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In agricultural equipment used for tillage, abrasion by hard particles is a major mode of wear. Field tests and customer surveys of equipment usage can provide valuable data on the rate of wear of different soil working tools. However, it is usually very time consuming and costly to gather this type of information. While field testing will continue to play an important role in the evaluation of agricultural equipment durability, the use of laboratory tests that adequately simulate the wear modes occurring in the field can significantly reduce the amount of field testing required to evaluate wear of tillage tools. In this review, important criteria for determining the degree to which laboratory tests simulate the wear occurring in field tests or service will be presented. These include not only a comparison of the wear rate and relative wear resistance determined from laboratory and field tests, but also a comparison of the worn surfaces to identify the wear mechanisms that are active. Widely used abrasion tests, including the ASTM G65 Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus and the G105 Standard Test Method for Conducting Wet Sand/Rubber Wheel Abrasion Tests will be reviewed, and their ability to simulate the wear that occurs in tillage operations will be examined. Examples will be provided that highlight the strengths and weaknesses of these laboratory tests in ranking the abrasion resistance of materials used in soil working tools. A major limitation of all of these tests is their inability to simulate wear that occurs under the combined action of soil abrasion and repeated impacts by rocks. Difficulties associated with the gathering of quantitative field data needed to carry out the comparison of laboratory and field test results will also be discussed.

This paper reports the first quantitative relationship between shape and abrasive wcar rate of steel.

In this paper the authors infer that the laboratory test they have developed simulates the wear that occurs in main bearings of XHP 3 rock bits. While they do present some results of their laboratory tests, they do not compare these results with those from field tests so that the degree of correlation is established. Recently, important aspects of simulating wear that occurs by abrasion in various service enviroments have been thoroughly reviewed by Moore.2 Much of his review may be applied to other types of wear, as well. One important way of assessing extent to which a laboratory test duplicates the wear occurring in a particular service environment is to determine if the same wear mechanisms are present. This can be done by comparing the worn surfaces and the wear debris that are produced. Although the authors do include some photographs of the wear debris and worn surfaces produced by their laboratory test, they do not present photographs of the surfaces of worn main bearings or of the spindles that were in contact with these bearings. Furthermore, there is no discussion of the type of wear debris that are generated during the operation of the rock bits. Were the worn surfaces of used main bearings and spindles examined and the wear debris also? If such an examination has not been carried out, then I would recommend that it should be done so that the degree to which the laboratory test simulates main bearing wear is determined.In Figs. 9-11, in which photographs of wear debris and worn surfaces are displayed, the figure captions indicate that these were obtained from tests in which the load was 43.08 MPa which is greater than the critical load shown in Table 1. Have the authors also collected photographs of wear debris and worn surfaces of test specimens run at loads below the critical load? If so, what differences did they observe? If they have not collected such photographs, I believe that this should