ABSTRACT
A modified single edge cracked bend beam specimen called "inclined edge crack asymmetric bend" (IE-CAB) specimen was designed and proposed for investigating mixed mode I/II fracture toughness behavior of brittle materials. Using a large number of finite element analyses performed for different geometry and loading conditions, it was demonstrated that unlike the conventional single edge notch beam specimen, the IE-CAB configuration can provide full combinations of mode mixities from pure mode I to pure mode II. Then the IE-CAB specimen was employed for mixed mode I/II fracture toughness testing of two PMMA based denture materials (i.e. neat PMMA and toughened PMMA with Nano-hydroxyapatite (HAP)and Nano-alumina (Al2O3) particles). The obtained experimental results showed that adding bio-compatible (HAP and Al2O3) Nano-particles can increase both modes I and II fracture resistance (KIc and KIIc) values of base PMMA denture. However, the influence of such particles was more pronounced on enhancing mode I fracture toughness (KIc) value. Pure mode II fracture toughness value was obtained less than the pure mode I fracture toughness in the tested specimen showing the higher crack growth risk of such PMMA base dentures against dominantly shear loads. The well-known maximum tangential stress theory was also used for estimating the obtained experimental data both for mixed mode fracture toughness and fracture initiation direction in the tested PMMA base denture materials.
