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FRACTURE MECHANICS. CRACK ?? FRACTURE ??? MECHANICS OF MATERIAL/STRENGTH OF MATERIAL ??. ASSUMPTION. HOMOGEN CONTINUE ISOTROPI. CASES. 1800 – 1870 : Accidents were caused by Fractures of wheel, axle, rails (Great Britain). 19 th March 1830 : Montrose Suspension Bridge.
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FRACTURE MECHANICS • CRACK ?? • FRACTURE ??? • MECHANICS OF MATERIAL/STRENGTH OF MATERIAL ??
ASSUMPTION • HOMOGEN • CONTINUE • ISOTROPI
CASES • 1800 – 1870 : Accidents were caused by Fractures of wheel, axle, rails (Great Britain). • 19th March 1830 : Montrose Suspension Bridge. Main chain gave way 700 persons killed. • 22nd January 1866 : A portion of roof of the Manchester railway station fell. 2 men death. Caused by failure of cast iron struts connected. • 13th December 1898 : The failure of a large gas tank in New York. • 3th January 1913 : A high pressure water burst at Boston flooded the district • February 1866 : Boiler explosions • Most of serious railway accidents • Spec pipa : API. 5 LX grade X52, electric • resistance welded, longitudinal weld pipa - Mechanical properties : σu, σy - Dimensi pipa : Ø 16” , t = 0,250” • Kondisi operasi : p = 600 psig (avg) • Sistem perlindungan • - Kondisi lingkungan POOR DESIGN
Fracture mechanics • LINEAR ELASTIC FRACTURE MECHANICS (LEFM) * BEBAN ELASTIS == FATIGUE • ELASTIC PLASTIC FRACTURE MECHANICS * BEBAN PLASTIS
STRESS CONCENTRATION FACTOR (Kt) • RADIUS OF FILLET • r/D • r/D<<< = Kt >>> • Notch stress (σnotch)>>> • σnotch = Kt x σunnotch/ σn Bagaimana kalau r ~ 0, D = constant r/D = 0/D ~ infinite = crack/retak Crack # notch/hole Kt = faktor pengendali konstruksi yang ada notch
SOURCES OF STRESS CONCENTRATED • IMPURITY,VACANCY,DISLOCATION,GRAIN BOUNDARY • ROUGHNESS OF SURFACE • WELD DEFECT • HOLE FOR RIVET, BOLT “DON’T CONSIDER TO AVOID FRACTURE”, BUT CONSIDER “TO CONTROL FRACTURE” IN DESIGN, MANUFACTURING, MAINTENANCE AND REPAIR.
What is CRACK???? • Notch yang r ~ 0 • Alat kontrolnya bukan lagi Kt • K1 , K2 atau K3 (factor intensitas tegangan/ stress intensity factor) • KI = MODUS I , tension • KII = modus II, sliding • KIII = modus III, tearing
Crack size Residual strength Design strength Expected highest service load Expected highest service load Normal sevice load Failure may occure failure Cycles/time Crack size, time
FRACTURE/PATAH • AWAL RETAK/CRACK INITIATION • CRACK PROPAGATION • FINAL FRACTURE
Others 23 % Static fracture 13% corrosion burst 3% SCC 5% TOTAL 242 SIMPLE FATIGUE 58% 77% FATIGUE CORROSIO FATIGUE ROLLING CONTACT FATIGUE 11 % Others 10 Thermal Fatigue 8 % Wire rope 8 Cast 15 90 % Stress concentration Welded part 77 242 Gear 18 Pulley,roll 28 Key, atc 56 Bolt 32
MODE OF FRACTURE Mixed Mode I & II I & III
FRACTURE MECHANICS PARAMETERS σy K = σvπ. a f (a/w) K = stress insity factor a = crack size f(a/w) = shape factor
Fracture toghness • Kc is fracture toughness value/ nilai ketangguhan retak • K ~ Kc === patah/fracture • K < Kc == crack propagation/menuju patah a ~ ac (critical size) patah Δ K = K max –K min K max = σ max V π. a f (a/w) K min = σ min V π. a f (a/w)
Unstable III da/dN • Crack initiation • Propagation • Final/static fracture II Stable crack Kc properties Fracture toughness value I Δ Kth Δ K K
Crack propagation (da/dN • PARIS LAW da/dN = C (Δ K)m Δ K = stress intensity range C , m = the material constant Δ K = K max – K min
P da/dN (log scale) ΔP1>ΔP2>ΔP3 a ΔP3 ΔP2 CRACK PROPAGATION ΔP1 b da/dN = C (ΔK)m t a da dN N(cycles) ΔK (log scale) ΔK = Δσ (πa)^1/2 f(a) P R=0 R = -1 P max + ΔP t(time) - P min
