PSI - Issue 42

Robert Basan et al. / Procedia Structural Integrity 42 (2022) 655–662 R. Basan et al. / Structural Integrity Procedia 00 (2019) 000–000

658

4

individual estimation methods accuracy. This was confirmed in a preliminary study peerformed by Basan et al. (2015) of a few selected estimation methods using very compact and consistent dataset on a single low-alloy steel 42CrMo4 featuring different heat treatments. Significant differences which were determined in performance and accuracy of the reviewed estimation methods for low- and high-cycle fatigue lives and for two subgroups of materials regarding their ultimate strength. These findings were main motivation for this extended research of estimation methods and their suitability for various steel materials divided into unalloyed, low-alloy and high-alloy steel groups and then subdivided further into low strength and high strength subgroups which were then analyzed separately in low cycle and high cycle fatigue regime.

3. Methodology, data and analysis 3.1. Considered estimation methods

Research results presented in this paper are part of a wider study that as a whole, will include and consider a larger number of estimation methods. Since some methods require multiple monotonic properties and parameters some of which are not readily available, significant part of the preparatory work includes additional effort on completion of individual materials datasets. Therefore, the work presented here includes the results of the analysis and evaluation of estimation methods that were subject also of preliminary study done by Basan et al. (2015) and which require basic monotonic properties such as tensile strength, hardness and Young’s modulus: • Uniform Material Law for unalloyed and low–alloy steels, Bäumel and Seeger (1990): ( ) ( ) 0,58 f 0,087 f m 0,59 2 1,5 2 2 − − + Δ = N N E R ψ ε (5)

R

R

E R m 125 1,375 = − ψ for

1 = ψ for

0,003

0,003

where

and

m ≤

m ≥

E

E

• Hardness method for steels with Brinell hardness between 100 HB and 700 HB, Roessle and Fatemi (2000):

2

4,25

225 2

0,32

487

191000

E HB

HB

HB

Δ = ε

+

−

+

( ) f N

( ) 0,56 f 2 − N

0,09

−

(6)

+

2

E

• Median method for steels, Meggiolaro and Castro (2004):

R

Δ = ε

( ) f N

( ) 0,59 f − N

0,09

−

m 1,5 2

0,45 2

(7)

+

.

2

E

3.2. Material data and datasets preparation Material data used in present study originate from an earlier analysis of strain-life fatigue parameters and behaviour of different groups of metallic materials by Basan et al. (2011) consisting of total of 267 steel materials datasets of which 128 were unalloyed steels (UA), 64 were low-alloy steels (LA) and 75 were high-alloy steels (HA). In order to be considered viable for analysis, materials needed to be tested in strain-control at room temperature at minimum 4 different load levels and with at least 0,4% range of total strain amplitude. Values of tensile strength of selected materials cover rather wide ranges of ultimate tensile strength across all steel subgroups: unalloyed steels ( R m = 345...2360 MPa), low-alloy steels ( R m = 435...2240 MPa) and high-alloy steels ( R m = 440...2585 MPa).