Pendulum Devices

It is simple to visualize this motion. Suppose that the initial position of mass is characterized by the angle 6q. At the instant t = 0 it begins to move. Since the force is directed along the motion, the velocity increases and at the lowest point, (x = 0 and z = /), it reaches the maximum value. As soon as a mass passes this point, the velocity begins to decrease because the force component and velocity have opposite directions. Finally, the particle stops and then the motion begins again but in opposite direction. Assuming that friction is absent, we may expect a periodic movement of the mass around the middle point. In fact, equations of a motion of this particle in the Cartesian system of coordinates are 

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The friction of road surfaces is often measured with a skid tester developed by the Road Research Laboratory17 and this has also been widely used on other surfaces and floors, including artificial sports surfaces. It is a pendulum device, the movement of which is arrested by the foot of the pendulum skidding on the surface to be measured. The skid resistance indicated can be approximately related to coefficient of friction by ... 

The most popular method used for quality control uses a pendulum device (Fig. 6.3) to measure the resistance to tear propagation (ASTM D1922). For this test, specified test samples are die cut and include a slit at one end. The tabs formed on either side of the slit are clamped into the device so that when the pendulum is released a so-called trouser leg tear force is applied along the specimen in the direction of the slit. The test device reports the maximum resistive force carried in the film. Commonly, ten specimens in both the machine and transverse direction of the film are tested. 

A torsion pendulum device was developed by the scientists at the Department of Colloid Chemistry of Moscow State University, that is, by Izmaylova et al. [35-37]. This device, shown schematically in Figure 4.11, allows one to evaluate the mechanical characteristic of thin-film behavior at both the liquid-air interface and the liquid-liquid interfaces. Nowadays, similar studies can be conducted with commercial high-sensitivity shear rheometers using a special bicone tool. 

FIGURE 4.11 Schematic illustration of a torsion pendulum device for studying the rheological properties of the interfacial adsorption layer formed at an interface between polar and nonpolar liquids. (From Izmaylova, V.N. et al., Doklady AN SSSR, 206, 1150, 1972 Izmaylova, V.N. et al., Kolloidnyi Zh., 35, 860, 1973 Izmaylova, V.N. et al.. Surface Phenomena in Protein Systems, Khimiya, Moscow, Russia, 1988.)... 

The properties of these systems were studied with the experimental methods that we have already mentioned earlier in this chapter (1) the rheological properties of the interfacial layers using the torsion pendulum device (Figure 4.11) (2) the investigation of the compression of two nonpolar droplets immersed in an aqueous surfactant solution and the measurement of the force, Xoai. necessary for their coalescence and (3) the estimation of the free energy of interaction between... 

To determine tear resistance (Elmendorf), a sample is torn with the help of a pendulum device starting from a predetermined cut. The work required for a tear of a given length is measured. The test is described in ISO 1974 (1990). 

Joints often experience impact or shock loads, and their reactions will differ depending on the rheology of the adherend and the adhesive. Another early standard is D-0950, Test Method for Impact Strength of Adhesive Bonds. It involves a relatively simple specimen (Fig. 17), but a special pendulum device is required for application of the impact shear load. 

Shear experiments ean be eonducted using a torsion pendulum device. In such experiments a horizontal beam is suspended from a rectangular strip of polymer, a rod, or a fiber as shown in Figure 39. A transient force is applied to... 

FIGURE 5.1 Charpy and Izod impact specimens, (a) Impact pendulum device, (b) loading of Charpy specimen, (c) loading of Izod specimen, and (d) dimensions of Izod specimen. (Adapted from Tensile Impact Energy to Break Plastics and Electrical Insulating Materials, ASTM Standard DI822, West Conshohocken, PA, 1999.)... 

In recent years there has been much interest in the application of polymer materials at the micro- and nanoscale as microelectronic devices are made smaller and smaller. Constantinides describes an analysis and experiments of materials at the nanoscale. An instrumented pendulum device with a diamond Berkovich indenter was used to indent polymer specimens at a rate of 0.7-1.5 mm/s. The highest impact velocity (1.5 mm/s) corresponded to an impulse energy of 250 nJ. (The Berkovich nanoindenter similar to the Vickers type is normally used for testing the hardness of a material. It has a three-sided pyramid shape. It has also... 

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