The paper describes test specimen thickness effect on stress intensity factor (KI), and T-stresses stresses (T11 and T33) for a Compact Tension specimen. Formulations to estimate 3D KI, T11 and T33 stresses are proposed based on extensive 3D Finite element analyses. These formulations help to estimate magnitudes of 3D KI and T11 and T33 which are helpful to quantify in-plane and out-of- plane constraint effect of the crack tip. The proposed formulations are validated with the similar results available in literature and found to be within acceptable error.
This paper presents an effect of specimen thickness on crack-tip plastic zone shape and size. The shape of the plastic zone is estimated in 3D with the help of elastic and elastic-plastic finite element analyses. The results indicate that the shape of plastic zone does not correspond to classical "dog-bone shape" and the maximum plastic zone size occurs beneath the free surface, contrary to conventional shape. It is observed that for specimens with B/W=0.5, the ASTM requirement of specimen thickness to estimate K IC , the plastic zone shape and size is much larger than the one obtained in 2D plane strain analysis. The results also show a significant change in the shape and size of plastic zone in elastic and elastic plastic conditions.
Test specimen selection plays a vital role in successful transformation of laboratory fracture parameter findings to the real fracture behavior of any component. The ASTM and BSI Standard test methods for measurement of fracture toughness are dominated by high constraint specimens like Compact Tension (C(T)) and Single Edge Notch Bend (SEN(B)). However, most cracks in real time structure are shallow and surrounded by low constraint. Hence, the standard specimen like Middle Crack Tension (M(T)) in ASTM and Clamped Single Edge Notch Tension (Clamped SEN(T)) specimen in BSI, yield fracture toughness value to be test specimen dependent. The Clamped SEN(T) specimen suitable for various real pipeline (low constraint conditions) application has been widely reported in literature, that however in not the case for M(T) specimen which has scarcely reported. The 3D numerical analysis of SEN(T) and M(T) specimens with an identical flaw size for fracture toughness and constraint parameters (T-stress) under linear-elastic conditions are dealt in this article. The standard specimen that emulates low constraint fracture behaviour forms the basis for recommending suitable specimen for defined real time conditions. The conservatism associated with usage of standard specimen to find fracture parameters for an application has been quantified in this work for field implementation by practitioners in fracture mechanics.
In this work, the effect of alcoholic treatment of the multi-wall carbon nano-tube (MWCNT) on the mechanical properties of epoxy composites are investigated and compared. Nano-composites were developed by mixing 0.25%, 0.5% and 0.75wt% of MWCNT. Tensile strength, Young's modulus, and Elongation are found to be effectively improved with the addition of alcoholic functionalized MWCNT in epoxy matrix. Increased tensile strength and elastic modulus of epoxy composites loaded with the alcoholic functionalized MWCNT are observed through experimental studies. The results were compared with neat epoxy composite. These findings confirm that the improved dispersion and interfacial interaction in the composites arising from covalent bonds between the MWCNT and the epoxy matrix.
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