Impact testing, avoiding

The Izod impact test may indicate the need to avoid inside sharp corners on parts made of such materials. For example, nylon and acetal-type plastics, which in molded products are among the toughest materials, are notch-sensitive and register relatively low values on the notched Izod impact test. 

Until now we have studiously avoided defining what constitutes an explosion or go result in an impact test, except mentioning that go s are judged on the basis of sound, flash, gas volume etc. What physical events produce these observed manifestations Based primarily on the studies of Bowden (Ref 2) it is clear that in an impact test explosion frequently starts as a relatively mild deflagration which can propagate as slowly as lOm/sec, which turns into a much more violent deflagration, (lOO-lOOOm/sec), in the confined (by striker anvil) explosive. For many insensitive explo-... 

Low-temperature embrittlement occurs in carbon and low-alloy steels at temperatures below their brittle-ductile transition temperature range. The effect is reversible when the alloy is heated above the transition range, ductility is restored. This embrittlement is avoided by following the Charpy impact test requirements of the relevant engineering codes. The need to test depends primarily on the material, its thickness and the minimum design temperature. 

Since impact testing is a major exjiense to the manufacturer of a pressure vessel, the designer should do every thing to avoid it. Impact testing can always be avoided but may not be the most economical alternative. Following these steps will help eliminate the need for impact testing and, at the same time, will provide the lowest MDMT. 

INCREASE VESSEL HEAD AND/OR SHELL THICKNESS DETERMINE THE TEMPERATURE REDUCTION NEEDED TO AVOID IMPACT TESTING, USE UCS 66 (b) TO DETERMINE THE STRESS RATIO REQUIRED AND CALCULATE THE CORRESPONDING THICKNESS. 

EVALUATE IF THE MATERIAL SHOULD BE REVISED TO A TOUGHER MATERIAL TO AVOID IMPACT TESTING... 

Adhesive manufacturers have made significant efforts over the last several years to develop toughened systems that can pass these cold impact tests. The first step toward meeting this requirement is fine-tuning the curing process of the adhesive to avoid brittleness and improve fracture toughness. The use of specially formulated accelerators can help adjust the cure rate and improve toughness. 

AU automotive components that will be used in areas subject to potential vehicle impact require topcoats that involve highly flexible clearcoats. This is needed to avoid a drastic reduction of energy absorption upon impact. In instrumented impact tests, elastomeric-modified PC blends perform giving excellent results as high as 100 Nm at 23°C and show very little loss down to 40°C. If the specific requirement for the coated part is, for example, that the performance shall be more or less maintained without any brittle failure at -20°C, the flexible nature of the clearcoat can be adjusted accordingly using the instrumented impact method (2). More often however, the performance specification is defined according to the OEM requirement for a complete bumper system. 

Agricultural Products. Pesticides are frequendy appHed as emulsiftable concentrates. The active insecticide or herbicide is dissolved in a hydrocarbon solvent which also contains an emulsifier. Hydrocarbon solvent selection is critical for this appHcation. It can seriously impact the efficacy of the formulation. The solvent should have adequate solvency for the pesticide, promote good dispersion when diluted with water, and have a dash point high enough to minimise dammabiUty ha2ards. When used in herbicide formulas, low solvent phytotoxicity is important to avoid crop damage. Hydrocarbon solvents used in post-harvest appHcation require special testing to ensure that polycycHc aromatics are absent. 

If a flame arrester is provided with cowls, weather hoods, deflectors, etc., it must be tested for the configuration involved if the test is done to meet the UL, USCG, or CEN standard (see Chapter 8). Maintenance of a flame arrester should be performed carefully to avoid any adverse impact on arrester performance (see Chapter 7). All flame arresters should be inspected regularly as operating experience dictates (see Chapter 7). 

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