Experiment scratch test

Recently, Sarin (1995) developed a new version of the scratch test, who turned the experiment on its side and performed a micro-scratch test on the cross section of the sample, as shown in Fig. 22.11. After the edge of the cross section is precisely polished, the scratch test is carried out on a microscopic scale. As a result, the failure mode can be isolated and... 

The main value of salt-spray tests is in the evaluation of the effectiveness of phosphate coatings in restricting the spread of rust from scratches or other points of damage in a paint film. This feature is of particular interest to the motorcar industry, as vehicles are often exposed to marine atmospheres and to moisture and salt when the latter is used to disperse ice and frost from road surfaces. Great care is needed in the interpretation of a salt-spray test, as it has been found to favour thin iron phosphate coatings more than is justified by experience with natural weathering. In the motorcar industry the present custom is to use zinc phosphate coatings on the car bodies and all other parts exposed to the outside atmosphere. 

Ware Washing. Thoroughly wash laboratory ware before using it in an experiment. First rinse it with tap water. If the dirt is not removed, use a special test-tube brush. Never wash ware with water and sand because scratches may appear on the glass that detract from its strength. 

These tests focused on the determination of a materials resistance to localized (pitting) corrosion. To accomplish this goal, three types of electrochemical experiments were conducted (cyclic polarization, electrochemical scratch, and potenti-ostatic holds) to measure several key parameters associated with pitting corrosion. These parameters were the breakdown potential, EM, the repassivation potential, Etp, and the passive current density, tpass. 

Another possibility mentioned above is the addition of nanoscale particles to a liquid matrix system where the nanoscale particles are grown outside of the system. Experiments have been carried out with boehmite in a matrix derived from Si(OR)4/Al(OR)3 and glycidyloxypropyl triethoxy silane (GTPS) [22]. Even the addition of 5 % by volume of y-alumina or boehmite leads to systems which show a remarkably increased scratch-resistance compared to the unfilled material. The optical transparency is not influenced if the particle size of the boehmite is below 20 or 30 nm. In Fig. 21 the scratch resistance by the Vickers diamond test of the unfilled system is compared to the filled system and, as one can see, the scratch resistance is increased remarkably. 

After extensively interviewing human experts and doing experiments using an early version of the prototype system, we found two important characteristics of the test planning methods used by human experts in this domain. Firstly, experts do not always make a detailed plan. They make a plan at an appropriate level of abstraction, a rough plan for one purpose and a detailed plan for another purpose. Secondly, they do not make any plan from scratch. Experts have various kinds of "templates which they use as the starting point of their planning or as part of a plan. These two characteristics are explained in more detail below. 

Skin tests are often useful. They are commonly carried out by intradermal injection, but prick, scratch and patch tests may be used (Aldrete and Johnson 1969, 1970). Incaudo et al. (1978) obtained positive results only in 5 (8%) of the 59 patients they reported. Furthermore, the information gained from the skin test results was of little value since some of these were false positives. We had a similar experience in 18 patients with suspected acute reactions to local anaesthetics. Clearly positive results were obtained in only 2 patients, but further investigations carried out in those 18 patients cast further doubt on the validity of skin tests. These investigations are detailed in Chap. 6. 

MPa. The evidence of GBS is the displacement of the scratch lines during creep testing. This figure shows scratch lines displaced across a grain boundary transverse markings are inscribed perpendicular to the tensile axis. Clear offsets may be seen in the transverse marker line in this Mg-0.78 %A1 alloy. The tensile axis in this experiment is horizontal. An alternate method for evaluating GBS is by means of interferometry. An example of the offsets of the same alloy as revealed by interferometry is visible in Fig. 6.75. 

For brittle thermosets, parallel-sided dumb-bell or waisted dumb-bell specimens are preferred simple parallel-sided specimens often fail in the jaws of the testing instrument. Moreover, in our experience, sample preparation is absolutely critical. Even minor imperfections and scratches on the surface of the specimen can lead to failure occurring in times several orders of magnitude earlier than expected. 

All friction experiments were conducted at room temperature using a 1500-g load sled at a speed of 2.54 mm/s for a total test time of 24 s. The measured friction force was automatically recorded by the microprocessor at a maximum rate of 3906 samples/s. Each dry-film lubricant was used to prepare two to three coated specimens, each of which was tested two to three times for a total of four to nine measurements. These values were averaged, and the resulting COF and standard deviation values were used in further analysis. Nitrile gloves were used to handle the test specimens, and extra care was taken to prevent contamination of the test specimen surface. After each run, the three balls were wiped with an acetone-soaked Kimwipes and, if noticeable scratching of the ball occurred, the balls were rotated to provide undisturbed test surfaces. Between each dry-film lubricant formulation, the balls were replaced. A detailed description of the friction test procedure can be found in the literature [35]. 

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