Residual stresses in fibre reinforced composites can give rise to a number of undesired effects such as loss of dimensional stability and premature fracture. Hence, there is significant merit in developing processing techniques to mitigate the development of residual stresses. However, tracking and quantifying the development of these fabrication-induced stresses in real-time using conventional non-destructive techniques is not straightforward. This article reports on the design and evaluation of a technique for manufacturing pre-stressed composite panels from unidirectional E-glass/epoxy prepregs. Here, the magnitude of the applied pre-stress was monitored using an integrated load-cell. The pre-stressing rig was based on a flat-bed design which enabled autoclave-based processing. A method was developed to end-tab the laminated prepregs prior to pre-stressing. The development of process-induced residual strain was monitored in-situ using embedded optical fibre sensors. Surface-mounted electrical resistance strain gauges were used to measure the strain when the composite was unloaded from the pre-stressing rig at room temperature. Four pre-stress levels were applied prior to processing the laminated preforms in an autoclave. The results showed that the application of a pre-stress of 108 MPa to a unidirectional [0]16 E-glass/913 epoxy preform, reduced the residual strain in the composite from −600 µε (conventional processing without pre-stress) to approximately zero. A good correlation was observed between the data obtained from the surface-mounted electrical resistance strain gauge and the embedded optical fibre sensors. In addition to “neutralising” the residual stresses, superior axial orientation of the reinforcement can be obtained from pre-stressed composites. A subsequent publication will highlight the consequences of pres-stressing on fibre alignment, the tensile, flexural, compressive and fatigue performance of unidirectional E-glass composites.

Polydimethylsiloxane (PDMS) colloidal silica composites prepared with the use of the dispersion of colloidal silica (CS) of similar particle size and distribution in different mediums/solvents are investigated for their rheological, thermal, and mechanical properties. Regardless of the dispersion medium of CS, thermal analysis showed the increased thermal stability of PDMS with the addition of CS. The rheological analysis showed that the composites prepared from CS dispersed in isopropanol (IPA) and CS dispersed in methylethylketone (MEK) showed significant enhancement in viscosity at higher loadings as compare with the composite prepared from the CS dispersed in water and methanol indicating more Filler-polymer interactions. Similarly, the tensile stressstrain curves, hardness, and tear strength displayed significant improvement with PDMS-CS-MEK and PDMS-CS-IPA composites. The results of this study not only provide the insights of solid-liquid-liquid interface leading to different extent of polymer-filler interaction, there by the bulk properties, it also helps to minimize the surface treatment steps while preparing the composites. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125: E515-E522, 2012