A New Approach for Investigation of Mode II Fracture Toughness in Orthotropic Materials

Abstract

Estimation of mode II fracture toughness KIIC in composite materials is known as a troublous and crucial problem. Dissipated values of KIIC that are reported in different fracture mechanics references is the evidence of the mentioned claim. This problem can signify the necessity of modification on common test methods and fixtures. The present study focuses on the causes of shear test results scattering in composite materials and presents some solutions in the form of necessary corrections that should be performed on the common test fixtures. Mixed mode I/II fracture limit curves are employed to show that the scattering in test results have strong relation with the creation of a considerable Fracture Process Zone FPZ. It is shown that common test fixtures are blind in confrontation with FPZ and are not able to active toughening mechanisms in pure mode II, correctly. Therefore, estimation of KIIC with available test fixtures has considerable standard deviation. After that, by employing some structural modifications on common fixtures, a new scheme of a shear fixture is proposed that in addition to include the FPZ effects, prepare suitable condition in order to activate the mode II toughening mechanisms. In this regard, it could be found that by applying these reforms, shear load concentration as well as the accuracy of empirical test and repeatability and reproducibility are enhanced. Furthermore, a 3D finite element method FEM was considered as the numerical method in which the Iosipesque and new fixture's specimens were analyzed by ANSYS software. It was found that by applying major amendments in the new shear test fixture, a remarkable precision in results can be obtained in comparison with the previous Iosipesque one

Mixed-modes (I/III) fracture of aluminum foam based on micromechanics of damage

“…These energy release rates are defined based on density and shape of the porous materials. For overall circular porous (Figure 4), critical energy release rate is mentioned as follows in the Equation 2 (Fakoor and Khansari, 2018; Khansari et al., 2019a, 2019b): Where, G c represents circular energy. Also, the E and υ are the elastic modulus and Poisson ratio of intact body, respectively.…”

“…These energy release rates are defined based on density and shape of the porous materials. For overall circular porous (Figure 4), critical energy release rate is mentioned as follows in the Equation 2 (Fakoor and Khansari, 2018;Khansari et al, 2019aKhansari et al, , 2019b:…”

Exploring the Capability of Acoustic Emission Technique in Early Detecting Mode I and Mixed Mode Fractures

“…Fakoor and Mehri investigated the fracture of composite materials and proposed a new method to estimate the Mode II fracture toughness. They discussed the effect of the fracture process zone (FPZ) on the Mode II fracture toughness [11]. Fracture mechanics approaches are gaining more prominence, namely the methods based on appropriate fracture criteria and simulation of the failure behaviour by associated models, however, an overview of the mixed Mode I/II criteria for fracture investigation of composite materials was already provided by [12].…”

Green Concrete Based on Quaternary Binders with Significant Reduced of CO2 Emissions

“…Therefore, in modern technology of green concrete, a great interest of scientists and practical engineers concerns the possibility of modifying the microstructure of cementbased materials by using chemically active mineral additives. These include natural pozzolans, siliceous and calcareous fly ash, silica fume, granulated blast furnace slag, lime powder, and other materials that replace the cement binder in the composition of the concrete mix, e.g., [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69]. There is also the increasingly used potential of nanotechnology, in which green concrete nanoadditives are used included in its composition, such as e.g., nanosilica, carbon nanotubes, and active chemical nanoadditives, e.g., [70][71][72][73].…”