37 Dynamic thermal stress

Diamond has a low heat capacity, a low thermal expansion coefficient, and a high mechanical and thermal stability. These properties are very useful for devices using high dynamic thermal stress such as ink-jet heads. Indeed, ink-jet heads were fabricated using diamond films [17, 422]. Figure 13.8 shows a thermal actuator... 

Mechanical Failures Cracks or debonding of the catalyst from the substrate material can occur from thermal stresses as well as dynamic forces on the modules. The catalyst must be carefully handled to prevent premature fracturing. Each requires a warm-up and cool-down rate. 

The four key features of PTR-MS can be summarised as follows. First, it is fast. Time dependent variations of headspace profiles can be monitored with a time resolution of better than 1 s. Second, the volatile compounds do not experience any work-up or thermal stress, and very little fragmentation is induced by the ionisation step hence, measured mass spectral profiles closely reflect genuine headspace distributions. Third, measured mass spectral intensities can be directly related to absolute headspace concentrations, without calibration or use of standards. Finally, it is not invasive and the process under investigation is not affected by the measurements. All these features make PTR-MS a particularly suitable method to investigate fast dynamic process. 

The current method of determining the energy properties of polyurethane is the Dynamic Thermal Mechanical Analyzer (DTMA). This instrument applies a cyclic stress/strain to a sample of polyurethane in a tension, compression, or twisting mode. The frequency of application can be adjusted. The sample is maintained in a temperature-controlled environment. The temperature is ramped up over the desired temperature range. The storage modulus of the polyurethane can be determined over the whole range of temperatures. Another important property closely related to the resilience, namely tan delta (8), can also be obtained. Tan (8) is defined in the simplest terms as the viscous modulus divided by the elastic modulus. 

Stress relaxation, thermal expansion, dynamic methods Stress relaxation, Young s modulus, dynamic methods... 

The two examples, deliberately chosen for their simplicity, show that computational fluid dynamics facilitate a more in-depth examination of the local flow behavior of twin screw extruders. Local peaks in the mechanical and thermal stresses can be easily identified. By changing the geometry, stresses can be reduced and the quality of the polymer can thereby be optimized. Another application focus is the rapid determination of the dimensionless axis intercepts for the pressure build-up A, and A2 and for the power requirement B, and B2. The significance of these parameters has already been discussed in detail in the two previous chapters. 

First, there is a metal shell, generally made of carbon steel, which must provide a rigid leakproof elastic casing to support the ceramic lining, the possible stresses resulting from its growth, thermal stresses, the contents of the vessel and other static and dynamic loadings that will be imposed upon the vessel when it is placed in service. 

Model investigation of ceramic-metal FGMs under dynamic thermal loading Residual stress effect, thermal-mechanical coupling effect and materials hardening model effect... 

Dynamic mechanical thermal analysis, a non-sample-destructive technique in which an oscillatory stress is applied to the sample and the resultant strain determined as a function of both frequency and temperature. Examples of this technique include thermal-ramped oscillatory rheometry and conventional dynamic thermal mechanical analysis. 

The finite element (FE) model of the FSSW process was done using ABAQUS/Explicit software. A 3-D dynamic fully coupled thermal-stress analysis was performed to obtain thermomechanical responses of the FSSW process. Two features in the FE package were deployed in order to obtain the results ... 

In summary, the addition of the dynamic, thermal and fatigue effects of a natural convection cooldown on the System 80+ reactor vessel does not result in the vessel stresses or fatigue usage factor exceeding the allowable limits specified in the ASME B PV Code, Section III. Therefore, this issue is resolved for the System 80+ Standard Design. 

Possible reasons for the final rapid failure of the vessel may be structural instability of the vessel, rapid overpressurization due to a dynamic head space impact of the two-phase swell initiated upon a depressurization (initiated by the formation of a thermal crack or tear which arrests), or the rapid quenching of its crack tip, due to the two-phase discharge, that results in large local thermal stresses that cause the uncontrolled vessel failure. 

Whether the vessel fails completely as a result of severe quenching of the superheated vapor-space metal, the imposed thermal stresses or the dynamics, i.e., the water-hammer like impact of the swell upon the already damaged shell and its fracture mechanic criticality, the time scales for the two-step processes envisaged could range from the near zero to tens of milliseconds (for an immediate quenching case) to the ten of seconds (for the mist-flow cooling case). Indeed, two-step failures have been noted previously but not explained (e.g., Birk and Cunningham, 1996). 

Equipment support legs should be braced unless their dimensions warrant departure from this recommended practice. Resonance should be avoided and, in some cases (e.g. for core internals for which it is difficult to avoid resonance by means of modifying the design), the vibration characteristics of the reactor building s internal structure itself may be modified to prevent resonance effects. If systems are made stiffer, the effects of thermal stresses, other dynamic loads and differential motions of the supporting points should be considered. 

DMA provides material scientists and engineers with the information necessary to predict the performance of a material over a wide range of conditions. Test variables include temperature, time, stress, strain, and deformation frequency. Because of the rapid growth in the use of engineering plastics and the need to monitor their performance and consistency, dynamic thermal analysis has become the fastest growing thermal analysis technique. 

Equation (5.61) shows that the voltage loss rp (or mean current, which is proportional to rp) increases the slope of T x). This effect has been reported in numerical calculations (Inui et al., 2006). One of the consequences of this effect is that the thermal stress due to dynamic variation of load is maximal at the air channel outlet. 

A problem of the reduction in scale of the production to the miniplant scale developed in the simulation of the discharge of steam, since the volume and the cross-section area change by different orders of magnitude. This means it is not possible to keep both steam load and steam introduction duration constant during the reduction in scale from production to the miniplant. An elegant solution is to carry out separate experiments regarding the influence of thermal stress duration and the influence of fluid dynamic load. 

During a temperature cycle, emulsion stability can be evaluated using dynamic mechanical analysis (DMA) by means of viscosity measurements. Here, the sample is exposed to a small shear deformation with fixed amplitude and frequency and the complex dynamic shear modulus G = G - - G" is determined. G characterizes the elastic properties and G" the viscous properties of the material. A change in the modulus from cycle to cycle indicates structural changes induced by the applied thermal stresses [12,13]. 

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