Recent Advances in Structural Integrity Analysis - Proceedings of the International Congress

603 Pages·2015·168.996 MB·English

by  Lin Ye

Recent Advances in Structural Integrity Analysis:
Proceedings of the International Congress
(APCF/SIF-2014)
Recent Advances in Structural Integrity Analysis:
Proceedings of the International Congress
(APCF/SIF-2014)
Darlington Campus, University of Sydney, Australia
December 9 -12, 2014
The APCF/SIF-2014 Congress uniting:
Asian-Pacific Conference on Fracture and Strength (APCFS-2014)
International Conference on Structural Integrity and Failure (SIF-2014)
Hosted by:
The University of Sydney
Co-organised by:
Australia Fracture Group (AFG)
Chinese Mechanical Engineering Society Materials Institution (CMES-MI)
Korean Society of Mechanical Engineers, Materials and Fracture Division (KSME-MFD)
The Japanese Society of Mechanical Engineers, Materials and Mechanics Division (JSME-MMD)
AMSTERDAM (cid:2)BOSTON (cid:2)CAMBRIDGE (cid:2)HEIDELBERG (cid:2)LONDON
NEW YORK (cid:2)OXFORD (cid:2)PARIS (cid:2)SAN DIEGO
SAN FRANCISCO (cid:2)SINGAPORE (cid:2)SYDNEY (cid:2)TOKYO
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APCFS/SIF-2014 CONGRESS CHAIRS AND COMMITTEES

Congress Chairs
Ye L The University of Sydney
Kotousov A The University of Adelaide
Tu ST East China University of Science and Technology
International Organising Committee
Tu ST East China University of Science and Technology
Hayashi M Ibaraki Prefectural Government, Japan
Kim YJ Korea University
Kishimoto K Tokyo Institute of Technology
Ye L The University of Sydney
Local Organising Committee
Ye L The University of Sydney
Chang L The University of Sydney
Deng S The University of Sydney
Liu HY The University of Sydney
Tang Y Flinders University
Lu Y Monash University
Wang HJ The University of Sydney
Ghazali H The University of Sydney
Tabassum M The University of Sydney
Kalhori H The University of Sydney
Cheng X The University of Sydney
Zhang J The University of Sydney
Amir AN The University of Sydney
International Advisory Committee
Akiniwa Y Yokohama National University
Ben Jar PY The University of Alberta
Carpintery A The University of Parma
Chen CQ Tsinghua University
Chen W Xiamen University of Technology
Branco R Polytechnic Institute of Coimbra
Friedrich K The Technical University of Kaiserslautern
Han E Institute of Metal Research, Chinese Academy of Sciences
Hu J Shanghai Research Institute of Materials
Hutař P Institute of Physics of Materials, Academy of Sciences of the Czech
Republic
Inoue H Tokyo Institute of Technology
Jones R Monash University
Karger-Kocsis J Budapest University of Technology and Economics
Karihaloo BL Cardiff University
Kawakami T Toyama Prefectural University
Kinloch AJ Imperial College of London
Kishimoto K Tokyo Institute of Technology
Komotori J Keio University
Lazzarin P * Padua University
Li RKY The City University of Hong Kong
Lurie S Russian Academy of Sciences
Ma M China Automotive Engineering Research Institute
Mai YW The University of Sydney
Miura H Tohoku University
Navarro Al The University of Seville
* As this book was going to press, the organizers received the sad news of the death of Professor Paolo Lazzarin
Okazaki M Nagaoka University of Technology
Rose F DSTO, Australia
Sakagami T Kobe University
Shi H Tsinghua University
Sugeta A Hiroshima University
Sun J Xi’an Jiaotong University
Takahashi J The University of Tokyo
Wang C RMIT University
Wang TJ Xi’an Jiaotong University
Williams G Imperial College of London
Wu JS Hong Kong University of Science & Technology
Yoshikawa N The University of Tokyo
Yosibash Z Ben-Gurion University of Negev
Zhen L Harbin Institute of Technology
Zhou, L Hong Kong Polytechnic University
Technical Committee
Arai M Nagoya University
Baba H IHI Corporation
Biwa S Kyoto University
Chen X Tianjin University
Das R CSIRO, Australia
Ding H Wuhan University
Dyskin A The University of Western Australia
He Y Air Force Engineering University, P.R. China
Ho SY DSTO, Australia
Hirakata H Osaka University
Hu XZ The University of Western Australia
Inaba K Tokyo Institute of Technology
Iwasaki T Hitachi, Ltd
Izumi S The University of Tokyo
Kim HS The University of Newcastle
Li JC The University of Technology, Sydney
Li L Hunan University
Ma J The University of South Australia
Mizutani Y Tokyo Institute of Technology
Notomi M Meiji University
Ogawa T Aoyama Gakuin University
Pasternak E The University of Western Australia
Shibutani T Yokohama National University
Sumigawa T Kyoto University
Takano N Keio University
Tran B ASC, Australia
Uematsu Y Gifu University
Umeno Y The University of Tokyo
Wang L Northeastern University, China
Wang ZD East China University of Science and Technology
Wu Y Hefei University of Technology
Xiong W Huazhong University of Science and Technology
Yan C Queensland University of Technology
Yan W Monash University
Yang C The University of Western Sydney
Yang J Inner Mongolia University of Science & Technology
Yang X Beihang University
Yoneyama S Aoyama Gakuin University
Zhang S ADFA, The University of New South Wales
Zhang X East China University of Science & Technology
Zhao J Dalian University of Technology
FOREWORD

This book is a compendium of papers submitted and presented at the APCF/SIF-2014
Congress held in Sydney, Australia from 9 to 12 December 2014. All papers have been
peer-reviewed by the experts in the relevant areas. The APCF/SIF-2014 Congress united
the Asian-Pacific Conference on Fracture and Strength 2014 (APCFS-2014) and the
International Conference on Structural Integrity and Failure (SIF-2014). The Congress
was aimed to provide a unique opportunity for academics, engineers and postgraduate
students to meet, present and discuss the latest research developments, challenges and
trends in structural integrity.

Structural integrity is a key issue in the aerospace, power generation, transport, marine
and many other industries. Structural integrity evaluation is based on fundamental
understanding of failure mechanisms such as fracture, fatigue, creep, buckling,
corrosion, etc. It largely relies on advances in damage growth modelling, strength
prediction, defect detection and structural health monitoring techniques. The book
contains 117 papers, covering key aspects of structural integrity problems with a
particular emphasis on the characterisation of complex mechanisms of fracture, fatigue
and creep, structure-property relationship, multi-scale modelling and the development
of more accurate technologies for structural damage evaluation.

The Congress was hosted by The University of Sydney and co-organized by Australia
Fracture Group (AFG), the Chinese Mechanical Engineering Society, Materials Institution
(CMES-MI), the Korean Society of Mechanical Engineers, Materials and Fracture Division
(KSME-MFD) and The Japanese Society of Mechanical Engineers, Materials and
Mechanics Division (JSME-MMD). The Congress followed the series of the previous very
successful APCF and SIF international forums, in particular, APCFS 2012, Busan and the
8th SIF, Melbourne, 2013.

The book is the result of contributions from many researchers from different
laboratories, universities and research institutions. The Editors wish to express their
most grateful thanks to all authors of papers included in the book. Further, the Editors
wish to thank many of their colleagues for their kind support and help, including
Hayashi M, Johnston A, Kim YJ, Kishimoto K, Mai YW, Rose F, Tu ST, and Wang C.

Finally, the Editors wish to thank Deng S (The University of Sydney) and Sue Gruzelier
who provided great help in receiving, compiling and editing of the papers and the
associated publication agreements; without their assistance, this publication of the Book
would not be possible.

Ye L (The University of Sydney)
Kotousov A (The University of Adelaide)
Chang L (The University of Sydney)

1
Optimization and fracture mechanism analysis of
TC17 titanium alloy simulated-blade with two-sided
laser shock processing

X. Nie, Y. Li, W. He, L. Zhou
Science and Technology on Plasma Dynamics Laboratory,
Air Force Engineering University, P.R. China

ABSTRACT

Laser shock processing (LSP) is an innovative surface treatment technology, which can
effectively improve the fatigue performance of metals. In order to apply this technology
on aero-engine compressor blade to improve its fatigue resistance, a TC17 titanium alloy
simulated-blade was designed and trested by LSP. According to the finite element
analysis and fatigue test results, the LSP procedure was optimized. And the fatigue
strength was effectively improved by the optimized LSP procedure, compared to the
first LSP procedure. The fracture mechanisms of fatigue crack initiation and growth with
different LSP procedures were incestigated and compared.

1. INTRODUCTION

Laser shock processing (LSP) is an innovative surface treatment technology, which can
improve the fatigue resistance of metals and alloys (1). Compared with conventional
shot peening (SP), LSP has some special advantages, such as deeper compressive
residual stress, small cold work rate, lower surface roughness and better controllability.
Beacause of the above advantages, it becomes more and more popular in the surface
treatment field. What’s more, LSP has been successfully applied on fan/compressor
blades of military aero-engines to improve HCF performance and foreign object damage
resistance. Many studies have been carried out to discuss the effects of LSP on fatigue
property for different metals and alloys (2,3). And some reseaches focused on the effects
on the fatigue crack initiation and growth (4-6). In our previous work, LSP was
successfully applied on some titanium alloys to improve the fatigue strength, and the
strengthening mechanism was also discussed(7,8).

However, the above experimental studies just investigated the effects of a specified LSP
procedure, always with a simple laser-peened path, on the fatigue performance. But
there were few experimental studies about the effects of different LSP procedures
including laser parameters and laser shocked-path. In this paper, LSP procedure for
TC17 simulated-blade was optimized according to the work stress state. And the
simulated-blades were treated with two LSP procedures. The fatigue limits with
different LSP procedures were compared by the up-and-down method during fatigue
tests. The fracture mechanisms of fatigue crack initiation and growth with different LSP
procedures were compared.

_________________________________________
© The author(s) and/or their employer(s), 2014
2
2. EXPERIMENTAL PROCEDURE

2.1 Laser shock processing
The LSP process utilizes laser pulse irradiated at the target surface covered by opaque
ablating layer and transparent confining layer. When the laser beam passes through the
transparent layer and strikes the surface, the ablating layer absorbs the laser and
immediately vaporized into the plasma. The rapidly expanding plasma leads to the
formation of shock wave which strikes the material and propagates into the material
with an intensity of several GPa. If the shock pressure is greater than the dynamic field
strength, plastic deformation will be generated with compressive residual stress and
microstructure changes in the surface. Because of the symmetrical structure, the
simulated-blades were treated by two-sided LSP shown in reference (7).

2.2 Material and specimen
TC17 titanium alloy is widely used in Chinese aviation field, such as aero-engine fan and
compressor blade. In order to simulate the work stress state of aero-engine compressor
blade, the TC17 titanium alloy specimen was designed and machined into the special
structure, namely simulated-blade shown in Fig.1(a). The simulated-blades were
machined by Gas-turbine research institute of China. Fig.1(b),(c) is the first-order modal
displacement contour and equivalent effective stress contour by finite element analysis
(FEM). The first-order modal is a cantilever vibration modal. The greatest vibration
amplitude locates at the blade-tip. The calculated first-order frequence is 338 HZ, which
is well consistent with the factual resonance frequence in vibratory fatigue tests,
332HZ~345HZ. In addition, the maxiam vibration stress locates at the blade-root
rounding near the R transition line, especially the center region. In response to the
stress analysis results, the LSP region was confirmed as the blade-root rounding area,
the dashed region in Fig.2(a), which is 30 mm×14.4 mm.

Fig.1 Schematic diagram and first-order modal of simulated-blade
3
3. RESULTS AND DISCUSSION

3.1 LSP procedure optimization and fatigue performance
The simple snaky laser shocked-path was applied in first LSP procedure (Fig.2(a)) with
detailed laser parameters as following: laser energy/6J, laser duration/20ns, laser spot
diameter/3mm, laser fluence/4.24GW/cm2, overlapping rate/50%, 1 impact. Fifteen
simulated-blades were treated by LSP. After LSP, thirty simulated-blades without and
with LSP were used to conduct vibration fatigue tests on D-300-3 electric vibration
system shown in reference (7). In the fatigue test, the test stress was measured by a
strain gage which is sticked on the simulated-blade root with highest work stress as
shown in Fig.1(c). At the same time, the amplitude of simulated-blade tip in the fatigue
test was measured by a laser displacement sensor. Then, the relataionship between the
highest work stress and amplitude of simulated-blade tip was established. And we just
monitored the amplitude of simulated-blade tip in test. The fatigue test results were
processed by the fatigue up-and-down method.

The original fatigue limit of TC17 titanium alloy simulated-blade is 405.7MPa. However,
the fatigue limit with first procedure is only 360MPa, decreased by 11.3%. According to
the fluorescent test results, it is found that the fatigue crack initiates at the blade edge
within the LSP region, far from the blade-root rounding. In order to analyze the the
cause of the fatigue crack initiation, a numerical simulation work of the first LSP
procedure was conducted. The simulation results indicate that the maximal equivalent
effective plastic strain locates at blade edge, where there is a material protrusion
resulted from the accumulated plastic deformation. The accumulated plastic
deformation may result in the complicated residual stress field generated. Even more,
tensile residual stresses may be generated in the material protrusion area, which leads
to fatigue crack initiation. Thus, the main cause of fatigue crack initiation is not the
vibration stress, and it may be induced by the unbenefited residual stresses.

According to the cause of the fatigue performance deterioration with the first LSP
procedure, the LSP procedure was optimized as shown in Fig.2(b). In order to advoid the
accumulated plastic deformation generated at blade edge, the center region undergone
great work stress was designed to be laser peened with a great intensity, but with a low
intensity for the simulated-blade edge region. The design target is to induce greater
residual compressive stresses in the center region and reduce the accumulated plastic
strain at the blade edge. In the previous research work, it is found that there is direct
relationship between the laser fluence and laser induced plastic deformation. The
greater laser fluence is, the greater plastic deformation induced by LSP is. Therefore, an
optimized distinctive LSP procedure was confirmed with four LSP regions, region 1
(3J/20ns/Φ2.4mm/50%/1 impact) with high laser fluence (3.32GW/cm2) and region
2/3/4 (2J/20ns/Φ2.4mm/50%/1 impact) with low laser fluence (2.21GW/cm2). And
the treatment sequence is region 1 first, then region 2, region 3 and region 4. The great
compressive residual stresses are produced in region 1 for the resistance to the greatest
work stress. And lower compressive stresses are generated in region 2/3/4 for the
transition of great compressive stresses in region 1, preventing stress concentration.
Fifteen simulated-blades treated with the optimized LSP procedure were used to
conduct fatigue tests. The fatigue limit with the optimized LSP procedure is 462.9MPa,
14.1% incresed by compared with the orginal fatigue limit. And the fatigue crack
initiates at the center region, not the blade edge. In summary, the first LSP procedure can
induce great compressive stresses in the LSP region, but with great accumulated plastic
deformation, even tensile residual stress at blade edge resulting in fatigue cracking. In
contrast, the optimized LSP procedure can induce great compressive stresses in region 1
4
and realize the gradual transition of the compressive stresses in region2/3/4, without
great accumulated plastic deformation generated at blade edge.

Fig.2 Two LSP procedures and laser shocked path of simulated-blade

3.2 Fracture mechanism analysis
The fractographys of simulated-blades treated by two LSP procedures were observed by
a JEOL/JSM-6360LV scanning electron microscope (SEM). Before the observation, the
raptured simulated-blades were cleaned with ethanol in the ultrasound cleaning
machine. Fig.3(a) is the typical fractography with first procedure. It shows that the
fatigue crack initiates at the blade edge and propogates into the center/depth. In the
period of fatigue crack initiation and transition, there are many cleavage planes, subtle
fatigue striations. There are many ridges in the fatigue crack growth region, but not very
orderly in Fig.3(b), which may be ascribed to the irreguar residual stress distribution.
Dense fatigue striations with secondary cracks are generated during fatigue crack
growth in Fig.3(c), which results from complicated residual stress state.

Fig.3 Typical fractography with the first LSP procedure

Differently, the fatigue crack initiates at the surface of simulated-blade center part near
the blade root rounding with optimized procedure (Fig.4(a)). The ridges are clearer with
layered distribution, and denser compared to that with first procedure (Fig.3(b)). It can
be concluded that more time of the fatigue crack initiation is needed. The fatigue crack
5