Thermally and Pressure-Induced Stresses

Zheng, R. Kennedy, P. Phan-Thien, N. Fan, X.J. Thermoviscoelastic simulation of thermally and pressure induced stresses in injection molding. J. Non-Newtonian Fluid Mech. 1999, 84, 159-190. 

R. Zheng et. al., Thermo viscoelastic Simulation of Thermally and Pressure Induced Stresses in Injection Moulding for the Prediction of Shrinkage and Warpage for... 

Thermally and Pressure-Induced Stresses 6.3.1 Stress Development... 

Fig. 6.4 Thermally and pressure-induced stress (

In the calculation of the thermally and pressure-induced stresses, the material behavior can be described by either a viscous-elastic model (see, for example, Titomanlio et al. 1987 Jansen 1994 Boitout et al. 1995) or a viscoelastic model... 

For thin-walled injection-molded parts, the calculation of thermally and pressure-induced stresses can be simplified considerably by using the thin-film approximation. This enables us to apply the following assumptions ... 

Here the single term cr°. replaces (4 Cyki ) in Eq. 6.59. If Eq. 6.60 is to be used, the calculation procedure for the in-mold thermally and pressure-induced stress has to be continued to the room temperature. If the material has fully frozen... 

Total stresses applied on each lamina, k, are expressed as a summation of thermal, pressure, and launch induced stresses, as shown in Equation (1). The three stress components are assumed to be decoupled therefore, the total stresses are expressed as a linear combination of the three stresses. 

Figure 2. Thermal, pressure, and launch induced stresses of IM7/977-2 [0/90/90/0/0/90]s in fiber and transverse directions in the principal material coordinate at -253°C under various pressures.

The peak traction can now be obtained from the condition that at this site the PB domains will cavitate under the action of the negative pressures induced by the three principal stresses a , CT99, a , and the added negative pressure ct h. due to the thermal mismatch by reaching the cavitational strength of PB that we have estimated earlier to be 60 MPa at room temperature. Thus,... 

The heat weakens the tank shell around the ullage space. Thermally induced stresses are created in the tank shell near the vapor/Iiquid interface, and the heat-weakened tank plus the high internal pressure combine to cause a sudden, violent tank rupture. Fragments of the tank are propelled away from the tank at great force. Most of the remaining superheated liquid vaporizes rapidly due to the, pressure release. The rest is mechanically atomized to small drops due to the force of the explosion. A fireball is created by the burning vapor and liquid. 

The external case of the rocket motor supports the mechanically and thermally induced stresses, which are due to internal gas pressure, vibration, acceleration, thrust vector control, and differential thermal expansion of component materials. To accommodate these factors, the structural material should have high strength, adequate modulus, and resistance to buckling. Either a continuous glass filament wound epoxy plastic or a high temperature metal (steel, titanium, or aluminum) case serves as the exterior structural member. 

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