Predicting the J integral fracture toughness of Al 6061 using the small punch test

Abstract

A B S T R A C TThe 6000 series aluminium alloys (Al-Mg-Si systems) are commonly used as mediumstrength structural materials; in particular, the 6061 (Al-1Mg-0.6Si) alloy is widely utilized as a general-purpose structural material due to its excellent formability and corrosionresisting capabilities. The objective of this study was to obtain a correlation between the small punch (SP) test estimated equivalent fracture strain (ε qf ) and fracture toughness (J 1C ) property for 6061 aluminium, and determine its viability as a non-destructive fracture toughness test technique for remaining life assessment of in-service components. Samples of 6061-T6 aluminium were cut from bulk plate, in both the longitudinal and transverse directions, for the as-received condition as well as subjected to three different over-ageing heat-treatment schedules. A strong linear correlation between valid J 1C and SP estimated biaxial fracture strain ε qf is presented for aluminium 6061 at room temperature.Keywords aluminium alloy 6061; equivalent fracture strain; in-service component; J integral fracture toughness; remaining life assessment; small punch test. N O M E N C L A T U R EF UPTHRUST = upthrust due to sample in water J 1C = valid J integral fracture toughness J 0 = material/environment dependent empirical constant k = material/environment dependent empirical constant m DRY = dry weight of aluminium m WET = wet weight of aluminium n = empirical parameter in small punch correlation R 2 = correlation coefficient for least squares curve fit t 0 = original thickness of small punch disk t = thickness of small punch disk at fracture T SP = transition temperature in small punch tests w CT = critical strain energy density of compact tension sample w SP = critical strain energy density of small punch sample x = material dependent characteristic averaging distance β = empirical parameter in small punch correlation δ = small punch deflection at fracture ε qf = equivalent biaxial strain at fracture ρ Al = density of aluminium ρ H2O = density of water

A study on rate sensitivity of elasto-plastic fracture toughness of TRIP steel evaluated by a small punch test

“…Figure 5 shows a comparison of load -deflection curves obtained in the present study and the previous study [6]. From this figure, both results show fairly good agreement.…”

“…To show validity of the manufactured SP testing apparatus, a quasi-static SP test using aluminum alloy 6061 is conducted at crosshead speed of 0.2 mm/min following the previous study [6]. Figure 5 shows a comparison of load -deflection curves obtained in the present study and the previous study [6].…”

An Energy Based Fatigue Life Prediction Framework for In-Service Structural Components

“…12(a) and (b), low and high magnification respectively. As continual straining of the material increases, the microvoids tend to grow, coalesce and eventually form an incessant fracture face [17,18]. Sample showed typical ductile failure occurred by formation of microvoids, void growth and finally coalescence.…”

Development of a new methodology for estimating the CTOD of structural steels using the small punch test

“…This consists of the measurement of the so-called biaxial strain at fracture, e qf , which relates the original specimen thickness, t, to the thickness measured in the failure zone, t f (expression 1). Several authors [2,5,9,[11][12][13][14] have found good relationships between this parameter and fracture toughness, although very different, totally empirical expressions have been obtained, showing a clear dependence on the type of material. Other reported strategies include the measurement of the energy furnished by the test until a 20% drop after the application of the maximum load [6,15] or the estimation of the parameters of an appropriate damage model by applying neural networks to the SPT result and subsequently simulating the mechanical behaviour of the standard fracture toughness test [16,17].…”