Thermosetting Resin System Research Articles

Static and Dynamic Mode II Strain Energy Release Rates in Toughened Thermosetting Composite Laminates

In this work, the static and dynamic Mode II fracture properties of several thermosetting resin-based composite laminates are presented. Two classes of materials are explored. These are homogeneous thermosetting resins and toughened, multiphase, thermosetting resin systems. A new dynamic Mode II test is presented for composite laminates based on an end-notched flexure (ENF) specimen geometry. The specimen is impacted in three-point bending with an instrumented impact tower. Fracture initiation and propagation energies under static and dynamic conditions are determined analytically and experimentally. The test results show that the toughened systems provide superior fracture initiation and higher resistance to propagation under dynamic conditions. The results indicate that static fracture testing is inadequate for determining the fracture performance of composite laminates subjected to conditions such as low velocity impact. A good correlation between the basic Mode II dynamic fracture properties and the performance in a combined material/structural compression after impact (CAI) test is found. The results underscore the importance of examining rate-dependent behavior for determining the longevity of structures manufactured from composite materials.

Activation energy determinations from dielectric thermal analysis of reacting polymeric systems

Methods were developed for calculating reaction activation energies from dielectric property measurements during isothermal and nonisothermal cure of thermosetting polymers. These methods were derived by assuming that features of the dielectric response occurred at unique extent of reaction values. Activation energy results were obtained through dielectric analysis for two thermosetting resin systems: a model epoxy system — tetraglycidyl-4, 4′-diaminodiphenylmethane cured with 25 parts per hundred of 4,4′-diaminiphenylsulfone hardener; and a model dicyanate blend resin, 55% (by weight) of bisphenol A dicyanate and 45% of tetrao-methyl bisphenol F dicyanate. Results were in excellent agreement with activation energies determined from differential scanning calorimetry measurements.

Behavior of Epoxy Repaired Beams under Fire

Epoxy injection techniques are widely used to repair concrete or masonry structural components damaged by earthquakes, wind, or other types of overloads. When properly performed, the effectiveness of such epoxy injection techniques has been demonstrated by numerous laboratory experiments and a multitude of successful field applications. Except for elevated temperature, fire, and creep effects, most strength properties of epoxy repaired concrete components exceed those prior to damage. Since epoxy adhesives are organic thermosetting resin systems, they are highly susceptible to softening and pyrolysis at elevated temperatures. The effects of temperature and fire on epoxy repaired concrete beams is discussed herein with a presentation of test results of both small‐ and large‐scale specimens. These test results show that both shortterm strength and stiffness of epoxy repaired beams reduce rapidly at uniform temperatures exceeding about 250 °F (121 °C). Under fire conditions, the strength reduction is primari...