Finite Elements in Analysis and Design 36 (2000) 99}133 Penetration simulation for uncontained engine debris impact on fuselage-like panels using LS-DYNA Norman F. Knight Jr! *, Navin Jaunky", Robin E. Lawson#, Damodar R. Ambur$ !Veridian MRJ Engineering, Yorktown, VA 23693-2619, USA "Eagle Aeronautics, Inc., Newport News, VA 23606, USA #Newport News Ship Building and Dry Dock Company, Newport News, VA 23607, USA $NASA Langley Research Center, Hampton, VA 23681-0001, USA Abstract Modeling and simulation requirements for uncontained engine debris impact on fuselage skins are proposed and assessed using the tied-nodes-with-failure modeling approach for penetration. A "nite element analysis is used to study the penetration of aluminum plates impacted by titanium impactors in order to simulate the e!ect of such uncontained engine debris impacts on aircraft fuselage-like skin panels. LS-DYNA is used in the simulations to model the impactor, test "xture frame and target barrier plate. The e!ects of mesh re"nement, contact modeling, and impactor initial velocity and orientation are studied using a con"g- uration for which limited test data are available for comparison. ( 2000 Elsevier Science B.V. All rights reserved. Keywords: Impact; Penetration; LS-DYNA; Finite elements 1. Introduction Prediction of the elasto-plastic, large-deformation, transient dynamic behavior involving impact of multiple deformable bodies continues to provide new insights into the response of complex structural systems subjected to extreme loading conditions or exposed to extreme environments (e.g., Refs. [1}3]). Much of the computational mechanics technology necessary for simulating this behavior evolved over decades of research sponsored in part by government laboratories which also have had access to large supercomputer facilities. The rapid development of a!ordable computer technology with high-speed processors, large memories, and large, fast secondary storage devices has contributed to the integration of these analysis tools within design and analysis groups * Corresponding author. E-mail address: [email protected] (N.F. Knight Jr.) 0168-874X/00/$ - see front matter ( 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 8 7 4 X ( 0 0 ) 00011-1 100 N.F. Knight Jr et al. / Finite Elements in Analysis and Design 36 (2000) 99}133 in industry. This technology transfer has provided methods and software that can be used to improve designs, reduce uncertainties, and increase product safety. One such application involves simulating the response of a fuselage skin when impacted by uncontained aircraft turbine-engine debris. Developing accurate "nite element models and analysis strategies for this event has the potential of signi"cantly improving the design, reliability, and safety of engines and primary aircraft structures, especially for commercial transport applications. Two potential hazards involving the turbine-engine debris are the subject of ongoing research e!orts. One event involves containing failed engine debris within the engine housing } contained failure. Examples of research in this area include Refs. [4}13]. The other event involves the potential impact of uncontained failed engine debris on other parts of the aircraft } uncontained failure. Examples of research in this area include Refs. [11}17]. The potential hazard resulting from an uncontained turbine engine failure has been a long-term concern of the Federal Aviation Administration (FAA), National Aeronautical and Space Adminis- tration (NASA), and the aircraft industry (e.g., see Refs. [4}17]). For the purpose of airplane evaluations, the FAA de"nes an uncontained failure of a turbine engine as any failure which results in the escape of rotor fragments from the engine or Auxiliary Power Unit (APU) that could result in a hazard (see Ref. [7]). A contained failure is one where no fragments are released through the engine structure; however, fragments may be ejected out the engine air inlet or exhaust. Rotor failures which are of concern are those where released fragments have su$cient energy to create a hazard to the airplane and its passengers. Failed rotating components can release high-energy fragments which are capable of penetrating the engine cowling and damaging the fuel tank, hydraulic lines, auxiliary power units, and other accessories [11]. The penetration capability of the material released is a!ected by its shape, orientation of impact, material properties, and kinetic energy. The high-energy fragments are dispersed circumferentially in all directions at very high velocities. When the fragments escape or penetrate the engine casing, the consequences can range from minor damage to catastrophic failures. These fragments, released during engine failure, a!ect the #ying performance of the aircraft in a number of direct or indirect ways, since they can impact and damage surrounding structures and equipment. Behaving as projectiles, these fragments have damaged surrounding runways, residences and vehicles [18,19]. Uncontained failure of engine rotating components in turbine engine aircraft is considered a serious safety hazard to occupants as well as to the aircraft itself. On August 22, 1985, a Boeing 737 operated by British Airtours, su!ered an uncontained failure in the left engine about 36 s into take-o! [20]. As the airplane approached an airspeed of 125 knots, a fragment punctured a wing fuel tank access panel. Fuel leaking from the wing ignited and burnt as a large plume of "re trailing directly behind the engine. As the aircraft turned o!, wind carried the "re onto and around the fuselage. Subsequently "re developed within the cabin. Despite the prompt attendance of the airport "re service, the aircraft was destroyed and "fty-"ve persons on-board lost their lives. The cause of the accident was attributed to an uncontained failure of the left engine, initiated by a failure of the No. 9 combustor can which had been the subject of a repair. A section of the combustor can, which was ejected forcibly from the engine, struck and fractured an underwing fuel tank access panel [20]. On June 8, 1995, as ValuJet Flight 597 began its take-o! roll, shrapnel from the right engine penetrated the fuselage and the right engine main fuel line, and a cabin "re erupted [21]. A #ight N.F. Knight Jr et al. / Finite Elements in Analysis and Design 36 (2000) 99}133 101 attendant received serious puncture wounds from shrapnel and thermal injuries; another #ight attendant and "ve passengers received minor injuries. An investigation revealed that an uncon- tained rotor failure in the right engine had occurred due to fatigue of its 7th stage high-compressor disc. According to National Transportation Safety Board (NTSB) "ndings, the maintenance and inspection personnel failed to perform a proper inspection of the disc, thus allowing the detectable crack to grow to a length at which the disc ruptured under normal operating conditions, propelling engine fragments into the fuselage; the fragments severed the right engine main fuel line, which resulted in a "re that rapidly engulfed the cabin area [21]. On July 6, 1996 in Pensacola, FL, Delta Airlines Flight 1288 experienced an uncontained failure of the left engine during the beginning take-o! roll about 1400 ft down the runway [23,24]. The 125 lb. hub fractured as the Pratt & Whitney engine approached maximum take-o! power, turning at 8000 rpm. Pieces of the hub and the attached fan section were #ung out at violent speed, tearing into the fuselage and hurling pieces to the right and left of the rolling aircraft (see Fig. 1). A mother and her 12-yr-old son died instantly as blades and fragments penetrated the cabin. The injuries involved two other children in the family. A total of seven passengers su!ered injury in the incident and during evacuation. A large fragment, which included a two-thirds chunk of the hub and a section of attached blades, gouged the runway and tumbled to a point 620 ft west of the runway. A second hub section, without blades attached, was found 2400 ft away, outside the airport perimeter. This site is east of the runway, on the opposite side of the aircraft from where the large piece was found. After investigation, the fan hub for the left engine was found fractured. The 1 in long crack, suspected to be of fatigue origin, was located inside a tierod hole through which one of twenty-four 0.5 in bolts attach the fan hub to the engine's low-pressure compressor [23]. According to the Aerospace Information Report 4003 [9], a total of 315 uncontained rotor failures occurred from 1976 to 1983 in commercial, general, and rotorcraft aviation. While the Fig. 1. Delta Flight 1288 uncontained engine failure (from Ref. [24]). 102 N.F. Knight Jr et al. / Finite Elements in Analysis and Design 36 (2000) 99}133 probability of failure is already low, turbine engine and APU manufacturers are making e!orts to reduce the probability of uncontained rotor failures; however, service experience shows that uncontained compressor and turbine rotor failures continue to occur. In 1997, statistics summariz- ing twenty-eight years of service experience for "xed-wing airplanes with over one billion engine- operating hours on commercial transports are presented [7]. A total of 676 uncontained engine failure events includes 93 events classi"ed in Category 3 and 15 events classi"ed in Category 4 damage to the airplane. Category 3 is de"ned as signi"cant airplane damage with the airplane capable of continuing #ight and making a safe landing. Category 4 damage is de"ned as severe airplane damage involving a crash landing, critical injuries, fatalities or hull loss. The events were caused by a wide variety of in#uences classi"ed as environmental (bird ingestion, cor- rosion/erosion), foreign object damage, manufacturing and material defects, mechanical, and human factors (i.e., maintenance and overhaul, inspection error, and operational procedures).