Fiber Bragg Gratings Based Cyclic Strain Measuring of Weld Toes of Cruciform Joints

Abstract

The real weld toe geometry is generally not mathematically perfect, resulting in obvious stress concentration effects, both on the weld section and along the longitudinal direction of the weld toe. The true stress-strain state at the local weld toe directly affects the fatigue performance and behavior of the welded structure. Therefore, a Fiber Bragg Grating (FBG) sensor based method for testing the cyclic strain at the weld toe was proposed. Cruciform welded joints were fabricated as specimens on which FBG sensors were arranged at several characteristic points along the weld toe curve. Strains at all the characteristic points under cyclic tensile load were measured and recorded, which showed the proposed measuring method could accurately obtain the complete local strain time histories along the weld toe. The strain time histories clearly reflected the cyclic hardening phenomenon in the early stage and the plastic yielding phenomenon in the final stage. Furthermore, based on the cyclic stress-strain constitutive model of the weld material, the stress-strain response curves of all the characteristic points were drawn. Combined with the fatigue fracture morphology, the mechanism of the unsynchronized initiation of the multiple cracks in the weld toe was investigated.

Parametric Formula for Stress Concentration Factor of Fillet Weld Joints with Spline Bead Profile

“…On the other hand, the accuracy of the estimation of the SCF with the photo-elastic method remains to be improved. In recent years, some new technologies, such as the fiber Bragg gratings [ 12 ], have been applied to assess the stress concentration in fatigue experiments with promising results. A wider diffusion of these new technologies is expected in the future.…”

Laser Welding on Cerclage Wire Joining in Femur Surgery

“…In the metal welding process, two or more pieces of metal welded together to form a welded joint which consists of base metal, weld metal, fusion zone and heat affected zone [15,21]. The welding process at the joint is a series of complicated processes such as local heating, metal melting and solidification, therefore, the welded joint is a region with heterogeneous ingredients, organization and mechanical properties [22,23]. The properties of the welding joint are affected by the process parameters of the laser welding such as frequency, beam power, focal length, defocus, spot size, welding beam speed, and shielding gas flow [24].…”