Compression moulding of glass and polypropylene composites for optimised macro- and micro- mechanica
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Composites Science and Technology 59 (1999) 1153±1167
Compression moulding of glass and polypropylene composites for optimised macro- and micro- mechanical properties 3. Sandwich structures of GMTS and commingled fabrics
 de  rale de Lau* Corresponding author, at: Ecole Polytechnique Fe sanne (EPFL), Laboratoire de Technologie des Composites et PolyÁ res (LTC), CH-1015 Lausanne, Switzerland. Tel.: +41-21-693-5995; me fax: +41-21-693-5880; e-mail: martyn.wakeman@ep¯.ch
or matrix is thought to occur. Processing of each class of materials in isolation was described in parts 1 and 2 of this series [1,2]. Sandwiches of GMTs with commingled fabric facings oer potential to increase the speci®c bending stiness of glass and polypropylene composites. This is shown schematically in Fig. 1. Placing skins of woven commingled glass and polypropylene yarns (balanced weave, 60% glass mass fraction) at the laminate surfaces maximises the displacement of the higher and aligned glass content from the laminate neutral axis. In this work, a 40 wt% GMT core was sandwiched between the skins, providing improved properties with respect to GMT and enhanced processability compared to fabric alone [3]. The GMT core damps potential thickness variations arising from the shearing but overall complexity is still thought to be restricted by the fabric shear compliance [4]. In areas where fabric is not required (or where the geometry precludes its use), the GMT can be used to ®ll local features and provide stiness via the section modulus. 1.1. Objectives Given the apparent potential for combining fabrics with ¯ow moulding materials, a study of the consolidation process was initiated. The speci®c aims were to:
0266-3538/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0266 -3 538(98)00155 -9
1ቤተ መጻሕፍቲ ባይዱ54
M.D. Wakeman et al. / Composites Science and Technology 59 (1999) 1153±1167
Abstract The co-moulding of random-reinforced GMTs with commingled E-glass and polypropylene fabrics was investigated in a series of experiments which were designed statistically. Materials were heated in an infra-red oven prior to non-isothermal compression moulding. Maximum preheat times and temperatures were determined by gel permeation chromatography to monitor the onset of degradation of the polymer matrix. Laminate properties were mapped according to the processing parameters and optimum conditions for consolidation were identi®ed. The process parameters were ranked in order of importance for maximum ¯exural modulus and time at pressure proved the most signi®cant factor. Microscopy was used to investigate the impregnation mechanisms and the subsequent removal of voidage. # 1999 Elsevier Science Ltd. All rights reserved.
M.D. Wakeman*, T.A. Cain, C.D. Rudd, R. Brooks, A.C. Long
Department of Mechanical Engineering, University of Nottingham, Nottingham, UK Received 14 January 1998; received in revised form 10 August 1998; accepted 14 September 1998
Fig. 1. Sandwich of commingled glass and polypropylene with GMT.
. Monitor (and optimise) the preheat cycle by measurement of polymer degradation. . Map the eects of process parameters on the laminate mechanical properties and microstructure and thereby to develop the conditions for optimal consolidation. By considering these results in the light of our previous studies for the two material forms in isolation, it was intended to learn how the process might dier, given the dierent boundary conditions involved. 2. Experimental details 2.1. Equipment The processing equipment is shown schematically in Fig. 2. A 4.5 kW R-Royce infra red oven was used to preheat the material blanks. A Bradley and Turton 150 tonne hydraulic moulding press was used to generate maximum pressures of 200 bar on the laminate, with electrically heated platens used to heat the press tooling. Computer control of the press enabled fast material transfer from the oven to press, typically less than 10 s, and the measurement of laminate thermal histories. An instrumented steel compression moulding tool with vertical telescoping shear edges was used to produce all of the mouldings in this study. 2.2. Materials The commingled fabrics, described in part 1 [1], consisted of a balanced weave fabric (Vetrotex Twintex2) of super®cial density 650 g/m2 woven from yarns of 60% by mass commingled E-glass and polypropylene. GMTs (Symalit GMT 40PP) consisting of 40% by mass continuous random glass mat reinforced polypropylene, described previously in part 2 [2], were used for the ¯owable core. Laminates of 300 mm diameter were produced from two GMT blanks, 171mmÂ171 mm, sandwiched between 2 blanks of fabric, 198mmÂ198 mm, to give a nominal thickness of 4 mm. The fabric blanks were cut from preconsolidated (0.92 mm) sheet. This formed a sandwich at the centre of the laminate and a pure GMT region at the
Compression moulding of glass and polypropylene composites for optimised macro- and micro- mechanical properties 3. Sandwich structures of GMTS and commingled fabrics
 de  rale de Lau* Corresponding author, at: Ecole Polytechnique Fe sanne (EPFL), Laboratoire de Technologie des Composites et PolyÁ res (LTC), CH-1015 Lausanne, Switzerland. Tel.: +41-21-693-5995; me fax: +41-21-693-5880; e-mail: martyn.wakeman@ep¯.ch
or matrix is thought to occur. Processing of each class of materials in isolation was described in parts 1 and 2 of this series [1,2]. Sandwiches of GMTs with commingled fabric facings oer potential to increase the speci®c bending stiness of glass and polypropylene composites. This is shown schematically in Fig. 1. Placing skins of woven commingled glass and polypropylene yarns (balanced weave, 60% glass mass fraction) at the laminate surfaces maximises the displacement of the higher and aligned glass content from the laminate neutral axis. In this work, a 40 wt% GMT core was sandwiched between the skins, providing improved properties with respect to GMT and enhanced processability compared to fabric alone [3]. The GMT core damps potential thickness variations arising from the shearing but overall complexity is still thought to be restricted by the fabric shear compliance [4]. In areas where fabric is not required (or where the geometry precludes its use), the GMT can be used to ®ll local features and provide stiness via the section modulus. 1.1. Objectives Given the apparent potential for combining fabrics with ¯ow moulding materials, a study of the consolidation process was initiated. The speci®c aims were to:
0266-3538/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0266 -3 538(98)00155 -9
1ቤተ መጻሕፍቲ ባይዱ54
M.D. Wakeman et al. / Composites Science and Technology 59 (1999) 1153±1167
Abstract The co-moulding of random-reinforced GMTs with commingled E-glass and polypropylene fabrics was investigated in a series of experiments which were designed statistically. Materials were heated in an infra-red oven prior to non-isothermal compression moulding. Maximum preheat times and temperatures were determined by gel permeation chromatography to monitor the onset of degradation of the polymer matrix. Laminate properties were mapped according to the processing parameters and optimum conditions for consolidation were identi®ed. The process parameters were ranked in order of importance for maximum ¯exural modulus and time at pressure proved the most signi®cant factor. Microscopy was used to investigate the impregnation mechanisms and the subsequent removal of voidage. # 1999 Elsevier Science Ltd. All rights reserved.
M.D. Wakeman*, T.A. Cain, C.D. Rudd, R. Brooks, A.C. Long
Department of Mechanical Engineering, University of Nottingham, Nottingham, UK Received 14 January 1998; received in revised form 10 August 1998; accepted 14 September 1998
Fig. 1. Sandwich of commingled glass and polypropylene with GMT.
. Monitor (and optimise) the preheat cycle by measurement of polymer degradation. . Map the eects of process parameters on the laminate mechanical properties and microstructure and thereby to develop the conditions for optimal consolidation. By considering these results in the light of our previous studies for the two material forms in isolation, it was intended to learn how the process might dier, given the dierent boundary conditions involved. 2. Experimental details 2.1. Equipment The processing equipment is shown schematically in Fig. 2. A 4.5 kW R-Royce infra red oven was used to preheat the material blanks. A Bradley and Turton 150 tonne hydraulic moulding press was used to generate maximum pressures of 200 bar on the laminate, with electrically heated platens used to heat the press tooling. Computer control of the press enabled fast material transfer from the oven to press, typically less than 10 s, and the measurement of laminate thermal histories. An instrumented steel compression moulding tool with vertical telescoping shear edges was used to produce all of the mouldings in this study. 2.2. Materials The commingled fabrics, described in part 1 [1], consisted of a balanced weave fabric (Vetrotex Twintex2) of super®cial density 650 g/m2 woven from yarns of 60% by mass commingled E-glass and polypropylene. GMTs (Symalit GMT 40PP) consisting of 40% by mass continuous random glass mat reinforced polypropylene, described previously in part 2 [2], were used for the ¯owable core. Laminates of 300 mm diameter were produced from two GMT blanks, 171mmÂ171 mm, sandwiched between 2 blanks of fabric, 198mmÂ198 mm, to give a nominal thickness of 4 mm. The fabric blanks were cut from preconsolidated (0.92 mm) sheet. This formed a sandwich at the centre of the laminate and a pure GMT region at the
