Thermal Spiking Effects

Thermal spiking induces microcracking in composites it is enhanced by the presence of moisture. In turn, this damage increases the moisture absorption capacity of composite lay-ups, typically by 100%. This phenomenon is of some concern in aerospace applications, where rapid temperature variations may occur during flight. 

A review of earlier works on this matter was given by Hahn (1987). Some specific data are given by several authors (e.g. CoUings and Stone 1985). 

Aiello MA, Leone M, Aniskevich AN, Starkova OA (2006) Moisture effects on elastic and viscoelastic properties of CFRP rebars and vinylester binder. J Mater Civ Eng 18(5) 686-691 

Althof W (1979) The diffiisirai of water vapour in humid air into the htnidlmes of adhesive bonded metal joints. Proceedings of the 11th National SAMPE Conference, vol 11, SAMPE, Azusa, November 1979, pp 309-332 

Apicella A, Migliaresi C, Nicolais L, laccarino L, Roccotelli S (1983) The water ageing of unsaturated polyesto-based composites influence of resin chemical structure. Cranposites 14(4) 387-392 

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In early theories of the chemical effect of radiation it was supposed that the changes one observes in an irradiated medium are due to formation of local heated regions, which subsequently became known as thermal spikes. Later it was shown that for a particle with low LET the heating is neither considerable nor is sufficiently long to have an essential effect on chemical transformations. For instance, according to estimates made by Mozumder,23 the rise of the temperature inside a spur is only about 30 K, while the time r1/2 by which the temperature in the center of the spur lowers to a half of its initial value is about 6 x 10 12 s. 

For the c-BN formation a stress threshold was observed in the deposited layers. The h-BN intermediate layer shows a preferred orientation, where the c-axis of the h-BN is parallel to the substrate. Both effects are explained by the compressive biaxial stress induced by the ion bombardment. The mechanism for the conversion of h-BN into c-BN is explained by rather high temperatures originated during thermal spikes (direct h-BN —> c-BN transformation). The stress caused by the bombardment with high energetic ions is considered to be a reason for the growth of the c-BN crystals [190, 191]. A stress within the layer of up to 10 GPa has been observed. This biaxial stress causes a hydrostatic pressure up to the values usual in HP-HT synthesis. 

Although the effect of chemical bonding on energy dissipation in chemical systems is not included [54,55], the cylindrical thermal spike model takes into account the specific features of an ion-beam bombardment process such as energy loss and collision cascade. In particular, the individual ion bombardment will induce an initial energy deposited in a finite volume through collision cascades as illustrated in Figure 16.5. 

It should be stressed that miiltiphoton pump-probe studies are frequently carried out at high excitation density this may result in a bulk thermal spike that considerably changes both the electron thermahzation and geminate recombination dynamicsIt seems likely that irreproducible reports of imusual spectral features and exotic short-lived intermediates are traced to the effects of such thermal spikes. 

Figure 12.9 Illustration of the effect of thermal spiking to 140 °C on the moisture absorption of a Fibredux 927C unidirectional laminate in 96% RH at 50 °C. The individual points represent the actual moisture content immediately before and after a thermal spike. The continuous line is for the isothermal control under identical humid conditions.

Figure 3.5 Effect of thermal spiking to 140°C on the moisture absorption of Fibredux 924C-Og laminate, at 50°C and 96% RH. The moisture content immediately before and after 140°C spiking ( ) isothermal control data (50°C) ( ), [11]...

Table 3.4 Effect of thermal spiking and moisture conditioning at 96% RH and 50°C on the primary (T.i) and secondary (t 2) tan 8 peaks for advanced epoxy resin systems [22]... 

Figure 3.8 Effect of moisture absorption at 50°C, 96% RH and thermal spiking on the temperature for the onset of the relaxation region within the glassy polymer, as defined by reduction in storage modulus 924C (V) 927C ( ) 5245C ( ) [22]...

K E Stansfield, The Effects of Stress and Thermal Spiking on the Hygrothermal Response of Carbon Fibre Reinforced Plastics, PhD Thesis, Kingston Polytechnic, 1989. 

T A Collings and DEW Stone, Hygrothermal Effects in CFC Laminates. Parti-Damaging Effects of Temperature, Moisture and Thermal Spiking, Royal Aircraft Establishment Technical Report 84003, Famborough, January 1984. 

Collings T, Copley S (1983) On the accelerated ageing of CFRP. Composites 14(3) 180-188 Collings T, Stone D (1985) Hygrothermal effects in CFC laminates damaging effects of temperature, moisture and thermal spiking. Compos Struct 3(3-4) 341-378 Davies P, Choqueuse D, Mazeas F (1998) Composites underwater. In Reifsnider KL, Dillard DA, Cardon AH (eds) Progress in durability analysis of composite systems. Balkema, Rotterdam, pp 19-24... 

Although it is now commonly conjectnred that a local thermal equilibrium does not effectively describe the ionization/nentralization process/es active in atomic secondary ion formation/snrvival, the possibility of relating modified variations of the LTE concept to the trends resnlting from thermal spike-type processes (see Section 3.2.1.2) has also since been proposed. Likewise, LTE-based arguments have attracted interest in modeling-specific molecular secondary ion yields (see Section 3.3.4). 

Cooling effects (> 10 to < 10 sec) - e.g. thermal spikes along collision cascades. 

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