Single Edge Notched Bending Tests Research Articles

The effect of amine/epoxy ratio on the fracture toughness of tetrafunctional epoxy resin

The effect of amine/epoxy ratio on the fracture toughness(KIc) of tetrafunctional epoxy resin was investigated. KIc value was measured by single-edge notch-bend test. The KIc value of the tetrafunctional epoxy resin increased with increasing the amount of amine curing agent. This result was explained with the structural viewpoint of the epoxy network. The network structure of the tetrafunctional epoxy was analyzed with dynamic thertnomechanical measurement and in-situ near IR technique.

The influence of cyclic fatigue damage on the fracture toughness of carboncarbon composites

The influence of cyclic loads on the fracture toughness of a tightly woven carboncarbon composite was investigated as a function of stress levels. Results of fracture toughness tests were correlated with microstructural examination using scanning electron microscopy (SEM). Values for the stress intensity factor, K Ic, were determined using the ASTM single-edge notched bend test. Results were discussed in terms of the effects of applied cyclic stress levels and the relationship of the load-displacement curves. The fracture toughness of the composite remained unaffected when the maximum tensile load in the fatigue cycle was up to 80% of the static tensile strength. However, a decrease in the fracture toughness was determined when it was exposed to cyclic loads above this threshold stress level. Changes in texture associated with cyclic fatigue were determined in the matrix of this composite.

CeO<SUB>2</SUB>安定化ZrO<SUB>2</SUB>の混合モード下における破壊挙動および破壊靭性

The fracture toughness of CeO2 stabilized ZrO2 (CeO2-ZrO2) has been measured under mode I, mode II and their mixed-mode conditions. The conventional single-edge-notched bending (SENB) test was carried out to obtain the mode I fracture toughness. The anti-symmetric four-point bending (AS4PB) test, which is the modified SENB test, was adopted for the mixed-mode and mode II fracture toughness tests. The obtained stress intensity factors at unstable fracture were discussed with the phase transformation behavior of ZrO2 and the phase-transformation toughening mechanism.The results showed the maximum principal stress criterion and the non-coplanar strain energy release rate criterion is applicable to the KI-KII fracture curve. Under the mode II loading condition, the KIIC/KIC value of CeO2-ZrO2 was 0.6, which was lower than those of non-transforming brittle materials. The low KIC/KIIC value is attributed to the shielding effect by the transformation which is effective only on the mode I stress intensity.

The fracture toughness testing of ceramics and acoustic emission

Measurements of the fracture toughness of commercial sintered alumina were monitored using acoustic emission to detect subcritical crack growth. Double-cantilever-beam specimens gave higher values of toughness than single-edge-notched bend (SENB) or double-torsion specimens did, even after correction for slow crack growth. The SENB test with a sharp crack appears to give the most reliable results, requires the easiest specimens to prepare and suffers the least slow crack growth. In view of this, detailed studies of the damage made by sawing notches, of the effects of the a/W ratio and of the cross-head displacement rate were made for SENB specimens. Sharp cracks with small a/W ratios and high cross-head speeds minimize the effects of slow crack growth.