As shown in Figure 1, the CLC fixture consists of two pairs of steel blocks, each pair clamped together with four bolts. During installation, the ends of the 5.5-inch-long specimen are flush with the ends of the blocks. The gripping surfaces of the steel blocks are 1.2 inches wide and are used to test specimens with a nominal width of 1 inch. As illustrated in Figure 2, these gripping surfaces are coated with tungsten carbide particles to enhance friction, thereby allowing higher shear loads to be transferred to the specimen. Moreover, since these surfaces are relatively smooth (100 grit), they do not damage the specimen's surface. This enables the use of unsanded specimens in many applications.
The standard specimen (as shown in the front view of Figure 1) is 3 inches long, 0.75 inches wide, and can be up to 0.50 inches thick. The commonly used specimen has a thickness of approximately 0.1 inches. If necessary, the fixture can also accommodate shorter and narrower specimens. Each edge of the specimen is machined with a 90° notch, and a strain gauge can be installed on the surface of the specimen in the notched area to monitor shear strain.
I. Core Mechanism of the KRL Test The KRL test (CEC L-45-A-99 standard) evaluates the shear stability of polymer additives (such as viscosity index improvers VIIs and anti-wear agents) in lubricating oils by simulating high-shear stress environments (e.g., gearboxes, hydraulic systems). Its core influencing mechanisms are as follows: 1. Mechanical Shear Degradation: - During the test, tapered roller bearings operating at 1500 rpm and under a 5000 N load generate shear rates as high as 10⁶~10⁷ s⁻¹, causing the breakdown of long-chain polymer molecules (reduction in molecular weight). For example,
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