In situ consolidation

Techniques commonly used to manufacture advanced composites from prepregs, which are available in unidirectional fiber or fabric form, include compression molding, vacuum-bag autoclave molding, stamp molding, thermoforming, and on-line (in situ) consolidation [3]. In compression and vacuum-bag autoclave molding techniques, the prepreg is cut to the dimensions of the structure, and the fiber directions are oriented to obtain the required... 

In the in situ consolidation model of Liu [26], the Lee-Springer intimate contact model was modified to account for the effects of shear rate-dependent viscosity of the non-Newtonian matrix resin and included a contact model to estimate the size of the contact area between the roller and the composite. The authors also considered lateral expansion of the composite tow, which can lead to gaps and/or laps between adjacent tows. For constant temperature and loading conditions, their analysis can be integrated exactly to give the expression developed by Wang and Gutowski [27]. In fact, the expression for lateral expansion was used to fit tow compression data to determine the temperature dependent non-Newtonian viscosity and the power law exponent of the fiber-matrix mixture. 

Liu, K.S., Ph.D. Thesis, A Mathematical Model for In-Situ Consolidation of Thermoplastic Composites, (1995) Stanford University, Stanford, CA... 

Figure 13.4 Hot gas torch for in situ consolidation of thermoplastic matrix cylinders equipment (courtesy of Engineering Technology, Inc., ENTEC )...

A theoretical model for intimate contact for in-situ consolidation has been developed in Reference 21. In this model, the irregular surface of the thermoplastic tow is modeled as a series of rectangular elements, oriented along the fiber axis, which are deformed as local pressure is applied (Fig. 13.11). The amount of flattening is quantified as the degree of intimate contact Dic (Eq. 13.14)... 

In fiber placement, a moving head is mounted to a multidegree of fieedom carriage. The fiber placement head is designed to cut and place each tow individually. The head may also include a controlled heat source and compaction roller for in situ consolidation. Tow placement with in situ consolidation has made it possible to place preimpregnated tape along nongeodesic paths, manufacture parts with concave sections, and to locate ply dropoffs precisely. 

The combination of materials with different rheological, thermal and mechanical properties requires the study of phenomena related to multimaterial structiues, such as optimization of in-situ consolidation and... 

Key words in situ consolidation, impregnation, main heater, thermoplastic filament winding. 

Nicodeau, C., Cinquin, J., Regnier, G. and Veidu, J., In situ consolidation process optimization for thermoplastic matrix composites . Proceedings of International SAMPE Symposium, Long Beach, CA, USA, April-May, SAMPE, Paper 212, 2006. 

Schledjewski, R., Thermoplastic tape placement process - in situ consolidation is reachable . Plastics, Rubber and Composites, 2009, 38(38), 379. 

Schledjewski, R. and Schlarb, A. K., In situ consolidation of thermoplastic tape material - Effects of tape quality on resulting part properties . Baltimore, Proceedings of Sampe 2007, USA, 2007. 

Khan, M. A., Mitschang, P. and Schledjewski, R., Tracing the void content development and identification of its effecting parameters during in situ consolidation of thermoplastic tape material . Polymers and Polymer Composites, 2010, 18(1), 1. 

Other methods such as ultrasonic heating, microwaves, induction heating, or high frequency radiation and furnace heating are of no industrial importance or lead to inferior material properties [28,43-46]. The thermoplastic filament winding process is called in situ consolidation and is schematically shown in Figure 1.11. With such devices, it is possible to process tapes of different widths with winding speeds up to 30 m/min. However, better material properties are derived at speeds of between 6 and 12 m/min [30]. 

Grain size of Fe-Cr alloys (used for the investigation of the effect of nanocrystalline structure on oxidation resistance) was limited to 54 ( 4) nm which could be further decreased with the recent advancements in the sample preparation techniques such as one recently developed by Gupta et al [122] where an artefact free FeCrNi alloy with a grain size less than 10 nm was produced by in-situ consolidation technique. Further investigations on such alloys with grain size below 10 nm will demonstrate pronounced effect of triple points and grain boundaries and it may be possible to develop stainless steels with further improved oxidation resistance but less Cr content. 

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