The development of a novel technique for small ring specimen tensile testing

• Published in: Theoretical and applied fracture mechanics 2019-02, Vol.99, p.131-139
• Main Authors: Kazakeviciute, J., Rouse, J.P., De Focatiis, D.S.A., Hyde, C.J.
• Format: Article
• Language: English
• Subjects: Aluminium; Aluminum base alloys; Creep tests; Equivalence; Finite element analysis; Finite element method; Fracture toughness; Gas turbine engines; Material properties; Mathematical analysis; Modulus of elasticity; Sensitivity; Size effects; Small ring specimen; Standard data; Strain rate; Tensile testing; Turbine blades
• ISSN: 0167-8442; 1872-7638
• DOI: 10.1016/j.tafmec.2018.11.016

•A small ring specimen experimental procedure has been developed for tensile testing.•7175-T7153 wrought aluminium alloy has been applied to this new test technique.•Finite element techniques were used in the development of the new test technique.•A strain energy based analytical solution has also been developed.•Experimental data, analytical solution and FEA model are in good agreement. The wide scale use of small specimens in routine testing programs could significantly reduce material resource requirements (factors of 10 are easily achievable). This is a major benefit to situations where there is not enough material to manufacture conventional, full-size specimens, such as first-stage gas turbine blade roots. However, limitations exist due to concerns over size effects, manufacturing difficulties, uncertainties related to the application of representative loading conditions and complex interpretation procedures of non-standard data. Due to these limitations, small specimen testing techniques have been mostly applied in ranking exercises and to determine approximate or simple material parameters such as Young’s modulus, minimum creep strain rate and fracture toughness. The small ring method is a novel, high sensitivity small specimen technique for creep testing that has been extended in the present work to the determination of tensile material properties. The main advantages of the small ring specimen are that it is self-aligning and has a large equivalent gauge length in comparison to other small specimens, resulting in much higher testing sensitivity. In the present work, this specimen type mimics conventional, full-size, monotonic testing, allowing for observations of elastic and plastic material response to be made. Wrought aluminium alloy 7175-T7153 small rings were tested at room temperature at 5 different loading (displacement) rates and the results compared to conventional, full-size, monotonic specimen equivalents. Finite element analysis was conducted in order to evaluate the equivalent gauge section and equivalent gauge length in the small ring specimen (which varied between circa 0.35–1.4 mm2 and 25–45 mm, respectively) to facilitate these comparisons. An analytical solution has also been derived in order to validate the finite element analysis.