Ultra Low-Cycle Fatigue Behavior Comparison between Additively Manufactured and Rolled 17-4 PH (AISI 630) Stainless Steels

David Gonzalez-Nino,Timothy Strasser,Gary S. Prinz

doi:10.3390/met11111726

David Gonzalez-Nino, Timothy Strasser + Show 1 more

Open Access

https://doi.org/10.3390/met11111726

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Journal: Metals	Publication Date: Oct 28, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: University of Arkansas at Fayetteville

Abstract

This study investigates the mechanical behavior of additively manufactured (AM) 17-4 PH (AISI 630) stainless steels and compares their behavior to traditionally produced wrought counterparts. The goal of this study is to understand the key parameters influencing AM 17-4 PH steel fatigue life under ULCF conditions and to develop simple predictive models for fatigue-life estimation in AM 17-4 steel components. In this study, both AM and traditionally produced (wrought) material samples are fatigue tested under fully reversed (R = −1) strain controlled (2–4% strain) loading and characterized using micro-hardness, x-ray diffraction, and fractography methods. Results indicate decreased fatigue life for AM specimens as compared to wrought 17-4 PH specimens due to fabrication porosity and un-melted particle defect regions which provide a mechanism for internal fracture initiation. Heat treatment processes performed in this work, to both the AM and wrought specimens, had no observable effect on ULCF behavior. Result comparisons with an existing fatigue prediction model (the Coffin–Manson universal slopes equation) demonstrated consistent over-prediction of fatigue life at applied strain amplitudes greater than 3%, likely due to inherent AM fabrication defects. An alternative empirical ULCF capacity equation is proposed herein to aid future fatigue estimations in AM 17-4 PH stainless steel components.

Highlights

Current approaches to the seismic resistant design of steel structures rely on ductile energy dissipation mechanisms that are only optimized at a crude level due to the economics and limitations of traditional fabrication technologies
While some research on the mechanical behavior of Additive manufacturing (AM) metal parts under monotonic loading, high-cycle fatigue (HCF) and low-cycle fatigue (LCF) have been conducted [2,9,10,11,12,13], little is understood about the mechanical performance under ultra low-cycle fatigue (ULCF)
selective laser melting (SLM) AM processes with traditionally material fabrication processes

Summary

Introduction

Current approaches to the seismic resistant design of steel structures rely on ductile energy dissipation mechanisms that are only optimized at a crude level due to the economics and limitations of traditional fabrication technologies (e.g., eccentrically braced frame links, reduced beam-section moment connections, etc.). Researchers often seek better control and optimization within these ductile mechanisms to improve global seismic performance and create economic savings throughout the structural system. While some research on the mechanical behavior of AM metal parts under monotonic loading, high-cycle fatigue (HCF) and low-cycle fatigue (LCF) have been conducted [2,9,10,11,12,13], little is understood about the mechanical performance under ultra low-cycle fatigue (ULCF)

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