FRACTURE MECHANICS n CRACK n FRACTURE n MECHANICS

FRACTURE MECHANICS n CRACK ? ? n FRACTURE ? ? ? n MECHANICS OF MATERIAL/STRENGTH OF MATERIAL ? ?

ASSUMPTION n HOMOGEN n CONTINUE n ISOTROPI

CASES Ø 1800 – 1870 : Accidents were caused by Fractures of wheel, axle, rails (Great Britain). Ø 19 th March 1830 : Montrose Suspension Bridge. Main chain gave way 700 persons killed. Ø 22 nd January 1866 : A portion of roof of the Manchester railway station fell. 2 men death. Caused by failure of cast iron struts connected. Ø 13 th December 1898 : The failure of a large gas tank in New York. Ø 3 th January 1913 : A high pressure water burst at Boston flooded the district Ø February 1866 : Boiler explosions Ø Most of serious railway accidents POOR DESIGN

Fracture mechanics n LINEAR ELASTIC FRACTURE MECHANICS (LEFM) * BEBAN ELASTIS == FATIGUE n ELASTIC PLASTIC FRACTURE MECHANICS * BEBAN PLASTIS

STRESS CONCENTRATION FACTOR (Kt) RADIUS OF FILLET n r/D<<< = Kt >>> n Notch stress (σnotch)>>> n 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 n

SOURCES OF STRESS CONCENTRATED n n 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 n Alat kontrolnya bukan lagi Kt n K 1 , K 2 atau K 3 (factor intensitas tegangan/ stress intensity factor) n K = MODUS I , tension n K = modus II, sliding n I II n KIII = modus III, tearing

Expected highest service load Crack size Residual strength Design strength Expected highest service load Normal sevice load Failure may occure failure Cycles/time Crack size, time

FRACTURE/PATAH AWAL RETAK/CRACK INITIATION n CRACK PROPAGATION n FINAL FRACTURE n

Others 23 % Static fracture 13% corrosion burst 3% SCC 5% CORROSIO FATIGUE ROLLING CONTACT FATIGUE TOTAL 242 SIMPLE FATIGUE 58% 77% FATIGUE 11 % Others 10 Thermal Fatigue 8% Cast 15 Gear Wire rope 8 18 Pulley, roll 90 % Welded part Stress concentratio 242 28 Bolt 32 Key, atc 56 77

MODE OF FRACTURE Mixed Mode I & III

FRACTURE MECHANICS PARAMETERS σy K = σ vπ. 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 n K ~ Kc === patah/fracture n 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) n

da/d. N III Unstable I. Crack initiation II II. Propagation III. Final/static fracture Stable crack I Δ Kth K Kc properties Fracture toughness value ΔK

Crack propagation (da/d. N n PARIS LAW da/d. N = C (Δ K)m Δ K = stress intensity range C , m = the material constant Δ K = K max – K min

CRACK PROPAGATION P da/d. N (log scale) ΔP 1>ΔP 2>ΔP 3 a ΔP 3 ΔP 2 ΔP 1 b da/d. N = C (ΔK)m t a da d. N N(cycles) ΔK = Δσ (πa)^1/2 f(a) P R=0 R = -1 P max + - ΔP P min t(time) ΔK (log scale)