V. Cannillo et al. /Composites: Part A 37 (2006 )23-30 4. Results and discussion those treatments where the soaking temperature was 685 C namely treatments 1, 2 and 3 Fig. 2(a-c) illustrates the results obtained for each As regards the shrinkage, the effect of temperature, processing treatment in terms of diameter and thickness soaking time, pressure and reinforcement volume fraction shrinkage, and relative density(percentage of the theoretical can be evaluated. In particular, as previously observed, the value). These results show that treatments 7,8 and 9 are temperature of 885 C leads to an expansion in thickness; in unacceptable since the sample present an expansion in fact, such temperature coincides with the temperature of half-ball [16] of the frit used. In this condition, the viscosity Each output parameter, namely the diameter and becomes too low and spherical pores arise. The most thickness shrinkage and relative density, were separately suitable temperature for composites densification seems to analysed in order to investigate the effect of each factor. An be 785C. With reference to the soaking time, 30 min and examination grid was constructed, i.e. an arithmetic mean I h lead to the best results in terms of shrinkage; therefore, a vas calculated on all values obtained in different processing thermal treatment of 30 min was selected in order to treatment where a factor had a specific value. The results are minimize the processing time. Higher pressure seems to plotted in Fig 3 for the shrinkage and the relative density, give a greater shrinkage. No significant conclusion can be respectively. For example, the value for diameter shrinkage drawn out in terms of volume fraction of reinforcement of Fig 3a corresponding to 685C was obtained making an As regards the relative density, it should be noted that the average on all diameter shrinkage output values obtained in values were determined both with helium picnometer and FACTORS EFFECT 20900 08900890 0897089708930895 F075 6857895985301h2h28MPa42MPa56MPa10%20%30% FACTORS I Fig 3 Layout of the effect of the different factors on:(a)the shrinkage:()diameter;()thickness and(b) the relative density4. Results and discussion Fig. 2(a–c) illustrates the results obtained for each processing treatment in terms of diameter and thickness shrinkage, and relative density (percentage of the theoretical value). These results show that treatments 7, 8 and 9 are unacceptable since the sample present an expansion in thickness. Each output parameter, namely the diameter and thickness shrinkage and relative density, were separately analysed in order to investigate the effect of each factor. An examination grid was constructed, i.e. an arithmetic mean was calculated on all values obtained in different processing treatment where a factor had a specific value. The results are plotted in Fig. 3 for the shrinkage and the relative density, respectively. For example, the value for diameter shrinkage of Fig. 3a corresponding to 685 8C was obtained making an average on all diameter shrinkage output values obtained in those treatments where the soaking temperature was 685 8C, namely treatments 1, 2 and 3. As regards the shrinkage, the effect of temperature, soaking time, pressure and reinforcement volume fraction can be evaluated. In particular, as previously observed, the temperature of 885 8C leads to an expansion in thickness; in fact, such temperature coincides with the temperature of half-ball [16] of the frit used. In this condition, the viscosity becomes too low and spherical pores arise. The most suitable temperature for composites densification seems to be 785 8C. With reference to the soaking time, 30 min and 1 h lead to the best results in terms of shrinkage; therefore, a thermal treatment of 30 min was selected in order to minimize the processing time. Higher pressure seems to give a greater shrinkage. No significant conclusion can be drawn out in terms of volume fraction of reinforcement. As regards the relative density, it should be noted that the values were determined both with helium picnometer and Fig. 3. Layout of the effect of the different factors on: (a) the shrinkage: (C) diameter; (&) thickness and (b) the relative density. V. Cannillo et al. / Composites: Part A 37 (2006) 23–30 27