Session: CS-17-03 Fatigue Evaluation Method

Paper Number: 106814

106814 - Fatigue Property Evaluation of Metallic Am Parts and Determination of Design Stress Allowables 

   As additive manufacturing (AM) is being adopted for cost-effectively fabricating metallic parts for safety-critical components subjected to fatigue loading, one of the major challenges has been on how to address structural significance of spatially distributed geometric discontinuities. To address some of the issues for pressure equipment applications, a DOE project was initiated to develop a robust metal AM flaw assessment methodology, aiming to examine the feasibility of extracting fatigue design stress allowable.  This project was carried out in conjunction with ASME’s BPTCS/BNCS committee activities with test data both provided by some committee member organizations and resulted from a comprehensive literature search.  This paper highlights both the technical approach adopted and major findings to date, including:  

(1)    The master S-N curve (or E-N curve) method adopted by ASME BP&V Div 2 Code seems to provide an effective framework for extracting fatigue design stress allowable for fatigue evaluation for AM components

(2)    Recognizing inevitable presence of some level of microscopic geometric discontinuities both at part surface and interior, e.g., lack fusions, porosities, etc., fatigue test data show that as long as those discontinuities are within a controlled limit according to industry’s best practice, a consistent fatigue behavior in terms of master S-N curve or E-N curve and its scatter band can be established for extracting fatigue design allowable

(3)    The effects of post-processing conditions, e.g., as-manufactured versus machined/polished, shot-peened, HIP, stress-relieved, seem not significant, particularly in the low cycle fatigue regime. In high cycle fatigue regime, post-processing methods seem to show more noticeable effects on fatigue behaviors, but far less significant than wrought material fatigue test data

(4)    A cost-effective AM flaw acceptance criterion can be implemented by identifying fatigue-critical locations or hot spots as defined in this study for a set of four typical components. Fitness for Service (FFS) methodologies are shown effective in quantitatively establish flaw acceptance criteria for these hot spot locations.

Presenting Author: Pingsha Dong University of Michigan

Presenting Author Biography: Professor, Naval Architecture and Marine Engineering, University of Michigan

Authors:

Pingsha Dong University of Michigan
George Rawls GBR Consulting
Tim Krentz SAVANNAH RIVER NUCLEAR SOLUTIONS LLC