ULTRA HIGH TEMPERATURE MECHANICAL TESTING

By STEVEN MARTINEZ

CONTENTS ANALYSIS OF A POWER PLANT ROTOR MADE OF TEMPERED MARTENSITIC STEEL BASED ON A COMPOSITE MODEL OF INELASTIC DEFORMATION COMPUTATIONAL ASSESSMENT OF THE MICROSTRUCTURE-DEPENDENT THERMOMECHANICAL BEHAVIOUR OF ALSI12CUNIMG-T7—METHODS AND MICROSTRUCTURE-BASED FINITE ELEMENT ANALYSES PROBLEMS OF THICK FUNCTIONALLY GRADED MATERIAL STRUCTURES UNDER THERMOMECHANICAL LOADINGS STRUCTURAL ANALYSIS OF GAS TURBINE BLADES MADE OF MO-SI-B UNDER STATIONARY THERMO-MECHANICAL LOADS EFFECTS OF SECOND PHASES IN MO-ZR ALLOYS-A STUDY ON PHASE EVOLUTION AND MECHANICAL PROPERTIES INVESTIGATING THE EFFECT OF CREEP PROPERTIES MISMATCH IN VERY THIN PIPES WITHIN HIGH-TEMPERATURE FACILITIES COHESIVE ZONE MODELS—THEORY, NUMERICS AND USAGE IN HIGH-TEMPERATURE APPLICATIONS TO DESCRIBE CRACKING AND DELAMINATION STABILITY OF PARAMETER IDENTI?CATION USING EXPERIMENTS WITH A HETEROGENEOUS STRESS STATE SHORT TERM TRANSVERSALLY ISOTROPIC CREEP OF PLATES UNDER STATIC AND PERIODIC LOADING ANALYSIS OF A POWER PLANT ROTOR MADE OF TEMPERED MARTENSITIC STEEL BASED ON A COMPOSITE MODEL OF INELASTIC DEFORMATION ABSTRACT POWER PLANT COMPONENTS ARE SUBJECTED TO HIGH TEMPERATURES UP TO 903 K, WHICH INDUCE CREEP DEFORMATIONS FURTHERMORE, POWER PLANTS ARE FREQUENTLY STARTED AND SHUT-DOWN, THUS RESULTING IN CYCLIC LOADS ON THE COMPONENTS SINCE THEY PRO- VIDE ADEQUATE MECHANICAL AND THERMAL PROPERTIES, TEMPERED MARTENSITIC STEELS ARE IDEAL CANDIDATES TO WITHSTAND THESE CONDITIONS THE CONTRIBUTION AT HAND PRESENTS A PHASE MIXTURE MODEL FOR SIMULATING THE MECHANICAL BEHAVIOR OF TEMPERED MARTENSITIC STEELS AT HIGH TEMPERATURES TO PROVIDE A UNI?ED DESCRIPTION OF THE RATE-DEPENDENT DEFORMATION INCLUDING HARDENING AND SOFTENING, THE MODEL MAKES USE OF AN ISO-STRAIN APPROACH INCLUDING A HARD AND A SOFT CONSTITUENT THE MODEL IS IMPLEMENTED INTO THE ?NITE ELEMENT METHOD, USING THE IMPLICIT EULER METHOD FOR TIME INTEGRATION OF THE EVOLUTION EQUATIONS IN ADDITION, THE CONSISTENT TANGENT OPERATOR IS DERIVED AS A ?NAL STEP, THE BEHAVIOR OF AN IDEALIZED STEAM TURBINE ROTOR DURING A COLD START AND A SUBSE- QUENT HOT START IS SIMULATED BY MEANS OF A THERMO-MECHANICAL ?NITE ELEMENT ANALYSIS FIRST, THE HEAT TRANSFER ANALYSIS IS CONDUCTED, WHILE PRESCRIBING THE INSTATIONARY STEAM TEMPERATURE AND THE HEAT TRANSFER COEF?CIENTS THE RESULTING TEMPERATURE ?ELDS SERVE AS INPUT FOR THE SUBSEQUENT STRUCTURAL ANALYSIS, WHICH YIELDS THE STRESS AND STRAIN ?ELDS IN THE ROTOR INTRODUCTION IN SERVICE, POWER PLANT COMPONENTS ARE SUBJECTED TO CHALLENGING CONDITIONS, SUCH AS HIGH TEMPERATURES AND INTERMITTENT LOADS STEAM TEMPERATURES SHOULD BE AS HIGH AS POSSIBLE TO INCREASE THE EF?CIENCY OF POWER PLANTS, SUCH THAT TEMPERATURES UP TO 903 K ARECOMMON[1–4] INADDITION,FREQUENTSTART-UPSANDSHUT-DOWNSINDUCECYCLICLOADS, WHICH IS DUE TO THE INCREASING POPULARITY OF RENEWABLE ENERGY SOURCES SUCH AS SOLAR AND WIND ENERGIES SINCE THIS TYPE OF ENERGY PRODUCTION STRONGLY DEPENDS ON THE AMBIENT CONDITIONS, CONVENTIONAL POWER PLANTS ARE STARTED AND SHUT-DOWN IN ORDER TO COMPENSATE GAPS OR SURPLUSES IN ENERGY PRODUCTION THESE CYCLIC LOADS FEATURE LONG HOLDING TIMES (TYPICALLY SEVERAL HOURS UP TO ONE MONTH) [3, 5–8], AS DEPICTED SCHEMATICALLY IN FIG 1 TEMPERED MARTENSITIC STEELS WITH HIGH CHROMIUM CONTENT (9–12%) ARE COMMONLY USED MATERIALS FOR POWER PLANT COMPONENTS [9–13], CF FIG 1 DUE TO THEIR OUTSTANDING THERMO-MECHANICAL PROPERTIES, SUCH AS HIGH TENSILE AND CREEP STRENGTH, A LOW COEF?- CIENT OF THERMAL EXPANSION, AND HIGH CORROSION RESISTANCE [5, 11, 13–17], TEMPERED MARTENSITIC STEELS ARE IDEAL CANDIDATES FOR OPERATIONS IN POWER PLANTS THE CONTRIBU- TION AT HAND PRESENTS A CONSTITUTIVE MODEL, WHICH IS CALIBRATED WITH MATERIAL TESTS ON THE ALLOY X20CRMOV12-1, A TYPICAL REPRESENTATIVE OF TEMPERED MARTENSITIC STEELS FROM THE 1950S, THIS STEEL HAS BEEN UTILIZED FOR FORGED COMPONENTS OF TURBINE SHAFTS FOR HIGH-PRESSURE APPLICATIONS AS WELL AS TUBES AND PRESSURE VESSELS [18] TURBINE WHEEL FIG 1 POWER PLANT COMPONENTS AND A TYPICAL TEMPERATURE PRO?LE WITH DAY–NIGHT CYCLES, CF [19] PICTURE OF TURBINE WHEEL ACCORDING TO [20] ULTRA HIGH TEMPERATURE MECHANICAL TESTING ?? = ˆ?/?T ?? = ˆ?/?T ?? = ?ˆ?/?T ?T 3?T 4?T ?ˆ? +ˆ? T [S] ? [?] FATIGUE TESTS (INPUT) F =5 HZ FATIGUE TESTS (OUTPUT) ?196 MPA ?185 MPA ?175 MPA ?230 MPA ?150 MPA COMPRESSION CREEP TESTS HT TENSILE TESTS FIG 2 MATERIAL TESTS ON X20CRMOV12-1 AT 873 K STRAIN ? VERSUS TIME T FOR ONE CYCLE DURING FATIGUE TESTS WITH PRESCRIBED STRAIN AMPLITUDES ˆ? (TOP LEFT), STRESS AMPLITUDE ˆ? VERSUS NUMBER OF CYCLES NC AS RESULT OF FATIGUE TESTS [8] (TOP RIGHT), ABSOLUTE INELASTIC STRAIN RATE |??IN| VERSUS ABSOLUTE INELASTIC STRAIN |?IN| FOR CREEP TESTS UNDER CONSTANT COMPRESSIVE STRESS ? [9] (BOTTOM LEFT), STRESS ? VERSUS STRAIN ? FOR HIGH TEMPERATURE (HT) TENSILE TESTS AT CONSTANT STRAIN RATES ?? (BOTTOM RIGHT), CF [19, 21] NEVERTHELESS, TEMPERED MARTENSITIC STEELS SUFFER FROM SOFTENING UNDER CREEP AND FATIGUE LOADS [3, 6–10, 22–25] UNDER CREEP CONDITIONS, THE SOFTENING EFFECT RESULTS IN AN INCREASE OF THE STRAIN RATE WITH TIME AND DEFORMATION [26], AS IT CAN BE OBSERVED IN THE BOTTOM LEFT DIAGRAM OF FIG 2, WHERE THE RESULTS OF CREEP TESTS UNDER CONSTANT COMPRESSIVE STRESS LEVELS ARE PRESENTED IT HAS BEEN FOUND THAT SOFTENING IS BASED ON THE COARSENING OF MICROSTRUCTURAL ELEMENTS, SUCH AS SUBGRAINS AND CARBIDES [9, 22–24] THIS SOFTENING EFFECT OCCURS ALSO UNDER CYCLIC LOADS [8], AS IT IS SHOWN IN THE TOP DIAGRAMS OF FIG 2 HERE, THE INPUT AND THE RESULTS OF STRAIN-CONTROLLED FATIGUE TESTS AT 873 K ARE PRESENTED NOTE THAT THE TOTAL STRAIN ? IS PRESCRIBED AS A TRIANGULAR FUNCTION OF TIME WITH A FREQUENCY OF F = 5 HZ THE TOP RIGHT DIAGRAM DEPICTS THE STRESS AMPLITUDE ˆ? WITH RESPECT TO THE NUMBER OF CYCLES NC FOR DIFFERENT PRESCRIBED AMPLITUDES OF TOTAL STRAIN ˆ? IT BECOMES OBVIOUS THAT THE STRESS AMPLITUDE REDUCES OVER TIME, WHICH IS DUE TO CYCLIC SOFTENING [8] SEVERAL PAPERS CON?RM THE CYCLIC SOFTENING EFFECT FOR TEMPERED MARTENSITIC STEELS, AND THIS PHENOMENON IS ATTRIBUTED TO THE COARSENING OF SUBGRAINS [3, 6, 7, 10, 25, 27] IN ADDITION, SOFTENING CAN ALSO BE OBSERVED DURING HIGH TEMPERATURE (HT) TENSILE TESTS [14–16, 28] AT ELEVATED TEMPERATURES AND LOW STRAIN RATES, THE STRESS DECREASES STEADILY AS THE STRAIN INCREASES, AS IT IS ALSO SHOWN IN THE BOTTOM RIGHT DIAGRAM OF FIG 2, WHERE STRESS-STRAIN CURVES ULTRA HIGH TEMPERATURE MECHANICAL TESTING