The way in which the time of exposure to the atmosphere modifies both
the elastic properties and the ultimate strengths of sheet moulding co
mpounds has been evaluated. Various plates of this material were expos
ed to the elements over a total period of 2 years, periodic tests bein
g carried out every 6 months. As well as the static mechanical propert
ies, the dynamic flexure properties have also been obtained for differ
ent frequencies and over a range of temperatures from 20 to 250-degree
s-C.