Abstract
Hole expansion ratio is a material parameter which defines the extent to which sheet metals are formed. Research has shown that, the stress state observed at the hole edge after hole expansion test is similar to those observed during conventional uniaxial tensile test. However, conventional tensile test methods are not efficient in evaluating material edge formability. This work utilised optical non-contact measuring techniques to examine failure behaviour during tensile test and hole expansion test of commercially pure titanium sheet, fabricated with either abrasive water jet cutting or electric discharge machining. The work found that, the deformation mode in conventional tensile testing are governed by localised necking and subsequently diffused necking prior to failure. Deformation mode observed in hole expansion test is characterised by localised necking with no visible occurrence of diffused necking prior to failure. The highest strains are concentrated at the hole edge during hole expansion test due to their sensitivity to the hole preparation method with accompanying multiple localised necking sites resulting in non-uniform deformation. Strains become concentrated in the bulk material microstructure rather than the machined edge during tensile testing resulting in single localised deformation site and a more homogenous deformation.
Highlights
Titanium and its alloys have been utilized in various applications mainly due to their high corrosion resistance, high fatigue toughness and high temperature strength [1]
Machining induced physiochemical functions are associated with the machined surface integrity properties, which affects the functional performance of components and potentially affect their manufacturing process [4]
Electric discharge machining (EDM) and Abrasive water jet (AWJ) cutting are non-traditional cutting techniques adopted by industry mainly due to their better surface finish and versatility compared to their conventional counterparts [11]
Summary
Titanium and its alloys have been utilized in various applications mainly due to their high corrosion resistance, high fatigue toughness and high temperature strength [1]. One of the downsides of this material is their poor machinability, which has been attributed mainly to their low thermal conductivity, high temperature strength and low elastic modulus [2]. Machining induced physiochemical functions are associated with the machined surface integrity properties, which affects the functional performance of components and potentially affect their manufacturing process [4]. Electric discharge machining (EDM) and Abrasive water jet (AWJ) cutting are non-traditional cutting techniques adopted by industry mainly due to their better surface finish and versatility compared to their conventional counterparts [11]. Severity of defects generated on edge surfaces during machining have many impacts on the in-service performance of titanium and its alloy. Considering the sensitivity of titanium to notches and surface inhomogeneity, there is the need to ascertain if the edge surface asperities produced during machining impacts on their forming behavior
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