The paper presents results of experiments in which the thermal expansion and swelling behavior of an epoxy resin system and two graphite/epoxy composite systems exposed to water were measured. It was found that the cured epoxy resin swells by an amount slightly less than the volume of the absorbed water and that the swelling efficiency of the water varies with the moisture content of the polymer. Additionally, the thermal expansion of cured epoxy resin that is saturated with water is observed to be more than twice that of dry resin. Results also indicate that cured resin that is saturated with 7.1% water at 95 C will rapidly increase in moisture content to 8.5% when placed in 1 C water. The mechanism for this phenomenon, termed reverse thermal effect, is described in terms of a slightly modified free-volume theory in conjunction with the theory of polar molecule interaction. Nearly identical behavior was observed in two graphite/epoxy composite systems, thus establishing that this behavior may be common to all cured epoxy resins.

Thermal expansion and swelling of cured epoxy resin used in graphite/epoxy composite materials

Contents include: Complete coverage of SCC for a variety of materials and SCC in different environments: carbon and low-alloy steels high-strength steels stainless steels nickel-base alloys copper alloys aluminum alloys magnesium alloys titanium alloys zirconium alloys uranium alloys amorphous alloys glasses and ceramics weldments in boiling water reactor service.

Stress-corrosion cracking

Environmental fatigue behavior and life prediction of unidirectional glass–carbon/epoxy hybrid composites

Unidirectional glass fiber reinforced and glass–carbon fiber reinforced (glass to carbon fiber volume ratio 3:1) epoxy matrix composite samples were subjected to tension–tension fatigue in air and in distilled water at 25°C. While no significant change in fatigue life was observed for both types of samples tested in air and in water when cyclically tested at 85% of average ultimate tensile strength (UTS), the detrimental effect of water becomes apparent at lower stress levels of 65 and 45% UTS. Compared to samples tested in air, cyclic loading in water results in shorter fatigue lives for both glass and hybrid samples. While all of the glass fiber composite samples did not survive to 106 cycles when loaded in water, hybrid samples showed better retention in structural integrity under environmental fatigue for lives up to 107 cycles, a consequence of the corrosion resistant of carbon fiber. Thus, by incorporating appropriate amount of carbon fibers in glass fiber composite, a much better performance in fatigue can be achieved for glass–carbon hybrid composite.

Environmental fatigue of unidirectional glass-carbon fiber reinforced hybrid composite

The study of static and dynamic behavior of environmentally conditioned fibre reinforced polymeric (FRP) composites is necessary and crucial to examine the durability, reliability and sustainability of these noble materials. FRP composites are being used all around the globe and substituting the conventional materials, starting from mini toys to large aerospace components. Present review has introduced to accumulate and understand the disseminate literature in concentrating the significance of understanding the static and dynamic behavior of FRPs with changing environmental conditionings (hygrothermal, low and high temperature, salt solution, freeze thaw, UV light) and with the interaction of different nano-fillers. Their stability and integrity in diverse service environments may be reformed by their reactions against different nature of loadings i.e. static or dynamic and the components such as fibre, matrix and fibre/matrix interfaces in those environments. The static and dynamic states of loading may come with a possible weaker region to encounter the durability and integrity of the composites. To understand the exact failure modes that correlates the position of environmentally conditioned interfaces and dynamic state of loadings, thus confusing the estimation of its overall performance and mechanical behavior. Interface reliability and durability is vital since in-service environments the degradation in the interfacial region leads to complete composite failure. Therefore, the study of combined effects of various in-service environmental conditions and the role of static and dynamic behavior on the interface will be a crucial part related to the multiaxial dynamic states of failures occurring in FRP’s.

Static and Dynamic Behavior of Fibrous Polymeric Composite Materials at Different Environmental Conditions

Torsional and flexural fatigue tests were performed on both uniaxial (0 deg) and crossplied (plus or minus 45 deg) graphite-epoxy materials at temperatures of 24 and 74 C in environments of air and water. The results of the torsion testing showed that the number of cycles required to cause an initial decrease in stiffness as well as the rate of stiffness loss was a function of temperature and environment; the most significant losses were noted for tests at the higher temperature in water. The torsional fatigue specimens were subsequently tested in four-point bending to determine the effect of torsional damage on longitudinal properties. This damage caused changes in the flexural stiffness, failure stress, and failure energy, depending on the stress and environmental histories. The flexural fatigue tests also showed a significant effect of water (at 24 C) on the material behavior. These results are compared with the results of previous investigations and are discussed in terms of proposed damage mechanisms.

HT Sumsion

Papers

Effects of environment on the fatigue of graphite-epoxy composites