Intermittent stress application

Intermittent Stress Application during Irradiation. An experiment was carried out in which the beam remained on continuously, but the stress was applied remotely for only 12 seconds at the beginning of each minute. The data from the experiment are shown in Figure 7. 

Figure 7. Intermittent stress application during irradiation. Stress was applied for first 12 seconds of each minute during irradiation...

The data obtained here for intermittent stress application (Figure 8) on a polystyrene sample and the data of Mokulskii et al. (Figure 9) for creep of a PVC sample after various times of exposure to the nuclear radiation field can now be interpreted in terms of continued gas buildup within the samples during radiation exposure. This leads to the higher initial creep rates when stress is applied after the radiation beam has... 

In both mechanical and electrical testing, the frequency of dynamic stress application can be increased, although heating effects and time for relaxation processes have to be considered. For some products it is appropriate to simply use them more often, for example where in service the use is intermittent or there is normally downtime. 

Although this schedule is designed for infants, it is equally applicable to adults. The schedule is divided into two phases, an initial one during which the patient is adapting to the increasing glucose intake and a later one when he has achieved a more stable state metabolically. However, in the face of intermittent stress (i. ., surgery, infection, etc.), the schedule outlined under the initial period should be adopted since metabolic complications under these conditions are likely to be more frequent. 

Products that are subjected to a load have to be analyzed carefully with respect to the type and duration of the load, the temperature conditions under which the load will be active, and the stress created by the load. A load can be defined as continuous when it remains constant for a period of 2 to 6 hours, whereas an intermittent load could be considered of up to two hours duration and is followed by an equal time for stress recovery. The temperature factor requires greater attention than would be the case with metals. The useful range of temperatures for plastic applications is relatively low and is of a magnitude that in metals is viewed as negligible. 

Where exposure to the liquid in service is intermittent it may be of interest to know the effect on properties after drying. ISO 175 [16] includes procedures for measuring tensile stress, strain and hardness after a drying period in an oven. Depending on the application, measurements before or after drying may be required and possibly both will be of relevance. 

Property Summary Nylons are recommended for general-purpose gears and other mechanical components. Acetals for maximum fatigue life, for highly accurate parts, or exposure to extremely humid conditions. Phenolic-fabric laminates for low-cost, thin stamped gears or parts. Polycarbonates for intermittent, very high impacts (not recommended for applications involving repeated cyclical stress). TFE-filled acetals for heavy-duty applications. 

The application of tensile stresses to osteoblasts appears to cause induction of the BMP-4 gene in preosteoblastic cells and adjacent spindle-shaped fibroblasts suggesting that BMP-4 may play a pivotal role by acting as an autocrine and a paracrine factor for recruiting osteoblasts in tensile stress-induced osteogenesis. Intermittent hydrostatic pressure (IHC) up-regulates osteopontin (OPN) mRNA expression in osteoblast cell cultures. In both... 

In order for ER fluids to be used in various devices, it is necessary that (i) the induced shear stress be large (stress properties) (ii) the current density be small (current properties) (iii) when an electric field is continuously or intermittently applied the induced shear stress or current density does not change as a fimction of time (electrical permanence) (iv) viscosity without electric field application be small (flow properties) and (v) the stability of the suspended particles be high (suspension stability) [72]. 

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