Materials Science and Engineering A 528 (2011) 6146–6156 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Mechanical reliability characterization of low carbon steel brazed joints with copper filler metal Morvarid K. Ghovanlou ∗ , Hamid Jahed, Amir Khajepour Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada article info Article history: Received 5 January 2011 Received in revised form 3 April 2011 Accepted 17 April 2011 Available online 28 April 2011 Keywords: Brazed joint Strength evaluation Fracture toughness Finite element modeling Failure mechanism abstract In this paper, mechanical reliability of low carbon steel brazed joints with copper as the filler metal is investigated. Tensile and shear strengths of the joint are evaluated by tension and torsion tests performed on butt-brazed joint specimens. Brazed joint failure under mixed mode loading is evaluated by biaxial tension–torsion tests as well. It is shown that a power law mixed mode failure criterion based on the single mode tensile and shear strengths well predicts the biaxial failure of the brazed joint. Furthermore, tensile, torsion, and biaxial tests are numerically simulated using ABAQUS software. Applying the exper- imentally measured deformations to the FE model the joint strengths are well estimated. Resistance of the brazed joint against crack propagation is evaluated by fracture toughness testing on SENB and SENT specimens. Crack extension is monitored using a video-microscope camera during the fracture test. The obtained fracture toughness values show dependency on the loading configurations applied to the speci- mens. SEM images of the joint fracture surfaces show two different failure mechanisms of dimple rupture and dendritic failure on the fracture specimens failed under tensile stresses. The EDS chemical analysis on the fracture surface of the tensile specimens reveals that MnS-rich dendrites are the source of den- dritic failure, while the finer Fe-rich dendrites and microvoids cause the dimple rupture. Dimple rupture initiated from dendrites and microvoids is the only failure mechanism observed on the fracture surface of the torsion specimens failed under shear stresses. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Brazing, as a type of welding process, is widely used in industry to manufacture assembled products from two or more individual parts. In the brazing process a filler metal in the form of foil, wire, paste, plating, or powder with a melting point of above 450 ◦ C and below the solidus temperature of the base metal is melted and dis- tributed between the faying surfaces of the individual parts to join them following solidification [1]. As compared to the fusion weld- ing, brazing technique produces less thermal distortion due to the uniform heating of components to the brazing temperature. Fur- thermore, preservation of physical and mechanical properties of base materials, reduction of induced residual stresses during join- ing, more uniform distribution of applied loads over a larger joint area, and feasibility of producing joints with high precision are among the advantages of brazed joints over weldments which have made this technique interesting in engineering applications [2]. Structural reliability of a brazed assembly is strongly depen- dent on the joint mechanical properties. Mechanical reliability of ∗ Corresponding author. Tel.: +1 519 888 4567x33646; fax: +1 519 885 58623. E-mail addresses: mkarimig@uwaterloo.ca (M.K. Ghovanlou), hjahed@uwaterloo.ca (H. Jahed), a.khajepour@uwaterloo.ca (A. Khajepour). brazed joints has been characterized by various criteria such as strength and toughness [3]. Effect of brazing temperature, heat- ing rate, holding time, and cooling process on the joint strength and ductility have been experimentally investigated for a wide range of brazed materials [4–8]. Yu and Lai [4] studied the effects of gap filler and brazing temperature on fracture of brazed joint. They found that increasing brazing temperature as well as addi- tion of gap filler at elevated temperatures improves joint strength and ductility. Chen and Chin [5] investigated the influence of braz- ing hold time on tensile and fatigue strength of brazed joints. It was observed that a shorter brazing cycle reduces diffusion reac- tion and the corresponding brittleness at the joint interface which yields more ductility and strength. Nayeb-Hashemi and Lockwood [6] showed that increasing the brazing time increases the amount of shrinkage porosities in the diffusion layer which reduces the joint strength, remarkably. Paiva et al. [7] and Feng et al. [8] investi- gated the effect of different brazing parameters such as hold time, temperature and filler metal on microstructure and mechanical properties of metal/ceramic joints to enhanced joint shear strength. Effects of joint clearance, different filler metals, and the correspond- ing microstructure on joint strength have also been investigated [9–12]. Nishi and Kikuchi [9] found out that the brazing filler metal has a significant effect on the joint strength as compared to that of the joint clearance and brazing hold time. They further observed 0921-5093/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2011.04.070