PSI - Issue 68

Robert Basan et al. / Procedia Structural Integrity 68 (2025) 782–787 R. Basan et al. / Structural Integrity Procedia 00 (2025) 000–000

784

3

• Modified Park-Song’s method for aluminum alloys (wrought) with 120 Nmm -2 < R ! # " = $ ! . % //+ &2 & ) ' " # 0123 ($,!* *%#&$&!' 4 + 5,*++×-( "( $ !+,,-(. % .-,7,( &2 & ) '(,,,- , • FKM Method for aluminum alloys (wrought) with 216 Nmm -2 < R m < 649 Nmm -2 :

m < 650 Nmm

-2 :

(3)

! # " =9,12 $ !(,.*, % &2 & ) '(,-(, + 0,895 8'-,-5/ &2 & ) '(,5/ .

(4)

3. Evaluation methodology and criteria For evaluation of the accuracy of individual methods, quantitative criteria proposed by Park and Song (1995) were used here: error criterion i.e. fraction of data points within a scatter band with factor of 3, E f (3), goodness of fit between the predicted and experimental values for individual datasets, ( E a ) Dset , goodness of fit between the predicted and experimental values for all data points, ( E a ) total and the average value of the above three parameters, Ē . The same criteria were used also in earlier studies by J ��� a � d S �� g ( 2002) a � d L �� a � d S �� g ( 2006) a � d m � r � r � c ��� l � b � Basan and Marohnić (2024) in a comprehensive study focused on estimation methods for steels. In order to obtain more detailed insight into the suitability and performance of individual methods, the modified evaluation methodology proposed by Basan and Marohnić (2024) is used here as well. Accordingly, separate evaluations are performed to determine the accuracy of estimation for materials divided into low strength and high strength subgroups in low-cycle fatigue (2 N f,exp ≤ 2 × 10 4 ) and high-cycle fatigue regime (2 N f,exp > 2 × 10 4 ). Division criteria regarding ultimate tensile strength are determined for each material group individually. Such separate evaluations help prevent averaging of results and tend to produce more detailed information. 4. Material data and analysis For mentioned analyses and evaluations, 27 aluminum and 13 titanium datasets were assembled using detailed experimental material data on aluminum and titanium alloys published in relevant literature. These are a subset of material data used in earlier study of strain-life fatigue parameters and behavior of different groups of metallic materials by Basan et al. (2011). All materials were reportedly tested in strain-control in air at room temperature at minimum 4 different load levels and with at least 0,4% range of total strain amplitude. Tensile strengths R m of both groups cover rather wide ranges of values with aluminum alloys having R m = 73...580 MPa and titanium alloys having R m = 434...1236 MPa. Material datasets for both groups were further subdivided into two strength subgroups as follows: • aluminum alloys:

13 materials datasets with R m < 400 MPa were designated as low strength (LS) 14 materials datasets with R m > 400 MPa were designated as high strength (HS) • titanium alloys: 7 materials datasets with R m < 900 MPa were designated as low strength (LS) 6 materials datasets with R m > 900 MPa were designated as high strength (HS)

Experimental numbers of load reversals to crack initiation 2 N f,exp were calculated for all considered materials for 8 different values of total strain amplitudes D e /2: 0,25 %, 0,3 %, 0,35 %, 0,4 %, 0,45 %, 0,5 %, 0,9 % and 1,5 %, using original Basquin-Coffin-Manson equation with experimentally obtained fatigue parameters. Estimated numbers of load reversals to crack initiation 2 N f,est were calculated using expressions (1-4), respectively. Fatigue lives pairs with unrealistically high values of load reversals 2 N f,exp (higher than 5·10 6 ) were excluded from the analysis. Remaining fatigue lives pairs (2 N f,exp ; 2 N f,est ) were then divided into low–cycle fatigue (LCF) subgroup with 2 N f,exp £ 20000 and high–cycle fatigue (HCF) subgroup with 2 N f,exp > 20000.