Abstract
This article presents an experimental study that clarifies the relationship between the initial fracture stress and fatigue limit of glass fiber reinforced unsaturated polyester resin specimens with a laminated structure taken from a pultruded square pipe. Quasi-static bending and tension tests are performed with acoustic emission (AE) measurements to identifying the occurrence of initial fracture during testing. AE and observation results have clarified the occurrence of initial fracture was detected by maximum acoustic energy values and corresponding fiber breakage in the unidirectional (UD) bundles. Moreover, the ratio of initial fracture stress to ultimate strength is 32% in bending and 26% in tension, when comparing stress and strains on the tension side of the UD layer. These values are in good agreement with each other and with the measured tensile fatigue limit when the cyclic stress is at 25% of the tensile strength. Initial fracture stress obtained by static tests is close values to the fatigue limit which will greatly contribute to the prediction of the fatigue limit.
Highlights
Global warming is a serious problem which causes increase average temperature and sea temperature and sea-level rise
We investigated the relationship between the initial fracture and fatigue limit of glass fiber reinforced unsaturated composite
This study showed the relationship between the initial fracture stress and fatigue limit of glass fiber reinforced unsaturated polyester resin specimens
Summary
Global warming is a serious problem which causes increase average temperature and sea temperature and sea-level rise. Wisnom et al [6] investigated the fatigue behavior of pseudo-ductile unidirectional thin-ply carbon/epoxy-glass/epoxy hybrid composites They tested specimens in static tension to determine the fragmentation initiation stress level. When the same pristine samples were tested in fatigue at stress amplitudes significantly lower than the stress initiation level, no stiffness reduction up until 105 cycles was observed as a result of being loaded well below the first carbon layer fracture strain [6]. Damage growth in the material was characterized by evaluating degradation in stiffness They observed that with increasing stress amplitude levels, the number of cycles to failure was significantly reduced. Echtermeyer et al [9] evaluated the lifetime and Young’s modulus changes of glass/phenolic and glass/polyester composites under fatigue They performed static tension and compression on the samples, and later tested their tensile and compressive fatigue properties at varying stress amplitudes. The tensile fatigue test was conducted to clarify the relationship between fatigue properties and initial fracture stress
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