given in the parenthesis are the total number of fibre lengths measured The measured weight fractions, w f, were subsequently converted into volume fractions, f, using Eq. 2: (2) Table 2 shows values of f obtained via Eq. 2, taking density of glass fibre, f, as 2540 kg m3 and composite densities, c, as provided by the manufacturer. The ashes of fibrous material were subsequently spread on glass slides and placed on the observation stage of a microscope. Approximately 500 fibre lengths were measured for each composite (ARC and IMDS) using an image-processing system. From the fibre-length distributions examples of which are given in Fig. 2, the effect of fibre concentration and processing conditions on the average fibre length (L f) was assessed. Fig. 2 Fibre length distribution in IMDS Tensile tests The effect of fibre concentration, moulding thickness and temperature on weld and unweld tensile strengths was studied using an Instron testing machine. All the tests were performed at a constant crosshead of 50 mm/min (strain-rate of 7.58 103 s1). At least six specimens were tested for determining an average value. Results and discussion Analysis of DSC thermograms shows that melting temperature (T m) of the PPC matrix is not affected by the addition of fibres or by the heating cycle. However, as shown in Table 3, the heat of fusion (H m) in the second heating cycle is always greater than in the first heating cycle, and much closer to H c value. It is also evident that H m and H c both decrease initially with increasing fibre concentration showing similar trend to that of the percentage crystallinity (c) versus fibre volume fraction (f) as shown in Fig. 4. The striking feature of Fig. 3 is higher, c, for composite containing 30 wt% fibres, being 9% higher than for the unreinforced PPC. Table 3 Thermal analysis results for PPC and PPC composites w f (%) T m (C) T c (C) H m (J/g) H c (J/g) % c 1st cycle 2nd cycle 1st cycle 1st cycle 2nd cycle 1st cycle 0 163.44 166.47 119.25 85.85 89.69 91.61 60.60 10 165.56 166.30 130.92 75.92 85.06 87.94 57.47 20 165.41 165.76 129.99 74.16 84.75 82.86 57.26 30 164.89 165.12 129.47 84.46 97.74 99.64 66.04 40 164.43 164.82 130.92 75.20 88.07 88.07 59.50 Fig. 3 Effect of fibre concentration on percentage crystallinity The average length of the fibre length, L f , in IMDS and ARC are compared in Fig. 4 as a function of fibre concentration, f. It can be seen that L f in IMDS is consistently lower than in ARC. It is also evident that fibre concentration plays a major role in the shortening of the fibres particularly in IMDS where reduction in L f due to processing increases from 5 to 19%, as fibre concentration increases from 10 to 30 wt%. This reduction in fibre length with increasing f is attributed to increased probability of fibrefibre and fibremachine interactions as well as increased in the apparent melt viscosity which gives rise to higher bending forces on the fibres during moulding. Fig. 4 Effect of fibre concentration and injection moulding on the average fibre length in PPC composites Effect of fibre concentration, temperature and mould thickness on tensile strength of single-gated mouldings (unweld strength) Single-gated mouldings (i.e. unweld specimens) failed after exhibiting a clear yield point referred to in the following text as tensile strength. It was also noted that whist tensile strength increased, elongation to failure decreased, with increasing fibre concentration. This behaviour was consistently observed over the entire temperature range considered here. The effect of fibre volume fraction, f, on tensile strength of single-gated mouldings, c, at test temperatures ranging from 23 to 100 C is shown in Fig. 5. Results indicate that unweld tensile strength, c, increases nonlinearly with increasing f and therefore does not conform to rule-of-mixtures for strengths. The data presented here, as for many polymer composite systems 4, 5, 10, can best be treated using a second-order polynomial function of the form: (3) Fig. 5 Effect of fibre volume fraction on tensile strength of single-gated mouldings at 23, 40, 60, 80 and 100 C The polynomial functions describing the data in Fig. 5 are given in Table 4. These polynomials may be used to obtain some indication of the optimum value of f (i.e. f,max) for achieving the maximum tensile strength, at a given temperature. Values of, f,max, calculated at dc /f = 0, suggest that it is advantageous to increase the fibre concentration in the composite up to 2832% by volume. However, the processing difficulties and the possible strength loss due to fibrefibre interactions at high fibre concentration may limit the optimum value of f below that of f,max. Table 4 Polynomial functions for tensile strengths and the optimum volume fraction of fibres for single-gated mouldings at various temperatures Temperature (C) Polynomial function f,max 23 0.32 40 0.32 60 0.30 80 0.28 100 0.28 Figure 6 shows the data in Fig. 5 re-plotted for fibre concentration values in the range of 030 wt%. Clearly, within this range c is a linear function of f (regression coefficients R 2 = 0.996) and therefore it is reasonable to suggest that within this range, variation of c with f conforms to rule-of-mixtures for tensile strengths as given by Eq. 4. (4) Fig. 6 Effect of fibre volume fraction on tensile strength of single-gated mouldings at 23, 40, 60, 80 and 100 C for fibre concentration values in the range 030 wt% In the above equation, f and m are tensile strengths of the fibre and the matrix, respectively. The term s is fibre efficiency parameter taking into account the effects on composite strength due to shortness of the fibres and their misalignment in the moulded specimen. Rearranging Eq. 4 gives (5) The average values of s as obtained from the slope of the linear regression lines in Fig. 6 with f = 2470 MPa are plotted in Fig. 7 as a function of temperature. As can be seen s decreases linearly (R 2 = 0.998) with increasing temperature, thus indicating that fibres becoming less efficient as reinforcing fillers as temperature increases. The temperature dependence of s can be expressed as: (6) where = 0.192 and B = 1.28 103 C1. Fig. 7 Effect of temperature on fibre efficiency parameter, s for unweld tensile strength The effect of temperature on c is shown more explicitly in Fig. 8 where it can be seen that c decreases linearly with increasing temperature. The effect of increasing f is an upward vertical shift in ctemperature curve. The effect of temperature on c can be expressed as: (7) where A and B are dependent upon volume fraction of fibres. The slope of the lines in Fig. 8 (i.e. B = d/dT) are plotted in Fig. 9 as a function of f where it can be seen that variation is reasonably linear (R 2 = 0.983) and therefore can be expressed as: (8) where A = 0.24 MPa C1 and B = 2.573 MPa C1 for the PPC composites under investigation. Fig. 8 Effect of temperature on tensile strength of single-gated mouldings for composites containing 0, 10, 20, 30 and 40 wt% short glass fibres Fig. 9 Effect of fibre volume fraction on d/dT for both weld and unweld specimens The effect of mould thickness on c is shown in Fig. 10 as a function of f . Results show that mould thickness had little effect if any on the unweld tensile strength. This insensitivity to specimen thickness may be attributed to the fact that the average fibre length is much smaller than the mould thickness and therefore fibre orientation efficiency parameter, s, is unaffected by the mould thickness. Fig. 10 Effect of mould thickness on tensile strength of single-gated mouldings Effect of fibre concentration, temperature and mould thickness on tensile strength of double-gated mouldings (weldline strength) Stressstrain curves for double-gated specimens revealed that the presence of weldline in the double-gated mouldings reduces elongation at failure (i.e. ductility) and in the case of composites causes a significant reduction in both tensile strength and elongation at break. As illustrated in Fig. 11, for fibre concentration values in the range 010%, weldline strength, cw, decreases with increasing f at lower temperatures (T 40 C) but remains more or less independent of f at higher temperatures (T 40 C). At fibre concentration value of about 12% (corresponding to 30 wt%), cw shows a maximum value over the entire temperature range studied here; this value is higher than weldline strength of matrix material, mw. The striking similarity between the way in which percentage crystallinity and weldline strength vary with f implies that weldline strength is controlled to a large extent by the percentage crystallinity in the moulded specimens, i.e. increase in crystallinity increases weldline strength. Fig. 11 Effect of fibre volume fraction on tensile strength of double-gated mouldings at 23, 40, 60, 80 and 100 C 。 The effect of temperature