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Fatigue Problems in Civil and Aerospace Structures

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## Fatigue Problems in Civil and Aerospace Structures

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**Fatigue Problems in Civil and Aerospace Structures**Dr. Ribelito F. Torregosa, CIT-U BSCE ‘91 Research Scientist - Aerospace Division Defence Science and Technology Group Cebu Institute of Technology – University Alumni Association (CIT-UAA) Lecture Series Program**UNCLASSIFIED**About me Japan (Gifu University) • Ph. D. (Earthquake Eng’g.) - 2002 Thailand (Asian Instiute of Technology) • Master of Eng’g (Structural) - 1998 Philippines ( CIT-91) • BS Civil Eng’g. Australia • Defence Science and Technology Group (Research Scientist)**UNCLASSIFIED**What is Fatigue Failure? Fatigue failure - is a phenomenon where structures fail when subjected to a cyclic load Which loading will cause fatigue failure? P P time P time**UNCLASSIFIED**Dynamic loads - cause of fatigue failures Civil engineering structures Aircraft structures Air pressure - variable Ground shaking due to earthquakes**UNCLASSIFIED**Deficiency in Earthquake Static load design of structures Load case 2 Load case 1 Does not consider accumulated damage**UNCLASSIFIED**Crack propagation due to fatigue loads Tension Compression Crack size increase with each load cycle**UNCLASSIFIED**Fatigue Failures in Civil Engineering EARTHQUAKE**UNCLASSIFIED**Earthquake occurrences worldwide Number of occurrences every year = 10,000+ Philippines Australia Source: Wikipedia**Ring of Fire**- high volcanic and seismic activity (earthquakes). Most of the active volcanoes on Earth are located on this circumference. Alaska (USA) California (USA) Japan Philippines Mexico Peru Indonesia Chile New Zealand**UNCLASSIFIED**Locating the epicenter of an earthquake Seismograph station Earthquake epicentre Earth’s surface P-wave S-wave Earthquake hypocentre P-wave (pressure) – travels faster, low amplitude S-wave (shear) – travels slower, high amplitude**UNCLASSIFIED**Locating the epicenter of an earthquake Seismograph station Earthquake epicentre Earth’s surface S-wave Earthquake hypocentre P-wave P-wave (pressure) – travels faster, low amplitude S-wave (shear) – travels slower, high amplitude**UNCLASSIFIED**Locating the epicenter of an earthquake S wave arrival time P wave arrival time Seismogram • Time of arrival of P and S waves known • Distance of earthquake starting point (i.e., epicenter) from seismograph station known**UNCLASSIFIED**Distance travelled given Time of arrival and Speed Given: one car from unknown starting point Distance (D) Speed (V1) =100 kph Arrival time (t1)=10:00am ?? ?? 100 • Information not enough to solve Distance (D)**UNCLASSIFIED**Distance travelled given Time of arrival and Speed Given: two cars from unknown starting point Distance (D) Arrival times =10:00am Speed (V1) =100 kph Speed (V2) =50 kph =12:00am Distance travelled by car 1 = Distrancetravelled by car 2 +2 hours) 2 hours**UNCLASSIFIED**Two main factors causing fatigue failure to structures Ground acceleration Ground Motion duration Low acceleration Long duration High acceleration Short duration Earthquake source near far**UNCLASSIFIED**Earthquake ground motion duration P-wave S-wave duration duration Low acceleration Long duration High acceleration Short duration Earthquake source near far**UNCLASSIFIED**Locating the epicenter of an earthquake Legend : Earthquake epicenter somewhere along the circle Seismograph Station D1**UNCLASSIFIED**Locating the epicenter of an earthquake Legend : Seismograph Station Epicenter here D2 D3 D1**Minimizing fatigue failures in civil engineering structures**Seismic Hazard Mapping**Minimizing fatigue failures in civil engineering structures**Tuned mass damper Base isolation**UNCLASSIFIED**Fatigue Problems in Aircraft Structures**UNCLASSIFIED**Cost of ownership of military aircraft Cost to purchase: $330 million Cost to fly per hour: $206,337 Manufacturer: Boeing Model: VC – 25 e.g., “ Air Force One”**UNCLASSIFIED**Cost of ownership of military aircraft Cost to purchase: $210 million Cost to fly per hour: $173,253 Manufacturer: Lockheed Martin Model: AC – 130H Mission : “Special Operation”