Study of Damage and Fracture Toughness Due to Influence of Creep and Fatigue of Commercially Pure Copper by Monotonic an
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INTRODUCTION
THE life prediction for highly and complex loaded engineering components is always an important issue. Determination of mechanical properties of materials either from small amount of test material or on component is one of the major challenges. Various nondestructive test techniques are used to investigate the material integrity, but none of these techniques are used to evaluate tensile properties of material using an analytical relation. Among the small specimen techniques, the shear punch, miniaturized disk bend tests (MDBT), and ball indentation test (BIT) are quite attractive for evaluating the mechanical properties of materials. Although MDBT and shear punch test can generate load–deflection (P-d) data, it is not straightforward to analyze and to transform those data to uniaxial tensile stress–strain data, which are of more engineering significance because of their wide use and acceptance. A great number of papers concern the determination of the plastic properties describing the stress–strain curve from indentation test.[1–20] Most of the researches are focused on the indentation behavior at monotonic loading conditions. On the other hand, very few researchers worked on cyclic indentation. Some researchers used cyclic indentation to assess accurately plastic characterization beneath the indenter,[21] the phase transformation under indentation stress,[22,23] the failure of coatings,[24,25] and others.[26,27] All these cyclic SABITA GHOSH, Principal Investigator, is with the Council of Scientific & Industrial Research, National Metallurgical Laboratory, Jamshedpur 831007, India. Contact e-mail: sabita_ghosh@rediffmail. com; [email protected] RAGHU V. PRAKASH, Associate Professor, is with the Indian Institute of Technology Madras, Chennai 600036, India. Manuscript submitted November 2, 2011. Article published online September 1, 2012 224—VOLUME 44A, JANUARY 2013
indentation tests were carried out by repeating several indentations. A limited amount of indentation fatigue studies has been carried out, and these tests have shown the possibility of establishing the relationship between conventional fatigue tests and the indentation fatigue tests.[28–38] It has been observed that the indentation depth could grow and the indenter could sink further into the samples under cyclic loading conditions. Most of the work has been done either by Vicker’s indenter or by flat cylindrical indenters. The main difficulty with Vicker’s indenter is to characterize the change in the contact area between the indenter and the sample. The flat cylindrical indenter in certain cases has some advantages over indenters with other shapes. The early indentation fatigue test was carried out on b-tin single crystals by Chu and Li.[30] They found that the indentation depth could increase with the number of cycles. Xu et al.[32] studied the effect of indentation fatigue on a poly(vinyl chloride) bulk material and on two different films/coatings, TiN and NiP, deposited on 304 stainless-steel substrates and established indentation fatigue as
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