140 5 Materials for Lightweight Structures,Civil Infrastructure,Joining and Repair case of the welding of metals.Although a thermoplastic material softens at the glass transition temperature,it needs to be heated to temperatures close to or beyond the melting temperature in order for it to be sufficiently fluid for a strong bond to form.The required temperature depends on the pressure used to hold the adjoining surfaces together during the joining operation.The higher the pressure, the lower is the required minimum temperature. Polyphenylene sulfide(PPS)is a high-temperature thermoplastic polymer with a thermosetting/thermoplastic character.Its melting temperature is 280C and its glass transition temperature is 90C in the material used to obtain the results given below.Due to the CTE mismatch between crossply laminae of carbon fiber PPS-matrix composite,thermal stress arises during cooling after the bonding has been conducted at an elevated temperature.As a result,debonding can take place during cooling.This debonding can be monitored in real time by measuring the contact electrical resistance of the bonding interface.Upon debonding,the resis- tance increases abruptly.Figure 5.10 shows the effect of the bonding temperature on the bond between(PPS)surfaces,with the pressure fixed at 4.8 x 103Pa during the bonding and subsequent cooling.The heating rate up to the bonding temper- ature is 10C/min and the temperature is held at the bonding temperature for 5h. When the bonding temperature is 260,280,or 285C(i.e.,below the melting tem- perature,at the melting temperature,or just 5C above the melting temperature), debonding occurs during the cooling,so that the bonding process fails.However, when the bonding temperature is 290C(i.e.,10C above the melting temperature), 400 300 150 300 350 300 100 250 200 200 50 150 150 100 100 0 15 防 -100 10 15 20 Time (h) b Time(h) 300 300 300 250 250 200 200 20 200 100 150 150 100 100 50 50 分 250 -100 15 0 15 20 Time (h) d Time(h) Figure 5.10.Effect of PPS-PPS bonding temperature on the variation in contact electrical resistance at a constant pressure of4.8×103Pa.a260℃：b280℃c285℃d290℃.(From[3)140 5 Materials for Lightweight Structures, Civil Infrastructure, Joining and Repair case of the welding of metals. Although a thermoplastic material softens at the glass transition temperature, it needs to be heated to temperatures close to or beyond the melting temperature in order for it to be sufficiently fluid for a strong bond to form. The required temperature depends on the pressure used to hold the adjoining surfaces together during the joining operation. The higher the pressure, the lower is the required minimum temperature. Polyphenylene sulfide (PPS) is a high-temperature thermoplastic polymer with a thermosetting/thermoplastic character. Its melting temperature is 280°C and its glass transition temperature is 90°C in the material used to obtain the results given below. Due to the CTE mismatch between crossply laminae of carbon fiber PPS-matrix composite, thermal stress arises during cooling after the bonding has been conducted at an elevated temperature. As a result, debonding can take place during cooling. This debonding can be monitored in real time by measuring the contact electrical resistance of the bonding interface. Upon debonding, the resis￾tance increases abruptly. Figure 5.10 shows the effect of the bonding temperature on the bond between (PPS) surfaces, with the pressure fixed at 4.8 × 103 Pa during the bonding and subsequent cooling. The heating rate up to the bonding temper￾ature is 10°C/min and the temperature is held at the bonding temperature for 5h. When the bonding temperature is 260, 280, or 285°C (i.e., below the melting tem￾perature, at the melting temperature, or just 5°C above the melting temperature), debonding occurs during the cooling, so that the bonding process fails. However, when the bonding temperature is 290°C (i.e., 10°C above the melting temperature), Figure 5.10. Effect of PPS–PPS bonding temperature on the variation in contact electrical resistance at a constant pressure of 4.8 × 103 Pa. a 260°C; b 280°C; c 285°C; d 290°C. (From [3])