Static deflection measuring devices

Many semi-static devices have been developed ever since the first semi-static deflection measuring device, the California Travelling deflectograph in the early 1950s, was presented in Hveem s paper (1955). A good historical review of the evolution of semi-static deflection measuring devices can be found in the Andren report (Andren 2006). 

This paragraph covers most of the semi-static deflection measuring devices currently in use. 

The non-destructive structural evaluation of a pavement may be carried out by a wide variety of deflection measuring devices. The devices may be classified into three categories (a) static devices, (b) semi-static devices and (c) moving or rolling devices. 

A general description of the various types of static and semi-static deflection testing devices and procedures for deflection measurement is provided by ASTM D 4695 (2008) or AASHTO T256 (2011). 

Classical, macroscopic devices to measure friction forces under well-defined loads are called tribometers. To determine the dynamic friction coefficient, the most direct experiment is to slide one surface over the other using a defined load and measure the required drag force. Static friction coefficients can be measured by inclined plane tribometers, where the inclination angle of a plane is increased until a block on top of it starts to slide. There are numerous types of tribometers. One of the most common configurations is the pin-on-disk tribometer (Fig. 11.6). In the pin-on-disk tribometer, friction is measured between a pin and a rotating disk. The end of the pin can be flat or spherical. The load on the pin is controlled. The pin is mounted on a stiff lever and the friction force is determined by measuring the deflection of the lever. Wear coefficients can be calculated from the volume of material lost from the pin during the experiment. 

Potter et al. (1976) have measured the bubble velocity as a function of drive field for bubbles in rf sputtered films. They have shown that magnetic annealing lowers the coercivity. They have measured the wall mobility and dynamic coercive force and presented the first conclusive data on the existence of gyrotropic deflection in an amorphous material. Minkiewicz et al. (1976) have shown that for samples prepared by rf sputtering, Cu dilutes the transition metal sublattices much differently than Mo. But overall the static coercivity in as-deposited films is larger than one would desire for device applications, and it is lowered by annealing treatments (Potter et al., 1976). 

Dynaflect and Road Rater are vibrating load devices developed in the United States in the 1970s. They measure dynamic deflection while they are stationary, using a sinusoidal force. Unlike the Benkelman beam and semi-static devices, they are also capable of measuring the deflection basin since deflection is recorded by velocity transducers (usually five). Both devices comply with ASTM D 4695 (2008) and ASTM D 4602 (2008). 

The first experiments have been carried out by the LCPC putting the projector and the camera on a static fatigue device. The first applications showed interesting results, which validate the choice of measuring deflection basin with fringe projection. However, this technique needs to be improved in order to obtain an operational device. An ongoing project aims to mount the system on a heavy truck (Muzet et al. 2009). 

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