A-A-52446 Sheet Molding Compound: Low Shrinkage (Metric)This CID covers requirements for a high strength, low shrinkage, sheet molding compound (SMC) and molded plastic parts made therefrom. The low shrinkage property imparts dimensional stability to the molded parts. Items made from this material are primarily used for nonappearance, high strength body panels that are not painted.

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A-A-52446

(b) Environmental conditions. The SMC molded parts shall be capable of withstand exposure to the following high and low temperature and humidity conditions without showing evidence of any functional/visual degradation or embrittlement:

(1) High temperature of 70 ± 3° for 168 hours.

(2) Low temperature of -40 ± 3° for 4 hours.

(3) Relative humidity, as follows:

Step 1.

Gradually raise the internal chamber temperature and RH from room ambient to 60°C and RH to 95 ± 5% for a period of two hours minimum.

Step 2.

Maintain the conditions of step 1 for a period of six hours minimum.

Step 3.

Reduce and maintain RH at 85% minimum and gradually reduce the internal chamber temperature to 30°C in eight hours.

Step 4.

Increase RH to 95 ± 5% and maintain temperature at 30°C for an additional eight hours.

Step 5.

Repeat steps 1 through 4 for a total of 10 cycles and not less than 240 hours.

Step 6.

Near the end of the fifth and tenth cycle, while still at 30°C and 95% RH, visually and functionally check the item.

TABLE I. Physical and mechanical properties.