Distinct Advantages of Circumferential Notch Tensile (CNT) Testing in the Determination of a Threshold for Stress Corrosion Cracking (KISCC)

Stress corrosion cracking (SCC) is a vexing problem for load-bearing equipment operating in a corrosive environment in various industries, such as aerospace, chemical and mineral processing, civil structures, bioimplants, energy generation etc. For safe operation, effective maintenance and life prediction of such equipment, reliable design data on SCC (such as threshold stress intensity for SCC, i.e., KISCC) are invaluable. Generating reliable KISCC data invariably requires a large number of tests. Traditional techniques can be prohibitively expensive. This article reviews the determination of KISCC using the circumferential notch tensile (CNT) technique, the validation of the technique and its application to a few industrially relevant scenarios. The CNT technique is a relatively recent and considerably inexpensive approach for the determination of KISCC when compared to traditional techniques, viz., double-cantilever beam (DCB) and compact tension (CT) that may be fraught with prohibitive complexities. As established through this article, the CNT technique circumvents some critical limitations of the traditional techniques.

Numerical and experimental investigation of notch-induced high-speed precise shearing of 42CrMo bar

A notch-induced high-speed precise shearing method was developed for high-strength metal bars, which prefabricated V-shape circumferential notches in batch on the bar surface to make stress concentration, and applied a high-speed load to complete separation on a new type of electric-pneumatic counter hammer. The FE simulation and experimental tests were conducted; the influences of loading speed, notch depth, and axial clearance were analyzed on the fracture behavior and blank quality; the microfracture mechanism was further investigated. The results showed that the circumferential notch inhibited the plastic distortion and obtained high precision chamfered billets, with a roundness error of 1.34%, flatness error of 0.34 mm, and incline angle of 0.87°. Besides, the surface notch effectively reduced Max. impact force and fracture energy. The fractography revealed that: for the notched bar, the cracks initiated from the thin extrusion layers at the bilateral-notch tips, and from micro extrusion and intrusion at the top-notch tip. The predominant microfracture mechanism involves microvoid coalescence and forming of quasi-parabolic dimples along with the shear stress.

An analysis of fracture toughness, at third mode fracture in concretes containing fly-ash additives

This paper presents the results of fracture toughness tests of concrete with fly ash (FA), specified at the third model fracture. Concrete composites with the additives of 0%, 20% and 30% siliceous FA were analysed. Fracture toughness tests were performed on axial torsion machine MTS 809 Axial/Torsional Test System, using the cylindrical specimens with dimensions of 150/300 mm, with a circumferential notch made in the half-height of cylinders. The studies examined effect of FA additive on the parameter KIIIc. The Analysis of the results revealed that a 20% FA additive causes increase in KIIIc, while a 30% FA additive causes decrease in fracture toughness.

Notch Effects in High Cycle Fatigue of Ti-6Al-4V

In this study, a series of experimental studies was conducted to investigate the fatigue behavior of Ti-6Al-4V alloy at room temperature. Specifically, by inspecting the cylindrical specimens with a circumferential notch of different depths (20-200µm) and notch root radii (20-100µm), the notch effect was systematically investigated with tension-compression fatigue tests (R = –1). To quantify the effects of small notch, the -parameter model was adopted and its applicability for Ti-6Al-4V alloy was examined. Finally, the fatigue characteristics are discussed in conjunction with the behavior of small fatigue cracks at notches.