Welding Mechanics and Fracture Assessment

Transcription

1 Welding Mechanics and Fracture Assessment Fumiyoshi Minami Joining and Welding Research Institute, Ibaraki,, JAPAN Abstract Recent progress in welding mechanics and fracture assessment procedures for weld structures in Japan is presented. The joining/welding mechanics and design emphasize the increasing need for a methodology to predict the structural performance and integrity from a stage of designing structures with the best use of materials. The presentation focuses on the computational methodologies for the simulation of welding/joining with emphasis on the reduction of welding residual stresses and distortion, and the fracture mechanics assessment of the structural integrity of weld components in terms of the ductile damage evaluation, fatigue design and analysis, and the standardization of the constraint-based assessment of unstable fracture. Computational Methodologies for Simulation of Welding and Joining - Simulation of Welding and Joining by Computational Approach [1], [2], [3] - High-Speed FEM for Welding Distortion and Stress Analysis [4] - Mechanics in Welding, Materials Processing and Fabrication [5] Fracture Mechanics Assessment of Structural Integrity of Weld Components - Damage Mechanics for Prediction of Ductile Fracture Performance of Welded Joints [6] - Fatigue Design and Analysis of Weld Structures [7] - International Standardization of Constraint-Based Assessment of Unstable Fracture [8], [9], [10] References [1] H. Serizawa, S. Nakamura, H. Tanigawa, H. Ogiwara and H. Murakawa: Numerical Study of Local PWHT Condition for EB Welded Joint between First and Side Walls in ITER-TBM, Journal of Nuclear Materials, Vol.442 (2013), pp.s535-s540. [2] H. Serizawa and F. Miyasaka: New Combined Method of MPS and FEM for Simulating Friction Stir Processing, Ceramic Engineering and Science Proceedings, Vol.36, Issue 2 (2015), pp [3] M. Shibahara, K. Ikushima, T. Harada, F. Kimura and T. Morimoto: Study on Solidification Cracking Under High-Speed Narrow Gap Welding with Tandem Torches, Proceedings of the 24th International Offshore and Polar Engineering Conference, (2015), pp [4] M. Mochizuki: Numerical Simulations of Micro-, Macro-, and Mega-Scale Structurization by Welding Processes, Mathematical Modelling of Weld Phenomena 10, TU Graz Publishing (Graz, 2013), pp [5] K.Ikushima and M.Shibahara: Large Scale Non-Linear Analysis of Residual Stresses in Multi-Pass Pipe Welds by Idealized Explicit FEM, Welding in the World, Vol.59, No.6 (2015), pp [6] M. Ohata, T. Fukahori and F. Minami: Damage Model for Predicting the Effect of Steel Properties on Ductile Crack Growth Resistance, International Journal of Damage Mechanics, Vol.19, (2010), pp [7] S. Tsutsumi, H. Momii and R. Fincato: Influence of tangential plasticity for elastoplastic behavior of a thin wall steel bridge pier under lateral bidirectional load paths, Journal of Structural Engineering, JSCE, Vol.62A (2016), pp [8] F. Minami, et al: Method of Constraint Loss Correction of CTOD Fracture Toughness for Fracture Assessment of Steel Components, Engineering Fracture Mechanics, Vol.73 (2006), pp [9] Y. Yamashiha and F. Minami: Constraint Loss Correction for Assessment of CTOD Fracture Toughness under Welding Residual Stress, Engineering Fracture Mechanics, Vol.77 (2010), pp , Vol.77 (2010), pp [10] F. Minami, M. Ohata and Y. Takashima: Revision of ISO for CTOD Toughness Correction for Constraint Loss, Materials Science and Forum, Thermec 2016, (2016)

2 Joining and Welding Research Institute!$+# *!&% & #!% &!%!% - &$'+* *!&% # ''(& ))& (& (!., Weld design for reducing residual stresses Prediction of welding distortion by inherent strain analysis Welded Part [MPa] x Weld Line z 10mm Simulation Result (Current Design) Original Deformation: x 40 y 16mm After Welded $($&,!!!!$, (Prospective Design)! (& %$* & %! #( Experimental Result Coupled method (MPS & FEM) for simulating FSW Finite Element Method Particle Method (MPS)! ' 1 &( #!%!)*&(*!&% % *( )) % #-)!) ))& (&! ( Residual stress analysis of multi-pass pipe-welds (108 passes, 3 million DOF) Development of large-scale FEM for welding mechanical analysis (IEFEM: Idealized Explicit FEM) Welding torch (MPa) Increase in DOF in welding mechanical analyses y z x 108 Analysis scale (DOF) 1,125,360 nodes 1,078,920 elements 3,376,074 dof Weld metal (ALLOY132) 1 ~ z = 0.0 A ~ Pass number z & % & x y Cladding (SUS308) A 75 &' & % & &! % & 104 ' % & & " % & % & & % & 103 & % & & & % & & % &!" % &! " % & * $ Base metal 2 (SFVQ1A) ##)(! " %! & 105 Base metal 1 (SUS316) Group number Year IEFEM enables large-scale nonlinear analysis with 10 million degrees of freedom (DOF) 102 times larger DOF 1/102 times shorter computational time Nonlinear analysis of welding distortion of ship-hull block (10 million DOF) Welding distortion and residual stresses in structural members can be predicted by IEFEM. 2

3 Welding & Joining Academic fusion of welding mechanics, arc physics, and materials science Materials Processing Estimation of mechanical properties of welds by process mechanics Fabrication & Assembly Experiment Simulation Microscopic stress and strain evaluation in grain scale Evaluation of stress/strain of machined surface High-precision prediction of distortion in assembly process of large-scale structures 3 Bead profilethermal cycle Material properties, Residual stress Determination of ductile damage controlling parameters Notched bend specimen Round notched tension specimen Weld component model Weld component model Geometrical discontinuity Material/Mechanical heterogeneity Pipe fracture performance Crack in HAZ Simulated crack growth Girth weld Ductile fracture Notch ductility R=1, 2, 5 (mm) Stress triaxiality dependent ductility HAZ BM WM Proposal of mechanical properties for improvement of ductile performance 2 Simulation Prediction of fracture performance Advanced damage model Φ = Σ + a 1 D * Σ exp a m 2 1 = 0 σ σ M (MN m) Bend Bending test test Experiment Prediction Prediction of failure of failure in FEA by FEA θ e (deg.) Ductile crack initiation/growth resistance of component is controlled by two material properties; notch ductility and stress triaxiality dependent ductility. Advanced damage model is developed, where the damage parameters are inferred from the notch ductility and stress triaxiality dependent ductility. Advanced damage mechanics enables prediction of pipe fracture performance with ductile crack growth. 4

4 Joining and Welding Research Institute %* (% *!&% # ) ( %* ( &( *! + )! % & # *(+ *+( ) FDWS aims at developing an advanced methodology to prevent fracture and to ensure the safe operation of structures from a stage of designing structures. The key concept is the visualization of crack performance, leading to fatigue free structures, with the standardization of fatigue assessment procedure. Current Research Subjects 1. Critical review of current studies on fatigue design 2. Link between fatigue initiation at structural discontinuity and fracture mechanics approach 3. Constraint-based assessment of fatigue 4. Development of fatigue tests leading to fracture performance design for weld structures 5. International standardization of performance oriented design for fatigue assessment (since April ) 5 Joining and Welding Research Institute Thin Wall Pier % #-)!) & # )*& # )*! ( &($ *!&% & #! () +% ( &% (&'&(*!&% # - #! &!% ))& (& )+*)+$! ( ' (' Rectangular Cross-Section Pier $#) #( $#! $#! "$! &$%$' "$! "$! $%$' "$ &! +% & " #(! ( 6

5 Constraint Loss in Tension Components Plastic constraint Plastic zone confined by neutral axis ahead of crack Specimen geometry / Loading mode Tension Toughness K c, δ c, J c ( ) >> K c, δ c, J c ( ) components specimen 7 Standardization ISO Japanese IST Project Project leader: F. Minami ( ) 8

6 Equivalent CTOD ratio, β ISO Equivalent CTOD ratio β = δ / δ WP (0 < β < 1) at the same Weibull stress level Proposed originally by Minami et al. at 18th Int. Conf. OMAE, St. John's, Canada (1999) Fracture toughness specimen Compact 3PB a 0 W (a 0 /W = 0.5) Weibull stress σ W a 0 W δ δ WP Structural component CTOD Fracture toughness specimen δ cr δ R = β δ WP R Structural component δ WP,cr = δ cr / β δ WP R Weibull stress, 1 σ W = V 0 σ eff m dv f 1/ m 9 Fracture Assessment on FAD with β ISO ESCP σ t = 25 SM490B (JIS G 3106) (R Y = σ Y / σ T = 0.7) W B = t a0 = B H a 0 / W = 0.5 δ cr = 0.022mm (0.2MOTE : 24 tests) Fracture assessment δ WP,cr = δ cr / β W = 195 L/2 = 370 c=20 c=20 H a=6 a=6 L/2 = 370 W=100 σ (Unit : mm) Fracture ratio, δ r SM490B, YR=0.7 E No-correction (β=1) J Level I (β=0.5) B Level II & III (β=0.17) ESCP (2c=40mm, a=6mm) BS7910 Level 2A-FAC at -100 C L r max = 1.11 Level 2B-FAC Load ratio, L r = σ ref / σ Y 10

7 Equivalent CTOD Ratios, β and β r β = δ / δ WP : for structural component without σ r β r = δ / δ WP, active : for structural component with σ r at the same Weibull stress level Fracture toughness specimen 3PB Compact a 0 W (a 0 /W = 0.5) a 0 W δ δ WP Weibull stress σ W Structural component without σ r Structural component with σ r δ WP, active Active CTOD, δ active δ WP, active : WP CTOD by applied stress (CTOD by σ r is not included) At contained yielding: β < β r, Atgeneral yielding: β β r 11 Fracture Assessment on FAD Fracture ratio, δ r HT780 No Correction (β = 1) β r BS7910: 2005 L r, max Level 2A-FAC = HT780 wide plate joints m= Load ratio, L r = σ ref / σ Y β 2a=42 HT780 BS7910 (β=1) Correction by β r Correction by β 12

8 Revised Points ISO Rev. New chapter: Conditions for use Upper limit of R Y (= σ Y /σ T ) Expanded to 0.98 Weibull parameter, m, at Level II assessment Annex A Main body Equivalent CTOD ratio, β, for surface cracked plates: CSCP, ESCP β = f (R Y, a, m) β = f (R Y, a, t, m): improved accuracy Annex D: Fracture assessment on FAD BS7910: 2005 BS7910: 2013 NOTE The scope and main frame are not changed. 13 ISO Revised ISO Rev. ISO / FDIS Closing date for voting: July 18, 2016 FDIS voting results Votes by P-members Approval: 13 Disapproval: 1 Abstention: 7 13/14 ISO Rev. was approved. 14