Curing stress effect

Figure 5. Curing schedule effect on zero stress temperature.

In conclusion, the picture of an interphase surrounding a filler particle, whether induced by adsorption, by other phenomena such as thermal stresses, or by some combination of these, can help explain specific effects of filler-matrix interactions on behavior. However, the interphase itself may well not be well defined and monolithic, so that a gradation in properties is probably more realistic (Kaufman et al, 1971 Morgan, 1973). In addition, more than one component (e.g., both densified and rarefied) may coexist. Further studies of adsorption per se, the chemistry of cured matrix resins at interfaces, relaxation behavior, and thermal stress effects should be of great value. 

Kriz RD, Stinchcomb WW (1982) Effects of moisture, residual thermal curing stresses, and mechanical load on the damage development in quasi-isotropic laminates. In Reifsnider KL (ed) Damage in composite materials, ASTM STP 775. American Society for Testing and Materials, Philadelphia, pp 63-80... 

The design and analysis of composite structures relies on experimental data. Testing of composites serves a variety of purposes such as the characterization of constituent materials i.e. the fiber, matrix and fiber/matrix interface, verification of the micromechanics analysis including the effects of curing stresses, temperature and moisture, as well as life prediction through accelerated testing[l]. 

Microstructure. Whereas the predominate stmcture of polychloroprene is the head to tail /n7 j -l,4-chloroprene unit (1), other stmctural units (2,3,4) are also present. The effects of these various stmctural units on the chemical and physical properties of the polymer have been determined. The high concentration of stmcture (1) is responsible for crystallization of polychloroprene and for the abiUty of the material to crystallize under stress. Stmcture (3) is quite important in providing a cure site for vulcanization, but on the other hand reduces the thermal stabiUty of the polymer. Stmctures (3),(4), and especially (2) limit crystallization of the polymer. 

The importance of the nature of the catalyst on the hardening reaction must also be stressed. Strong acids will sufficiently catalyse a resol to cure thin films at room temperature, but as the pH rises there will be a reduction in activity which passes through a minimum at about pH 7. Under alkaline conditions the rate of reaction is related to the type of catalyst and to its concentration. The effect of pH value on the gelling time of a casting resin (phenol-formaldehyde ratio 1 2.25) is shown in Figure 23.15. 

In addition to the considerable difference of the properties of the cured resins with different hardeners it must also be stressed that the time and temperatures of cure will also have an important effect on properties. As a very general rule, with increasing aliphatic amines and their adducts the time of cure and temperature of cure (up to 120°C at least) will improve most properties . ... 

Of course, the role of the artificially introduced stochastics for mimicking the effect of all eddies in a RANS-based particle tracking is much more pronounced than that for mimicking the effect of just the SGS eddies in a LES-based tracking procedure. In addition, the random variations may suffer from lacking the spatial or temporal correlations the turbulent fluctuations exhibit in real life. In RANS-based simulations, these correlations are not contained in the steady spatial distributions of k and e and (if applicable) the Reynolds stresses from which a typical turbulent time scale such as k/s may be derived. One may try and cure the problem of missing the temporal coherence in the velocity fluctuations by picking a new random value for the fluid s velocity only after a certain period of time has lapsed. 

To determine the effect of the curing schedule upon the thermal stress development, a 0% excess MDA sample was made by first B-stage curing (2 hrs at 80°C) the sample, cutting it into the beam dimensions and then placing it in the apparatus. The deflection of the beam was measured during the remainder of the curing schedule (2 hrs at 150°C and 2 hrs at 180°C). 

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