Issue 59

Yu. G. Matvienko et alii, Frattura ed Integrità Strutturale, 59 (2022) 115-128; DOI: 10.3221/IGF-ESIS.59.09

material flow in axial direction caused by the mandrel reaching maximum value at exit side. Thus, simultaneous evaluation of fracture mechanics parameters on two opposite sides of the specimen is of considerable interest with respect to quantifying damage accumulation. That is why deriving information, which concerns an evolution of fracture mechanics parameters, related to the narrow artificial notch emanating from cold-expanded hole in plane rectangular specimens under high-cycle fatigue on a basis of two-side measurements, is the second goal of this paper. S PECIMENS AND EXPERIMENTAL TECHNIQUE luminium alloy 1163T plane specimens of dimensions 200×70×10 mm with a centred through-thickness hole of nominal diameter 2 ଴ = 10.0 mm are used in the present research (Fig. 1a). Russian aluminium alloy1163T is analogous to AA2024 alloy. Mechanical properties of this alloy are the following: Young’s modulus E = 74,000 MPa, yield stress σ ୷ = 320 MPa and Poisson’s ratio = 0.33. All coupons were cut from a single 1200×800×15 mm plate by the same milling technology so that their longitudinal axes were aligned with the plate rolling direction. Full set of specimens includes 7 units. Pilot holes of 9.82 mm in diameter were drilled, followed by a 10.0 mm final reaming. The degree of cold expansion is 0.5%. Details of cold expansion technology are presented in Ref. [12]. Absence of residual stresses in all specimens has been established by data of probe hole drilling and further optical interferometric measurements of deformation response to local material removing [21]. Narrow artificial notches, emanating from the hole at different stages of high-cycle fatigue, serve to manifest a damage level. These notches are inserted without applying external load. A

a b Figure 1: Scheme of RSH specimens (a) and location of measurement points (b).

Specimen

RSH_3

RSH_4

RSH_5

RSH_6

RSH_7

RSH_1

Number of cycles, N

0 0

20000

40000

60000

80000

110000

Lifetime, %

18.2

36.4

54.6

72.7

100

Table 1: Nomenclature of T5-H1 specimens and fatigue loading program. The first specimen RSH_1 is used for lifetime estimation. The second specimen RSH_2 serves for a proper choice of the first and the second notch length proceeding from fringe resolution limit. The third specimen RSH_3 gives the characterization of residual stress before fatigue loading. Other specimens are subjected to uniaxial tension with stress range ∆ = 162 MPa and stress ratio R = 0.01. The fatigue tests were carried out with a load frequency of 3 Hz in MTS- 250 servo hydraulic testing machine. Fracture of the reference specimen occurs after number of cycles ி = 110000. Number of cycles for each investigated specimen is listed in Tab. 1. Ref. [12] includes a comprehensive description of two-side simultaneous measurements of in-plane displacement components relevant to the artificial notch by electronic

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