Low Cost Corrosion Damage Mitigation and Improved Fatigue Performance of Low Plasticity Burnished 7075-T6

High cycle fatigue (HCF) performance of turbine engine components has been known for decades to benefit from compressive surface residual stresses introduced through shot peening. However, credit for the fatigue benefits of shot peening has not been taken into account in the design of components. Rather shot peening has been used primarily to safe guard against HCF damage initiation. Recently, laser shock processing (LSP) and low plasticity burnishing (LPB) have been shown to provide spectacular fatigue and damage tolerance improvement by introducing deep (through-thickness) compression in critical areas. Until now, the fatigue benefits of these new surface treatments have been introduced during repair to improve an existing design. The present paper describes a design methodology and testing protocol * to take appropriate credit for the introduction of beneficial residual stresses into a component design to achieve optimal fatigue performance.A detailed design protocol has been developed that relates the introduction of a residual stress distribution using LPB for targeted HCF performance. This design protocol is applied to feature specimens designed to simulate the fatigue conditions at the trailing edge of a 1 st stage low pressure compressor vane to provide optimal trailing edge damage tolerance. The use of finite element modeling, linear elastic fracture mechanics, and x-ray diffraction documentation of the residual stress field to develop LPB processing parameters is described. A novel adaptation of the traditional Haigh diagram to estimate the compressive residual stress magnitude and distribution to achieve optimal fatigue performance is described. Fatigue results on vane-edge feature samples are compared with analytical predictions provided by the design methodology. The potential for designing reduced section thickness of structural components leading to weight savings is discussed.

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“…ABSTRACT see report 15. SUBJECT TERMS service, no design credit for the beneficial compression is generally taken.…”

Section: Supplementary Notesmentioning

confidence: 99%

Introduction of Residual Stresses to Enhance Fatigue Performance in the Initial Design

́y

Jayaraman

Ravindranath

2004

Volume 2: Turbo Expo 2004

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“…SUBJECT TERMS 9 th National Turbine Engine High Cycle Fatigue Conference 2 fatigue damage. [17][18][19][20] The LPB process can be performed on conventional CNC machine tools at costs and speeds comparable to conventional machining operations such as surface milling. 17-4PH stainless steel 1 st stage compressor blades have blade edge FOD, corrosion pitting, and erosion damage which reduces fatigue life.…”

Section: Supplementary Notesmentioning

confidence: 99%

Mitigation of FOD and Corrosion Fatigue Damage in 17-4 PH Stainless Steel Compressor Blades With Surface Treatment

Prevéy¹,

Jayaraman²,

Ravindranath³

2004

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Compressor blades of a military aircraft turbine engine made of 17-4 PH stainless steel have been reported to have blade edge foreign object damage (FOD), corrosion pitting, and erosion damage that reduce fatigue life. This paper reports the findings of a comprehensive investigation of the effect of residual compressive stresses, imparted by various surface treatments, to improve leading edge damage tolerance and active corrosion fatigue performance in a salt water environment. Initial fatigue and corrosion fatigue tests were conducted in feature specimens designed to simulate the geometrical conditions of thick section and blade leading edges of compressor blades. The FOD tolerance and corrosion fatigue performance of 17-4PH prepared by low plasticity burnishing (LPB), shot peening (SP), and low stress grinding (LSG) were compared. LPB dramatically improved both high cycle fatigue ( HCF) and corrosion fatigue performance, providing tolerance of 0.040 in. deep FOD in thick section and 0.050 in. deep leading edge FOD. Shot peening afforded little benefit in the presence of FOD 0.010 in. deep. Fatigue initiation at relatively low applied stress levels originating from existing corrosion pits outside of the LPB treated zone limited the ability to test the surface treatments on actual fielded T56 blades retired from service. In the absence of prior pitting, LPB provided 0.020 in. deep FOD tolerance on new T56 blades. Both the damage tolerance and active corrosion fatigue performance of 17-4PH in salt water increased with the depth of the compressive zone produced.

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“…The refined surface layers in general show better corrosion resistance than their large grain counterparts. Prevey and co-workers [17,18] observed that low plasticity burnishing can provide a layer of compressive residual stress with sufficient depth to effectively increase the fatigue life of many materials. Hamadache et al [19] observed 89% wear improvement and up to 9% hardness improvement compared to the sample made by turning after roller burnishing of structural Rb40 steel.…”

Section: Introductionmentioning

confidence: 99%

Improvement of Surface Properties by Burnishing on Aluminium Alloy

Ramana¹,

Tjprc²

2018

IJMPERD

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Low Cost Corrosion Damage Mitigation and Improved Fatigue Performance of Low Plasticity Burnished 7075-T6

Cited by 57 publications

References 7 publications

Introduction of Residual Stresses to Enhance Fatigue Performance in the Initial Design

Introduction of Residual Stresses to Enhance Fatigue Performance in the Initial Design

Mitigation of FOD and Corrosion Fatigue Damage in 17-4 PH Stainless Steel Compressor Blades With Surface Treatment

Improvement of Surface Properties by Burnishing on Aluminium Alloy

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