FINITELY SCOPED, HIGH RELIABILITY FATIGUE CRACK GROWTH MEASUREMENTS

2018 ◽  
Vol 91 (4) ◽  
pp. 644-650
Author(s):  
Joshua R. Goossens ◽  
William V. Mars
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
High Reliability ◽  
Time Budget ◽  
Rest Period ◽  
Operating Conditions ◽  
Test Time ◽  
Crack Growth Behavior ◽  
Strain Peak

ABSTRACT Classical procedures for characterizing fatigue crack growth behavior often suffer from uncertainties that make it difficult to plan for productive use of test instrument time, and that can result ultimately in too noisy measurements. An enhanced procedure has been implemented that is based on a fixed test time budget, and that establishes operating conditions that produce crack growth rates down to minimum measurable rates. The procedure features (1) a haversine pulse deformation test cycle followed by a rest period, (2) a strain peak that ramps linearly over time, (3) minimum and maximum limits on the strain peak chosen to avoid unproductive test time, and (4) a stress–strain probe cycle for purposes of observing strain energy density. A set of replicates of a carbon black filled, natural rubber bushing compound has been characterized via both procedures, and a statistical analysis is made to compare both. The new procedure significantly improves the quality of crack growth rate curve measurements.

scholarly journals Fatigue Crack Growth Behavior Evaluation of Grainex Mar-M 247 for NASA’s High Temperature, High Speed Turbine Seal Test Rig

2007 ◽  
Author(s):  
Irebert R. Delgado ◽  
Bruce M. Steinetz ◽  
Clare M. Rimnac ◽  
John J. Lewandowski
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Depth ◽  
Growth Behavior ◽  
Operating Conditions ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Inspection Interval ◽  
Bolt Holes

The fatigue crack growth behavior of Grainex Mar-M 247 is evaluated for NASA’s Turbine Seal Test Facility. The facility is used to test air-to-air seals for use primarily in advanced jet engine applications. Because of extreme seal test conditions of temperature, pressure, and surface speeds, surface cracks may develop over time in the disk bolt holes. An inspection interval is developed to preclude catastrophic disk failure by using experimental fatigue crack growth data. By combining current fatigue crack growth results with previous fatigue strain-life experimental work an inspection interval is determined for the test disk. The fatigue crack growth life of the NASA disk bolt holes is found to be 367 cycles at a crack depth of 0.501 mm using a factor of 2 on life at maximum operating conditions. Combining this result with previous fatigue strain-life experimental work gives a total fatigue life of 1032 cycles at a crack depth of 0.501 mm. Eddy-current inspections are suggested starting at 665 cycles since eddy current thresholds are currently at 0.381 mm. Inspection intervals are recommended every 50 cycles at maximum operating conditions.

Computed Dependence of Rubber'S Fatigue Behavior on Strain Crystallization

2009 ◽  
Vol 82 (1) ◽  
pp. 51-61 ◽  
Author(s):  
W. V. Mars
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Operating Conditions ◽  
Fatigue Threshold ◽  
Crack Growth Behavior ◽  
Fatigue Crack Nucleation ◽  
Nucleation Behavior ◽  
Wide Range

Abstract This work explores the consequences of strain crystallization on rubber's fatigue crack nucleation behavior over an extensive space of operating conditions, including tension and compression loading states, and relaxing and non-relaxing cycles. The study considers, via computation, how the nonlinear elastic stress-strain behavior, the fatigue crack growth characteristics, and the damage accumulation law combine to produce the Haigh diagram and the Cadwell diagram. Four hypothetical materials are studied, which differ in their crystallization and associated fatigue crack growth behavior. The calculations demonstrate that a relatively simple idealization can credibly predict the unique shape and sensitivities of observed fatigue behavior over a wide range of conditions. They also clarify how features of the Haigh and Cadwell diagrams are linked to the occurrence of crystallization and to parameters such as the power-law slope and the fatigue threshold.

scholarly journals Fatigue Crack Growth Behavior Evaluation of Grainex Mar-M 247 for NASA’s High Temperature High Speed Turbine Seal Test Rig

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Irebert R. Delgado ◽  
Bruce M. Steinetz ◽  
Clare M. Rimnac ◽  
John J. Lewandowski
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Depth ◽  
Growth Behavior ◽  
Operating Conditions ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Inspection Interval ◽  
Bolt Holes

The fatigue crack growth behavior of Grainex Mar-M 247 is evaluated for NASA’s turbine seal test facility. The facility is used to test air-to-air seals primarily for use in advanced jet engine applications. Because of extreme seal test conditions of temperature, pressure, and surface speeds, surface cracks may develop over time in the disk bolt holes. An inspection interval is developed to preclude catastrophic disk failure by using experimental fatigue crack growth data. By combining current fatigue crack growth results with previous fatigue strain-life experimental work, an inspection interval is determined for the test disk. The fatigue crack growth life of NASA disk bolt holes is found to be 367cycles at a crack depth of 0.501mm using a factor of 2 on life at maximum operating conditions. Combining this result with previous fatigue strain-life experimental work gives a total fatigue life of 1032cycles at a crack depth of 0.501mm. Eddy-current inspections are suggested starting at 665cycles since eddy current detection thresholds are currently at 0.381mm. Inspection intervals are recommended every 50cycles when operated at maximum operating conditions.

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