_STP_591-1976.pdf

RESISTANCE TO PLANE-STRESS FRACTURE(R-CURVE BEHAVIOR)OF A572 STRUCTURAL STEEL Presented at Eighth National Symposium on Fracture Mechanics,Brown University,Providence,R.I.,26-28 Aug.1974 ASTM SPECIAL TECHNICAL PUBLICATION 591 So R.Novak U.S.Steel Corporation Research Laboratory List price$5.25 04-591000-30 itTi AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street,Philadelphia,Pa.19103?9 BY AMERICAN SOCIETY FOR TESTING AND MATERIALS 1976 Library of Congress Catalog Card Number:75-18414 NOTE The Society is not responsible,as a body,for the statements and opinions advanced in this publication.Printed m New Carlisle,Ohio February 1976 Foreword This publication,Resistance to Plane-Stress Fracture(R-Curve Behavior)of A572 Structural Steel,is one of the papers presented at the Eighth National Symposium on Fracture Mechanics which was held at Brown University,Providence,R.I.,26-28 Aug.1974.A summary only appears in the proceedings of this symposium(Mechanics of Crack Growth,ASTM STP 590).The symposium was sponsored by Committee E-24 on Fracture Testing of Metals of the American Society for Testing and Materials.J.R.Rice and P.C.Paris,Brown University,presided as symposium co-chairmen.Related ASTM Publications Mechanics of Crack Growth,STP 590(1976),$45.25,04-590000-30 Fracture Analysis,STP 560(1974),$22.75,04-560000-30 Fracture Toughness and Slow-Stable Cracking,STP 559(1974),$25.25,04-559000-30 Fatigue and Fracture Toughness-Cryogenic Behavior,STP 556(1974),$20.25,04-556000-30 A Note of Appreciation to Reviewers This publication is made possible by the authors and,also,the unheralded efforts of the reviewers.This body of technical experts whose dedication,sacrifice of time and effort,and collective wisdom in reviewing the papers must be acknowledged.The quality level of ASTM publications is a direct function of their respected opinions.On behalf of ASTM we acknowledge with appreciation their contribution.ASTM Committee on Publications Editorial Staff Jane B.Wheeler,Managing Editor Helen M.Hoersch,Associate Editor Charlotte E.Wilson,Senior Assistant Editor Ellen J.McGlinchey,Assistant Editor Table of Contents ABSTRACT.INTRODUCTION.BASIC ELEMENTS OF R-CURVES.MATERIALS,EXPERIMENTAL WORK,AND ANALYSIS.Materials.Test Specimens and Conditions.Analytical Techniques.LEFM Technique.COS Technique.RESULTS AND DISCUSSION.i.R-Curve Results.IA.Summary of Basic Behavior.lB.Effects of Temperature for B=1.5-Inch Specimens.IC.Effects of Temperature for B=0.5-Inch Specimens.ID.Nature of Fracture-Instability Event.2.General Discussion.2A.Overall Scatter Observed in K c Results.2B Repeatability of K c Results for a Specific Test Method.2C.Load-Control vs Displacement-Control Test Methods.2D.Effect of Thickness(B=1.5 Inch vs B=0.5 Inch)for the Load-Control Test Method.2E.Local Variation in Fracture Toughness.2F.Comparison of K c and Kic Behaviors.2G.Reservations Concerning Present R-Curve Results.3.Significance of Present R-Curve Results.3A.Critical-Flaw-Size Calculations.3B.Application of Results to Structures.SUMMARY AND CONCLUSIONS.ACKNOWLEDGMENT.REFERENCES.GLOSSARY OF SYMBOLS.TABLES Page 1 2 5 6 6 7 i0 Ii ii 12 12 12 12 18 19 22 23 24 26 29 30 33 40 41 41 44 47 52 53 56 FIGURES STP591-EB/Feb.1976 RESISTANCE TO PLANE-STRESS FRACTURE(R-CURVE BEHAVIOR)OF A572 STRUCTURAL STEEL By S.R.Novak Abstract The R-curve behavior of A572 Grade 50 steel was established over the temperature range-40 to+72 F by using state-of-the-art procedures.Both linear-elastic-fracture-mechanics(LEFM)and crack-opening-stretch(COS)analytical techniques were used in assessing experimental results obtained under load-control and displacement-control testing conditions.This study represents a pioneer effort in that it is the first known attempt to evaluate the R-curve behavior of a low-strength structural steel in some depth.Results showed a steep K c transition behavior for 1.5-inch-thick(38 mm)plate,with minimum K c values of 57,155,and 318 ksi/inch(63,171,and 350 MNm-3/2)obtained at-40,+40 and+72 F(-40,+4.5,and+22 C),respectively.A similar behavior was ob-served for 0.5-inch-thick(12.7 mm)plate,with minimum K values of 150,273,and 380 ksi/inch(165,300,and 418 MNm-372)obtained at the corresponding test temperatures.The results are discussed in relation to the influence of material and testing method,as well as in relation to earlier Kic results obtained at cryogenic temperatures.The minimum K c values measured demonstrate extensive crack tolerance for A572 Grade 50 steel under all combinations of the test conditions studied.With one exception,these minimum behaviors can be translated into total critical flaw lengths that are at least 7 times the plate thickness(2acr 7B)for cracks embedded in large planar structures and subjected to tensile-stress levels equal to 3/4 the yield strength.The applicability of acr calculations obtained from R-curve measurements generally,and on the A572 Grade 50 steel specifically,is discussed in relation to typical structural m