Evaluation of tensile yield strength of high-density polyethylene in flat-ended cylindrical indentation: An analytic app
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Evaluation of tensile yield strength of high-density polyethylene in flat-ended cylindrical indentation: An analytic approach based on the expanding cavity model Jongho Wonb)1, Seunggyu Kimb)2, Oh Min Kwonb)3, Young-Cheon Kim4,a), Dongil Kwon3 1
Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Korea; and Centre for Advanced Innovation Technologies (CPIT), VSB-Technical University of Ostrava, Ostrava 70800, Czech Republic 2 Facility Team, Samsung Electronics, Hwaseong 18448, Korea 3 Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Korea 4 Research Center for Energy and Clean Technology, School of Materials Science and Engineering, Andong National University, Andong, Gyeongbuk 36729, Korea a) Address all correspondence to this author. e-mail: [email protected] b) These authors contributed equally to this work. Received: 22 September 2019; accepted: 3 December 2019
The tensile yield strength of high-density polyethylene using instrumented indentation tests with a flat-ended cylindrical indenter was evaluated. The variation in the field expressed by stress and strain beneath the flatended cylindrical indenter is investigated using a new expanding cavity model to study the relation between tension and indentation. This model starts from the separation of forces into the compressive force on the material and the frictional one, which is generated during indentation on the sides of indenter. The authors propose a method to correct the frictional force based on the saturation of indentation hardening and obtain load–depth curve with compressive component only. For conversion of indentation force and displacement, our new representation model is applied. By modifying Johnson’s model, the new assumption of conservation of indentation plastic volume is suggested. This model proves and supports conventional relations of the strain rates between indentation and tension theoretically. These are verified through the experiments: instrumented indentation and uniaxial tensile test. The authors find a good agreement between the tensile yield strengths at various strain rates.
Introduction High-density polyethylene (HDPE) has been widely used in industrial areas such as water, oil, and gas pipelines due to its good chemical resistance and low installation and maintenance costs. Thus, their failures cause enormous economic damage, so the importance of safety and reliability is greatly increasing as the amount of HDPE pipelines increases [1, 2]. Frequent monitoring of HDPE pipe for safety and reliability is thus essential. HDPE is a material with both hyperelasticity and elastic–plasticity properties. Because of these properties, various attempts [3, 4] have been made to evaluate the mechanical properties of HDPE. Unlike various attempts, ultrasonic testing and visual inspection are the main techniques of reliability evaluation of HDPE pipe in field, but these methods are qualitative only. In addition, tensile testing, another way to
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