Issue 24

A. A. Shanyavskiy, Frattura ed Integrità Strutturale, 24 (2013) 13-25 ; DOI: 10.3221/IGF-ESIS.24.03 16 cracks were removed and some of them used in the present investigation. The disks with cracks that were selected for their fracture surfaces investigation and failed disks are described in Tab. 1. Test procedure Two of in-service cracked disks with small cracks were not subjected to crack opening and selected for their testing on the special bench-test. It was reproduced in-service acting stress-state with maximum stress level in accordance with maximum disks rotation speed in flight. During fatigue tests, in disks crack propagation was registered by the non- destructive day-penetrate periodical inspections. №№ Time since new, flights/hours n 1 n 2 с i , mm Comments 1 1329/3097 11 18 0.2–1.05 In-service discovered crack 2 1335/3658 8 9 1.5 - “ - 3 1421/3962 11 8 0.05–1.65 - “ - 4 1499/3733 1 8 2.0 - “ - 5 1690/5780 11 2 0.6 - “ - 6 2049/4688 4 13 0.1–0.5 - “ - 7 3121/6609 12 9 1.2 - “ - 8 2048/5994 + 561/2000 bench runs 8 1 4.0 In-service discovered crack; bench tests added 9 3079/5990 + 36 programmed runs 12 12 2.8 - “ - 10 2619/6345 - - - Broken in service 11 2696/5382 - - - Broken in service Table 1 : In-service operation time of NK8-2u engines, numbers n 1 of the holes (see schema of the Fig.1) with cracks and n 2 of cracks in holes and crack size as measured by the hole-surfaces. In one disks (P-3), it was realized block of 42 cyclic loads, reflecting in-service operated stress range during engine working, with constant stress amplitude and R-ratio near 0.4 between two neighbored disks cycling with one cycle at R=0. There were reproduced 50 blocks in disks fatigue tests. Maximum of stress level was reproduced for in-flight operated engine. In another disk (P-4), it was used engine with reproducing for disk in-service loading by the cyclically-equivalent-program (CEP). This program used for estimating design service goal for in-service disks [12, 13]. Fractographic analyses All selected disks were subjected to fractographic investigation on the scanning electron microscope EVO40 of the Karl Zeiss Company. Fracture surface patterns were used to reproduce in-service crack propagation in number of flights based on fatigue striations or beach mark number in accordance with developed earlier methodology [4, 6]. I NVESTIGATION RESULTS General trends of crack growth revealed by the broken disks -1 disk broke in service by cracking in three radial sections arranged at 120  angles to one another (see Fig. 2). These sections passed holes through that the disk was bolted to the engine shaft. In P-2 disk these angles were 150  , 120  , and 90  . Having matched the disk fracture surfaces, we saw the fracture to first initiate in one radial P