Load, intermittent

J)- Thermal curves for intermittent loads, the average heating not exceeding the permissible temperature rise Figure 3.16 Equivalent output of short-time duties... 

Describe any unusual load demand characteristics related to any output. These consist of intermittent loads such as motors, CR R, etc., and also any loads that may be removed from or added to the system as part of an overall system architecture, such as probes, handsets, and the like. 

Tests have shown that when total strain is plotted against the logarithm of the total creep time (ie NT or total experimental time minus the recovery time) there is a linear relationship. This straight line includes the strain at the end of the first creep period and thus one calculation, for say the 10th cycle allows the line to be drawn. The total creep strain under intermittent loading can then be estimated for any combinations of loading/unloading times. 

The effective increase in modulus due to intermittent loading is shown in Fig. 2.52. This illustrates that considerable material savings can be made if intermittent loading of the plastic can be ensured. 

All machines depend for their accuracy on the strength of their component parts, their bearings and on the type and efficiency of their lubrication systems. Many machine bearings are subjected to extremely heavy shock loads, or intermittent loads, or exposure to unfavorable environmental conditions, yet in spite of this they must always maintain their setting accuracy. 

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. 

Intermittent loading. The creep behavior of plastics that has been considered so far has assumed that the level of the applied stress will be constant. However, in service the material may be subjected to a complex pattern of loading and unloading cycles (Fig. 2-33). This variability can cause design... 

Fig. 2-34 Tensile creep and recovery during the intermittent loading.

Fig. 3-6 An example of intermittent loading involving successive creep strain and recovery.

The tensile data can be applied to the design of short-term (such as 1 or 2 hour duration) or intermittent loads in a product provided the use temperature, the humidity, and the speed of the load are within 10% of the test conditions outlined under the procedure. The intermittent specification merely indicates that there be sufficient time for strain recovery after the load has been removed. 

Creep is the long-term deformation of a polymer under a sustained or intermittent load at stresses below the yield point. We see creep at work when we place furniture on carpet. If we... 

Dynamic Loads Fatigue, Intermittent Load and Wear... 

Fatigue or dynamic fatigue can be defined as the decrease in load bearing capacity with time under cyclic or intermittent load, the term static fatigue being sometimes used to describe creep-rupture (see Sections 4.9.2 and 6.10). 

Hert, J., Liskova, M. and Landa, J. (1971) Reaction of bone to mechanical stimuli. Part I. Continuous and intermittent loading of tibia in rabbit. Folia Morphologia 19 290-300... 

Interrupted periodic operation with intermittent loading... 

The overall cell-stack efficiency (relative to the lower heating value for hydrogen) has been found to be typically around 40%, with a maximum of 45% around nominal current. These values are very low compared to the values in excess of 60% found for other cases like the HYSOLAR Electrolyser 2 at DLR. Operation of the DLR electrolyser with intermittent loads proved that ... 

Wolf A, Raiss RX, Steinmeyer J (2003) Fibronectin metabolism of cartilage explants in response to the frequency of intermittent loading. J Orthopaedic Res 21 1081-1089... 

Classification.—The classification and terminology for conveying and elevating equipment has grown quite confused and as conveyors are frequently installed at an inclination so that they elevate as well as convey, it is well to classify such material handling equipment as carries a continuous, or approximately so, load under the one head of conveyors and elevators, to distinguish them sharply from other material handling equipment which handle more intermittent loads. 

For instance, if there are high amp draws from motor start ups, etc., put a supercapacitor in parallel connection with a 12 volt rechargeable battery, and use this to supply those intermittent load needs adequately. To use a rechargeable battery alone, as mentioned, simply connect the output from the fuel cells to the battery and draw power from the battery. To use a supercapacitor and rechargeable battery, connect the battery and supercapacitor in parallel, connect the fuel cell output to these, and draw your power from the supercapacitor and battery connected leads. With these system additions you will need a diode so that reverse flow does not occur to the fuel cell stack, and fuse the circuit on both sides in case of shorts. A switch, either remote or direct, should be used to connect the power supply with any lines or equipment being powered. If you have AC power requirements you will need an inverter to convert DC to AC electricity. 

Performance. Carbon—zinc cells perform best under intermittent use and many standardized tests have been devised that are appropriate to such applications as light and heavy flashlight usage, radios, cassettes, and motors (toys). The most frequently used tests are American National Standards Institute (ANSI) tests (6). The tests are carried out at constant resistance and the results reported in minutes or hours of service. Figure 3 shows typical results under a light load for different size cells, whereas Figure 4 shows results for different types of R20 "D"-size cells under a heavy intermittent load. 

Compare with Miller and Brest [3] 1998 continuous plus intermittent loads 1200 W 2005 continuous plus intermittent loads estimated at 2800 W. 

Intermittent loading from overturning moment produced by winds... 

Determining the continuous current for a feeder to a switchboard or to its incoming transformer is a little more complicated. All the loads in a group need to be identified into continuous loads, intermittent loads and de-energised standby loads. 

The individual loads may be known to have diversity from their nameplate values. If this is the case then the diversity should be included in the estimation of the consumed power. The total load is estimated by adding together the continuous loads, a nominal proportion of the intermittent loads e.g. 30 to 50%, and a small proportion of the standby loads e.g. zero to 10%. The summation shonld be carried out in two parts, the first part for the active power and the second part for the reactive power. This is necessary because not all the loads in a group have the same power factor. Once these two totals are estimated the total volt-amperes can be found and then the cnrrent. 

Fatigue can be delined as the decrea.se in load-bearing capacity with time under load. Under constant load conditions this is termed static fatigue or creep rupture, and under cyclic or intermittent load dynamic fatigue. 

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