Loading velocity

Earlier work had shown that lower-molecular weight compatibilizers have a more significant effect on reducing the ductile-brittle transition than higher-molecular weight ones. Eurther, the brittle-ductile temperature. I m, increases with the increase in loading velocity. 

In practice, rubbers do not normally obey these rules and the coefficient is a variable constant, its value depending on the real contact area, normal load, velocity and other factors. In fact, friction is sensitive to just about... 

Plastisol properties depend on a number of factors, the most important among which are the nature of the polymer (PVC), the identity of plasticizer and other additives, the composition of formulations, the conditions of preparation and storage, the load-velocity (first of all, stress and shear rate), and temperature conditions of processing. Depending on these parameters, the character of plastisol flow may vary widely. That is why, in spite of a number of papers devoted to the study of the rheological (viscous) properties of plastisols (e.g. 2,5 37,38)), these still can not be considered as well studied and widely accepted. 

Load type and rate of loading, velocity/duration of test ... 

Figure 2. "Wear as a function of 0 and tan 0 for the experiment shown in Figure 1. Load IN sliding velocity ca. 4 x 10 5 ms l no lubrication temperature ca. 20°C. The wear is calculated from, w, the scratch width. Open symbols PMMA and closed symbols PTFE. These cutting angles are functions of load, velocity and the state of lubrication.

Fig. 4.1. Wear rate of steel with 0.52% carbon content depending on loading. Velocity - 0.1 m/s [10]...

The nature of the metal counterhody significantly influences the wear of contacting polymers (Table 4.11). Under low loads and friction velocities tribological characteristics of metal-polymer friction pairs depend only slightly on the metal nature. As soon as the load-velocity regime becomes more severe, the role of this factor increses drastically [108]. 

Co-Cr-Mo + UHMWPE 0.04-0.06 Hip joint simulator Load 2.5 kN static load Velocity 30 cycles/min Duration 1.8 million cycles Lub serum Weightman et al. (1973)... 

Co-Cr-Mo + UHMWPE (Duo-Patella) 1.8 mg/10 cycles NA Knee joint simulator 700 lb peak load Velocity = 33 cycles/min Duration 10 cycles Lub double spun bovine serum Creep and fatigue cracks evident. Rose et al (1984)... 

Subsequently the statically stressed specimens were claimed within a dynamic four-point-bending test with a load velocity of 1,000 MPa/s till fracture to determine the residual strength. Because of the local damage It Is assumed that the residual material strength Is reduced increasingly with an increasing number of fretting cycles. 

CETR 2 tribometer (Center for Tribology, Inc., Campbell, CA, USA) was used to run the tests using a ball-on-disk geometry. This tribometer allows the independent programming of normal load, velocity, radius and duration. Prior to the actual tests, running-rn of the ball was performed at 5 N load with a speed of 31.4 mm/ min for 2h, outside the region to be used for XPS analysis and in the presence of the test lubricant. The running-in was performed in order to create a at spot on the bottom of the ball. This at spot was then placed in contact with the surfaee for the subsequent runs and de ned the apparent eontaet area. 

The fibrillar structure of the crazes is t5 ical of PS. Another glassy polymer is styrene-acrylonitrile (SAN) copolymer with a PS content of usually about 74%. In this material the dominant deformation structures are homogeneously deformed zones, but in many cases they coexist with the fibrillated crazes (2,29). Depending on the loading conditions (stress state, loading velocity, temperature), the deformation character can be shifted from one to another. Another typical glassy polymer is PMMA with a t5 ical appearance of homogeneously deformed crazes at room temperature (29). 

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