Mechanical characterization of the static and fatigue compressive properties of a new glass/flax/epoxy composite material using digital image correlation, thermographic stress analysis, and conventional mechanical testing

Tensile fatigue response of a novel carbon/flax/epoxy hybrid composite under strain-controlled and stress-controlled amplitude

“…The higher fiber volume fraction and cross-ply fiber layers in Type B compared with Type A increased fiber interlocking and, thus, decreased the amount of matrix embedded in the fibers. 35 These findings agree with Manteghi et al 38 who found that glass/ flax/epoxy [0 glass =0 flax exhibited a much greater overall temperature increase than glass/flax/epoxy [0 glass =AE45 flax , suggesting that the major cause of energy dissipation is the viscoelastic properties of flax fibers, matrix deformation, crack initiation, and local viscous matrix heating. 37 TSA was a reliable tool to determine the HCFS of current composites (Figure 13, Table 2).…”

“…carbon/flax/epoxy and glass/flax/epoxy) under constant stress-controlled fatigue, which showed nearly constant moduli until failure. 18,38 Similarly, some neat flax/epoxy composites previously exhibited stiffness trends similar to the current study under strain-controlled fatigue, 28,29 whereas others showed increasing stiffness under stress-controlled fatigue. 4,[23][24][25]29 As Mahboob et al 29 argue, neat flax/epoxy composites can experience increased stiffness during stress-controlled fatigue because of structural reorientation of microfibrils within the cell wall of flax fibers to be more inline with applied stress, although increasing strainamplitude (and consequently strain-rate) may also be a contributing factor.…”

“…Tensile cyclic loading was done under strain control using conventional fatigue tests and stress control using TSA. Present data can be compared to previous studies on hybrid synthetic/flax composites and nonhybrid neat flax/epoxy composites 4,18,24,38,50,55,56 (Table 2). The current hybrid composite exhibits excellent improvement in fatigue resistance compared with previous work on nonhybrid neat flax composites.…”

“…Then, the composite plates were subjected to thermographic stress analysis (TSA) for tensile cycling under constant stress amplitude to determine high-cycle fatigue strength (HCFS) as a percentage of ultimate tensile stress (r ut ). Note that several studies 18,37,38 have proved that TSA is an appealing, reliable, and alternative method, since it requires far fewer loading cycles without catastrophic specimen failure in order to estimate the endurance limit; thus, TSA uses the HCFS as an estimate of the endurance limit of composites. Note that all strains and stresses were applied along the long axis of the composite plates, i.e.…”

“…The r ut values were previously measured to be 413.8 MPa (Type A) and 338.7 MPa (Type B) for the current composite. More details about the mechanical performance of the current two types of composites, including their stress-strain behavior is reported in Al-Hajaj et al 34 TSA surface temperature variation was recorded at each stage of cycling (see section "Surface temperature"), while the HCFS of the composite was defined as the intersection of the bilinear temperature versus stress graph 18,37,38 as indicated in Figure 13.…”