126 High Performance Thermoplastic Resins and Their Composites bolted joint performance to the epoxy composite.As shown in Figure 57.PEEK composites exhibited 10-15%higher bearing strength than the epoxy composites for both quasi-isotropic and0°/9o°laminates. 6.3 Adhesive Bonding Adhesive bonding is accomplished by placing an adhesive between the two parts to bc joined (the adherends).The load distribution of bonded joints is more uniform than mechanical fastened ones.Basically,the process involves four steps:i)surface preparation.a critical operation which ensures a good wetting of the adhesive to the adherend,ii)placement of the appropriate adhesive,iii)application of heat and/or pressure and iv)curing of the adhesive [2361.Experimental studies [103,241]have shown that conventional structural adhesives technology used for thermoset composites may be inadequate for thermoplastic composites.Due to their relative chemical inertness,it may be difficult to adhesively bond some thermoplastic composites with several of the currently used adhesives [239,241]. Adhesives used to bond thermoset composites are mostly thermosets and very often they are epoxy based adhesives [2361.Although several epoxy adhesives have shown compatibility with some thermoplastic composites in bonding processes [104.2421.the usage of an epoxy adhesive to join high performance thermoplastic composites may compromise the high temperature properties of the part and its water resistance.Using a thermoplastic matrix as an adhesive to bond thermoplastic composites presents several advantages.Among these are i)short processing time,ii)good thermal stability.iii)improved solvent resistance,iv)retention of bond strength at elevated temperature.v)low moisture absorption and vi)long shelf life. Kodokian and Kinloch [241]found that PEEK resin was a more effective adhesive in joining APC-2 composites than epoxy based adhesive.A similar observation was made when joining a ceramic plate to a metal case;a higher bond strength was obtained with PEEK film adhesive than with an epoxy [2431. 6.4 Fusion Bonding (Welding) Fusion bonding is a joining technique restricted to thermoplastic based composites where two or more parts are joined together by fusion and consolidation of their common interfaces (2441.As in adhesive bonding.it provides a more uniform load distribution than mechanically fastened joints but no additional new material,such as an adhesive,is involved. The fusion bonding techniques are faster and more easily automated than mechanical fastening and adhesive bonding techniques.The design of a welded joint is simllar to an adhesively bonded joint,i.e.single-lap,step-lap.double-lap and scarf joints can be used. Fracture analysis of welded joints assumes the same failure criterla that is used for mechanical fastening and adhesive bonding [236].126 High Performance Thermoplastic Resins and Their Composites bolted joint performance to the epoxy composite. As shown in Figure 57. PEEK composites exhibited 10 - 15% higher bearing strength than the epoxy composites for both quasi-isotropic and 0”/90” laminates. 6.3 Adhesive Bonding Adhesive bonding is accomplished by placing an adhesive between the two parts to be joined (the adherends). The load distribution of bonded joints is more uniform than mechanical fastened ones. Basically, the process involves four steps: i) surface preparation, a critical operation which ensures a good wetting of the adhesive to the adherend. ii) placement of the appropriate adhesive, iii) application of heat and/or pressure and iv) curing of the adhesive [236). Experimental studies (103.241) have shown that conventional structural adhesives technology used for thermoset composites may be inadequate for thermoplastic composites. Due to their relative chemical inertness, it may be difficult to adhesively bond some thermoplastic composites with several of the currently used adhesives 1239, 24 11. Adhesives used to bond thermoset composites are mostly thermosets and very often they are epoxy based adhesives 1236). Although several epoxy adhesives have shown compatibility with some thermoplastic composites in bonding processes [104.242], the usage of an epoxy adhesive to join high performance thermoplastic composites may compromise the high temperature properties of the part and its water resistance. Using a thermoplastic matrix as an adhesive to bond thermoplastic composites presents several advantages. Among these are i) short processing time, ii) good thermal stability, iii) improved solvent resistance, iv) retention of bond strength at elevated temperature, v) low moisture absorption and vi) long shelf life. Kodokian and Kinloch [241) found that PEEK resin was a more effective adhesive in joining APC-2 composites than epoxy based adhesive. A similar observation was made when joining a ceramic plate to a metal case; a higher bond strength was obtained with PEEK ffirn adhesive than with an epoxy [243]. 6.4 Fusion Bonding (WeldingI Fusion bonding is a joining technique restricted to thermoplastic based composites where two or more parts are joined together by fusion and consolidation of their common interfaces 12441. As in adhesive bonding, it provides a more uniform load distribution than mechanically fastened joints but no additional new material, such as an adhesive, is involved. The fusion bonding techniques are faster and more easily automated than mechanical fastening and adhesive bonding techniques. The design of a welded joint is similar to an adhesively bonded joint, i.e. single-lap, step-lap, double-lap and scarfjoints can be used. Fracture analysis of welded joints assumes the same failure criteria that is used for mechanical fastening and adhesive bonding 12361