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Introduction – Design against Failure Design-against-Failure Lecture 1 - Introduction Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Design process Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Definition of Failure Merriam Webster Dictionary • a) omission of occurrence or performance; specifically: a failing to perform a duty or expected action • b) a state of inability to perform a normal function • Mechanical Failure • “Any change in size, shape or mechanical properties of a structure, machine, or components that renders it incapable of satisfactory performing its intended function” – J.A. Collins, Failure of Materials in Mechanical Design, John Wiley&Sons, 1981 Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Type of failure • Type 1: Caused by negligence and • Type 2 – Caused by design change, use of professional misconduct during design new and untested materials that produce and/or construction and/or operation. in unexpected and undesirable results Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Type of failure: Type 1 • Type 1: Existing design guidelines and procedures are adequate to avoid failure but for a different reasons are nor followed. • Human error • Criminal behaviour • Poor manpower • Insufficient materials • Poor materials • Errors in stress analysis • Mistakes of operators • All of above Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Type of failure: type 2 • Type 2: is the most difficult type of failure to prevent. Introduction of design changes: unexpected results due to unpredictable or unknown factors of behavior. Examples: • Welding vs riveting Use of new materials: advantages but potential criticalities (unknown). Examples: • Use of polymers vs aluminum alloys • Titanium vs high strength steels Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure • Titanic (1912) – RMS Titanic was a British passenger ship hat sunk as a consequence of a collision with an iceberg, during her opening trip from Southampton (UK) to New York (USA), on april 14th, 1912. RMS Titanic was the largest ship of her time and considered “unsinkable”. In the disaster more than 1500 people lost their lives. • Causes. Several factors contributed to the disaster: • Insufficient number of lifeboats • Poor hull and rivet materials • Poor design of the watertight compartments Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure • Hindenburg disaster (1937) – LZ 129 Hindenburg was the largest passanger airship (273 m long) designed to route between Europe and Americas. During its 10th trip to US, it burst into flames while immediately after landing at Lakehurst Naval Air Station in Manchester Township, New Jersey. 36 lost their lives in the accident that was filmed live. • Cause: hydrogen fire probably started by electrostatic spaks. The disaster caused the end of an era. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure • Tacoma Narrows Bridge collapse (1940) – It was the first suspended bridge in the state of Washington and the 3rd longest single span bridge in US. Inaugurated in 1940, it collapsed the same year. The bridge showed unexpected vertical oscillatory motion under mild wind. On Nov. 7, 1940, the bridge under a wind blowing at 64 km/h collapsed. • Cause: • Change in the design to increase bending stiffness which caused the dynamic instability of the structure as a result of positive feedback between the body's deflection and the force exerted by the fluid flow (flutter) Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure • Cleveland East Ohio Gas Explosions (1944). On Oct. 20th, 1944, a tank of liquefied natural gas exploded in the town of Cleveland causing 130 deaths and damages for millions of dollars. • Cause: as a result of a leak, the released gas flowed in the city sewer mixing with air and vapors eventually ignited by a spark or a flame. • As a result of the accident, the norms and prescriptions for storages of inflammable gasses were redefined. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure • US Navy Liberty class(1943). Liberty class ships were the first to be build in a production line similarly to cars. Each section was produced separately and successively joined using welding instead of riveting. Over a global production of 2700 ships, 1500 were subjected to more or less severe brittle fractures. Three broke in two, in a case, while harboring. • Cause: investigation revealed the deadly combination of stress, crack like flaws and temperature on materials with limited crack resistance. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure • Hyatt Regency Hotel passerella Collapse (1981)- On July 7th, 1981, two suspended walkways at Hyatt Regency, Kansas City, collapsed on the mail hall killing 114 people. • Cause: Investigation revealed severe design flaw. The structure as it was designed, could barely sustain its dead load. • Consequences: Engineers that approved the design, were condemned for misconduct and negligence. Their license was withdrawn. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure • Space Shuttle Challenger avvenuta (1986) On Jan. 28, 1986 the Space Shuttle Challanged explosed after 73s after lift-off killing all 7 crewmembers. • Cause: Investigation showed that the disaster was caused by the failure of O-rings in the a joint of right SRB. The weakness of such critical component was known since many years ahead by NASA and contractor engineers but it instead of redesigning, it was treated as an acceptable risk. • Consequence: there years stop of NASA space program, and reorganization of quality assurance and safety office. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure • Chernobyl power plant disaster (1986) – Il On April 26 1986, following a series of stress tests, safety systems were intentionally turned off. A combination of inherent reactor design flaws and the reactor operators arranging the core in a manner contrary to the checklist for the test, eventually resulted in uncontrolled reaction conditions. The explosion of reactor IV released an enormous quantity of radiation in the atmosphere. The town of Pripyat, where 47.000 people lived, is a ghost town. The costs of such disaster were estimated in 235$ billion for 30 years on after the explosion. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Concorde Air France 4590 Crash (2000) - On July 25, 2000 Air France Concorde 4590 burst in flame and crashed immediately after take- off and at Paris Charles de Gaulle, killing 113 people. Initially, the age and distributed cracks in the structure was claimed as cause of the accident. Later investigation demonstrated that a series of unfortunate events caused the disaster: a tire debris on the runaway hit the lower surface of the wing, cutting the fuel line. The accident signed the end of the civil supersonic transport: 3 years later the Concorde was dismissed. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Space Shuttle Columbia disastro (2003) – On Feb. 1st, 2003, Space Shuttle Columbia disintegrated upon reentering the Earth’ atmosphere. During the launch, a piece of foam insulation broke off from the Space Shuttle external tank and struck the left wing of the orbiter. When Columbia re-entered the atmosphere of Earth, the damage allowed hot atmospheric gases to penetrate the heat shield and destroy the internal wing structure, which caused the spacecraft to become unstable and break apart. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Deepwater Horizon Disaster (2010). The Deepwater Horizon oil spill is an industrial disaster that began on 20 April 2010, in the Gulf of Mexico on the BP-operated Macondo Prospect. It is considered to be the largest marine oil spill in the history of the petroleum industry. The U.S. government estimated the total discharge at 780000 m3. After several failed efforts to contain the flow, the well was declared sealed on 19 Sep. 2010. The investigation found that managers misread pressure data and gave their approval for rig workers to replace drilling fluid in the well with seawater, which was not heavy enough to prevent gas that had been leaking into the well from firing up the pipe to the rig, causing the explosion. Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Approaches to Mechanical Design • FAIL-SAFE • SAFE-LIFE • DAMAGE TOLERANCE Mechanical Engineering Design - N.Bonora 2018 Introduction – Design against Failure Approaches to Mechanical Design • FAIL-SAFE This type of design philosophy considers the effects of failures and combinations of failures in defining a safe design. The principal idea is to see how a failure or failures could cause a negative effect in the safety of the design. The fail-safe design concept has two different meanings, one for structures and another one for the systems. Fail-Safe for a structure refers to the residual strength after the sustaining of damage, while the Fail-Safe concept for a system refers to the functional implications when a failure occurs and the possibilities that a failure occurs. The Fail-Safe for structures is governed by 14

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