Load stepping test

Figure 3-106. A load-stepping test to detennine the limiting PV capability of a bearing material.

At each velocity a load-stepping test is conducted. The friction torque and bearing temperature, which are plotted continuously, are allowed to reach equilibrium at each loading (see Fig. 3-106) [323]. The equilibrium condition is maintained for about 30 min., at which point the load is increased. At an advance load increment the friction torque and temperature will not stabilize. The slope of the curve will increase sharply in the friction torque or temperature plot. An increase in temperature or torque will eventually result in bearing failure. The pressure limits at several velocities provide a curve showing the limiting PV capability of the bearing material [323]. 

Figure 9-4 Too Little Phase Margin Shows Up in a Step-Load Response Test...

Forbes and Silver [40] published data directly comparing the alkyl ester tri-n-butyl phosphate and the aryl ester tricresyl phosphate. Table 11-13 shows the details of this comparison as well as wear data for the acid ester di-n-butyl phosphate. The wear/load index and the initial seizure load show substantially no discrimination between tributyl phosphate and tricresyl phosphate and very little advantage of the compounded oil over the base oil. The low-load wear test distinctly shows better performance with tricresyl phosphate. The data for di-n-butyl phosphate are at variance with the hypothesis that hydrolytic degradation to the acid ester is the first step in the antiwear action of neutral phosphate esters. On the other hand, Bieber, Klaus and Tewksbury [41] separated acidic constituents from commercial tricresyl phosphate by preparative chromatography, and on blending these constituents back into the original tricresyl phosphate at various concentrations they observed enhancement of antiwear action in the four-ball test, as shown in Fig. 11-7. It should be noted that Bieber et at. worked with only 0.051% phosphorus in the lubricant, which may explain the sensitivity they observed to acid impurities. 

Figure 14-10. Genesis of scuffing on the rubbing face of a gear tooth, (a) view of regions rubbed at three progressively increased load steps in the Ryder test. (b) Shows the orientation of the imprint of the narrow tooth on the wide tooth of the test gear set.

The hydraulic actuator, driven by a function generator, automatically produced pure tension stress cycles in the test ring, each with a period of 20 sec. After every 100 cycles, the actuator was controlled with manual input for one cycle to allow pauses at intermediate load steps. At each such step, the strain gauges were scanned by a 30-channel Vishay/Ellis data recording system, and the copper... 

The long-term strength behaviour test is carried out in the same way as the short-term strength test, namely in single-axis strip tests parallel to the threads (see the tests at 23°C on page 138). Load steps should be set at 10%, 20%, 50% and 90% of the short-time tensile strength. Ten samples are required to be tested for each load step. After 1000 hours the residual strength is established. 

The strength in long-term behaviour is established exactly as for short-term strength in single-axis tests parallel to the threads. The following loading steps are used ... 

Ten samples are tested for each load step. After 1000 hours the residual strength is then established. Pre-stress and working stress are defined above with respect to the strength. 

A schematic representation of a creep experiment is given in Fig. 13.11. Similar to enthalpic relaxation measurements, in a creep test the sample is quenched from above Tg to the annealing temperature T. A series of short (typically less than 10 % of the aging time ta) load-unload tests are performed. As shown in Fig. 13.11, the applied stress, a, is constant and the time-dependent response, the strain, is measured following both load and unload steps. Because times fe during which creep response is measured are kept deliberately short, the creep response gives a snapshot of the viscoelastic properties of the material at a particular aging time. 

The tests were conducted in different load steps. The corresponding EW-PGA values measured directly at the foundation were 0.074g, 0.150g and 0.524g,... 

The step-modified slow strain-rate or Rising Step-Load (RSL ) test produces an increasing stress intensity that is different at each step-load but remains constant with crack extension for a Chaipy-sized SE(B) four-point bend specimen while each load level is maintained constant for a period of time. The rising step-load test was developed as an accelerated low-cost test for measuring the resistance of steels and weldments to IHE or EHE [45,46 ]. The load is constantly increased under displacement control, but incrementally in steps with each step being sustained for a period of time so that the onset of subcritical crack extension can be detected, which is the threshold for the onset of IHE or EHE. The RSL test differs from the SSRTT, which measures the differences in ductility parameters over the... 

This step involves generating the photoplottmg files, pick-and-place files, bare and loaded board test files, drawings, and bills of material needed to do the actual manufacturing.Typical lists of these files are shown in Tables 14.1 and 14.2. 

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