Loaded wheel test

The mix design procedure for micro-surfacing according to ASTM D 6372 (2010) requires the execution of the following tests (a) cohesion test, (b) wet track abrasion test, (c) loaded wheel test and (d) classification test, all described in ASTM D 6372 (2010). 

The loaded wheel test measures the amount of compaction and displacement characteristics of a micro-surfacing mixture under simulated rolling traffic compaction. 

The loaded wheel test is also included in the mix design method proposed by ISSA A143 (2010) and is carried out using a similar procedure described in ISSA TB-147 (1990). 

Fig. 12-18 The wet track abrasion test and loaded wheel test of cured microsurfacing specimen prepared with five different polymers reported by Jones [23, 24].

Wheel tracking test specimens were prepared by compacting asphalt mixtures into a mold of 300 by 300 mm, and 50 mm in depth, with a roller compactor. The test apparatus is a machine in which a loaded wheel with a solid rubber tire of 200 mm diameter and 50 mm wide is rolled to and fro on a specimen of an asphalt mixture. A photograph of the apparatus is given as Fig. 2. 

Before the test, the specimens are subjected to a conditioning run for 1000 loading cycles at a temperature between 15°C and 25°C. It is highlighted that one loading cycle is two passes (outward and return) of the loaded wheel. 

Cyclic loading tensile tests (Fig. 7.10) to determine fatigue failure are common for metals used for wheel rims in trains or for wings in airplanes but they are not routinely performed on polymeric materials. It is known that steel has an endurance limit but it is... 

TWI = Taber Wear Index. CS-10 abraser wheels, 100 gram load, determined as average weight loss per 1000 cycles for total test of 6000 cycles. 

The hardness and abrasion resistance of anodic coatings have never been easy properties to measure, but the development of a British Standard on hard anodising has made this essential. Film hardness is best measured by making microhardness indents on a cross-section of a film , but a minimum film thickness of 25 tm is required. For abrasion resistance measurements, a test based on a loaded abrasive wheel , which moves backwards and forwards over the film surface, has improved the sensitivity of such measurements. 

There is usually more than one test method to determine a performance because each test has its own behavior and meaning. As an example there are different tests used to determine the abrasion resistance of materials. There is the popular Taber abrasion test. It determines the weight loss of a plastic or other material after it is subjected to abrasion for a prescribed number of the abrader disk rotations (usually 1000). The abrader consists of an idling abrasive speed controlled rotating wheel with the load applied to the wheel. The abrasive action on the circular specimen is subjected to a rotary motion. 

Abrasive wear is a complex combination of a number of factors, including resilience, stiffness, thermal resistance, thermal stability, resistance to cutting, and tearing (Smith, 1993). There are a number of laboratory tests, both international standards and commercial tests, for the evaluation of abrasive wear. The results from these tests normally represent only an indication of the actual wear that can be found in practice. The test equipment generally has a loaded sample against course abradant or, in the case of a Taber abrader, a loaded abrasive wheel against a flat sample (see Chapter 8). 

Dynamic heat buildup in applications such as wheels is important. Polyurethanes with a high resilience or a low tan 8 in the operating range are important. Polyurethane elastomers used in wheel applications can be evaluated using a test rig where the urethane can be run under load for a fixed period or until failure. 

A typical test speed is 32 kph at a load of 55 kg. The surface temperature of the wheel can be measured using an infrared thermometer. Failure will be due to hysteresis work, and the part will decompose from the inside out. 

A roller may be subjected to pressure in a hydraulic press to simulate actual service conditions. The deflection at various loads can be noted. Wheels can be run on a test rig at service speeds under a load and the life and heat buildup recorded. 

In order to evaluate the resistance to deformation, the testing wheel loaded with 686 N was shuttled across the center of the specimen 42 rounds per minute at 60 C, and the dynamic stability (DS) (passes/mm) was measured by using the following equation. 

Another test method (ASTM D-3527) is used for the evaluation of grease life in tapered roller wheel bearings in a model front wheel assembly run at 1000 rpm under a specified thrust load at 160°C (320°F) with a cycle of 20 h on and 4 h off (ASTM D-4290). 

Armstrong Abrasion Test This test measures abrasion resistance of a flat surface by rotating a 10 cm diameter specimen disk beneath an abrasive under load. A 1,000 g load was used on a Calibrase wheel No. CS-17F. 

In this test a notch of initial depth c is introduced, usually by using a diamond wheel, on the tensile side of a flexure specimen (Fig. 11,6a). The sample is loaded until failure, and c is taken as the initial crack length. Fracture toughness K c is calculated from... 

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