JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011 - 50

simulation
measurements The L-shaped T300/914 composite parts are manufactured using laboratory facilities (Figure 1). Sixty plies of 150x200 mm unidirectional pre-impregnated material are cut to produce two L-shaped composite parts. The prepared plies are placed onto the "tool" mould half and stacked with a [0, 90]30 stacking sequence. The second mould half is adjusted by means of four screws. A torque wrench is used to ensure proper tightening. The space between both mould halves (9.5 mm) is verified with a Vernier caliper. Fig. 2: (a) Notation for the angles and planes of reference; (b) benchmarks used for angular

supplied by Hexcel Composites are used in this study. The nominal ply thickness is 0.158 mm, the resin density is 1.30 g/cm3, the nominal fibre volume is 59% and the fibre density is 1.76 g/cm3. The model used to represent the material response postulates that the liquid resin and dry fibre preforms are separate entities. The dry fibre is assumed to be simply elastic, while the impregnated fibre is considered as a viscoelastic medium. In order to simulate the manufacture of the model composite, data are needed in both the rubbery and glassy states. This is achieved from the constituent properties. Once the resin and fibre properties are known, the equivalent ply properties of T300/914 can be calculated using the standard mixture equations. More precise data for the T300/914 material can be found in ref. [2].

inner and outer angles between the two wings of the L are 90°. Figure 2 (a) shows the notations for both spring-in angles and four planes, Figure 2 (b) highlights the benchmarks used for angular measurements.

Manufacturing process

The typical cure cycle for this kind of material is applied: the oven is heated to 175°C at a rate of 5°C/min, with a temperature dwell time of 60 minutes, then cooled down to room temperature. Freestanding is used as a cooling process. The temperature is measured throughout the manufacturing process by means of a thermocouple which is in contact with the tool surface of the Lshaped part.

Measurements

The dimensional measurements are made to check the conformity of the composite part and to understand the origin and consequences of the material reaction to its manufacturing conditions. In the ideal case for an L-shaped composite part, the

jec composites magazine / No67 August - September 2011

Fig. 1: L-shaped composite part in the AU4G aluminium mould before curing

The angle variations are measured with a 3D coordinate measuring machine (CMM). The CMM has a touch-trigger (or tactile) probe with a special tip that is used to touch various spots on the part being measured. By precisely recording the X, Y, and Z coordinates of the target, points are generated which can then be analyzed via regression algorithms.

Experimental results
The mould surface flatness defect is measured (3.4 μm) before starting the angular measurements. Two new parameters are introduced here, and , which are the difference between the targeted 90°and, respectively, β and α. Figures 3(a) and 3(b) show the angular variations of both composite parts. It can be seen that is higher than . The same trend was observed for Fig. 3: Spring-in angles with respect to the benchmarks: carbon/epoxy, (a) part 1, (b) part 2 with a composite part of similar geometry, by Qi et al. [7]. In the present case, is 28-56% higher than for the first part, and 1-22%

JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011