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Cyclic load experiments are reported for two epoxies, one containing rubber particles. With and without interruptions during unloading, the experiments were performed on an Instron machine at a constant rate of head motion using an averaging extensometer capable of strain to fracture and having no dead zone. Results of interrupted unloading tests show the effect of elasticity of the portion of the specimen outside the gage length on the observed stress-strain curves.

Means are described for raising by a factor of about three the allowable cyclic pressure provided by a high pressure fatigue machine for fatigue testing of thick-walled tubes. Fatigue test results are given for 7.9- and 6.4-mm high pressure tubing of 316 (Unified Numbering System [UNS] S31600) stainless steel, crosses, tees, and seals.

An instrument is described for measuring circumferential strains in plastic specimens of circular cross section. It consists of four direct-current differential transformers (DCDTs) suitably mounted on an invar ring. The DCDTs probe the position of the surface of the specimen at opposite ends of two mutually perpendicular diameters. Examples of performance are given for creep of a thin-walled tube of polyurethane.