Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “failure simulation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Failure Mode Analysis of V-Shaped Pyrotechnically Actuated Valves

Current V-shaped stainless steel pyrovalve initiators have rectified many of the deficiencies of the heritage Y-shaped aluminum design. However, a credible failure mode still exists for dual simultaneous initiator (NSI) firings in which low temperatures were detected at the booster cap and less consistent ignition was observed than when a single initiator was fired. In order to asses this issue, a numerical framework has been developed for predicting the flow through pyrotechnically actuated valves. This framework includes a fully coupled solution of the gas-phase equation with a non-equilibrium dispersed phase for solid particles as well as the capability to model conjugate gradient heat transfer to the booster cap. Through a hierarchy of increasingly complex simulations, a hypothesis for the failure mode of the nearly simultaneous dual NSI firings has been proven. The simulations indicate that the failure mode for simultaneous dual NSI firings may be caused by flow interactions between the flame channels. The shock waves from each initiator interact in the booster cavity resulting in a high pressure that prevents the gas and particulate velocity from rising in the booster cap region. This impedes the bulk of the particulate phase from impacting the booster cap and reduces the heat transfer to the booster cap since the particles do not impact it. Heat transfer calculations to the solid metal indicate that gas-phase convective heat transfer may not be adequate by itself and that energy transfer from the particulate phase may be crucial for the booster cap burn through.

Sachdev, Jai S.↗
NASA NTRS1994

Probabilistic inspection strategies for minimizing service failures

The INSIM computer program is described which simulates the 'limited fatigue life' environment in which aircraft structures generally operate. The use of INSIM to develop inspection strategies which aim to minimize service failures is demonstrated. Damage-tolerance methodology, inspection thresholds and customized inspections are simulated using the probability of failure as the driving parameter.

Brot, Abraham↗
NASA NTRS2010

Rocket Cratering in Simulated Lunar and Martian Environments

With NASA's planned return to the moon and possibly with lunar outposts being formed, repeated landings at the same site will be necessary. Understanding rocket plume interaction with lunar and Martian surfaces is of paramount importance in order to safely land and protect hardware surrounding the landing site. This work will report on results of three small experiments intended to explore plume impingement onto lunar and Martian surfaces: Handheld Observation of Scour Holes (HOOSH), Handheld Angle of Repose Measurements of Lunar Simulants (HARMLuS), and Mars Architecture Team study (MATS). The first two experiments were performed during two sorties of reduced gravity flights. HOOSH was designed to investigate crater formation as a function of gravitational level (lunar and Martian gravity). HARMLuS was designed to measure the Angle of Failure (related to the angle of repose) at lunar and Martian gravity. Both experiments have complex findings indicative of the hysteretic behavior of granular materials, especially resulting from reduced gravity. The MATS experiment was designed to investigate the effects of regolith compaction on the granular mechanics of crater formation . In general, the granular mechanics is a much stronger function of compaction than gravitation acceleration. Crater formation is greatly enhanced at reduced gravity (resulting in much larger craters). The angle of failure of the lunar simulants increases with decreasing gravitational acceleration, and occasionally becomes infinite for some compactions at lunar gravity. The angle of failure also increases with increasing compaction. While compaction does play a role in the time development of crater formation, the asymptotic behavior is largely unaffected.

Immer, Christopher↗
NASA NTRS2009

[A Handling Qualities Metric for Damaged Aircraft]

In recent flight tests of F-15 Intelligent Flight Control System (IFCS), software simulated aircraft control surface failures were inserted to evaluate the IFCS adaptive systems. The failure commanded the left stabilator to a fixed position. The adaptive system uses a neural network that is designed to change control law gains, in the event of damage (real or simulated), that allows the aircraft to fly as it had before the damage. The performance of the adaptive system was assessed in terms of its ability to re-establish good onboard model tracking and its ability to decouple roll and pitch response.

Cogan, Bruce↗
NASA NTRS2017

Implementation of a Tabulated Failure Model Into a Generalized Composite Material Model Suitable for Use in Impact Problems

The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites under impact conditions is becoming critical as these materials are gaining increased use in the aerospace and automotive communities. The aerospace community has identified several key capabilities which are currently lacking in the available material models in commercial transient dynamic finite element codes. To attempt to improve the predictive capability of composite impact simulations, a next generation material model is being developed for incorporation within the commercial transient dynamic finite element code LS-DYNA. The material model, which incorporates plasticity, damage and failure, utilizes experimentally based tabulated input to define the evolution of plasticity and damage and the initiation of failure as opposed to specifying discrete input parameters such as modulus and strength. The plasticity portion of the orthotropic, three-dimensional, macroscopic composite constitutive model is based on an extension of the Tsai-Wu composite failure model into a generalized yield function with a non-associative flow rule. For the damage model, a strain equivalent formulation is used to allow for the uncoupling of the deformation and damage analyses. For the failure model, a tabulated approach is utilized in which a stress or strain based invariant is defined as a function of the location of the current stress state in stress space to define the initiation of failure. Failure surfaces can be defined with any arbitrary shape, unlike traditional failure models where the mathematical functions used to define the failure surface impose a specific shape on the failure surface. In the current paper, the complete development of the failure model is described and the generation of a tabulated failure surface for a representative composite material is discussed.

polymer matrix composites↗
NASA NTRS2018

Simulation Tool for Damage in Composite Laminates

A numerical simulation tool for progressive failure in laminates utilizes a low fidelity approach. The numerical model includes an enriched element that is initially in a low fidelity form. The enriched elements may increase fidelity by splitting locally to simulate an ongoing damage process such as delamination.

McElroy, Mark W.↗
NASA NTRS2002

Non-Coalescence in Microgravity: Science and Technology

In this project we examine non-coalescence and non-wetting phenomena driven by either thermocapillary convection or forced motion of one surface relative to the other. In both cases, the non-coalescence or non-wetting is enabled by the existence of a lubricating layer of gas that exists to keep the two surfaces in question from coming into contact with one another. Recent progress has been made on several fronts: 1) measurement of the vibrational modes of pinned droplets; 2) development of an apparatus for the measurement of the frictional forces associated with a non-wetting droplet sliding over a solid surface; 3) measurements of the failure modes for non-wetting droplets and the influence of static electric charge on failure-, and 4) numerical simulation of a two-dimensional non-wetting droplet revealing a possible explanation for why the phenomenon has not been able to be observed using water as the droplet liquid. Issue 1) above is of relevance to the use of non-wetting droplets as positioning mechanisms and vibration dampers in a microgravity environment; issue 2) relates to the use of non-wetting droplets as nearly 'frictionless' bearings in low-load applications. Understanding of the failure modes identified in 3) is of importance to any potential application and the numerical simulations conducted under 4) allow us to obtain information about these systems that is currently not available through experimentation Each of these topics will be discussed briefly during the presentation.

Neitzel, G. Paul↗
NASA NTRS1990

Probabilistic high cycle fatigue failure analysis with application to liquid propellant rocket engines

A probabilistic high cycle fatigue (HCF) failure analysis of a welded duct in a rocket engine of the Space Shuttle main engine class is described. A state-of-the-art HCF failure prediction method was used in a Monte Carlo simulation to generate a distribution of failure lives. A stochastic stress/life model is used for material characterization, and a composite stress history is generated for accurately deriving the stress cycles for the fatigue-damage calculations. The HCF failure model expresses fatigue life as a function of stochastic parameters including environment, loads, material properties, geometry, and model specification errors. A series of HCF failure life analyses were performed to study the impact of a fixed parameter and to assess the importance of each stochastic input parameter through marginal analyses.

Sutharshana, S.↗
NASA NTRS1990

Probabilistic low cycle fatigue failure analysis with application to liquid propellant rocket engines

A probabilistic Low Cycle Fatigue (LCF) failure analysis of a candidate turbine disk for use in a turbopump of a rocket engine of the Space Shuttle Main Engine class is described. A state-of-the-art LCF failure prediction method was used in a Monte Carlo simulation to generate a distribution of failure lives. A stochastic Stress/Life (S/N) model was used for materials characterization. The LCF failure model expresses fatigue life as a function of stochastic parameters including environmental parameters, loads, material properties, structural parameters, and model specification errors. The rationale for the particular characterization of each stochastic input parameter is described. The results and interpretation of the failure analysis are given.

Newlin, L.↗
NASA NTRS2000

Simulation of X-38 Landing Scenarios With Landing Gear Failures

Abnormal landing scenarios of the X-38 prototype Crew Rescue Vehicle (CRV) were modeled for three different cases involving non-deployment of landing gear with an explicit dynamic nonlinear finite element code, MSC/DYTRAN. The goal of this research was to develop models to predict the probability of crew injuries. The initial velocity conditions for the X-38 with chute deployed were 10 ft/s vertical and 57 ft/s longitudinal velocity. An MSC/NASTRAN structural model was supplied by JSC and was converted to a dynamic MSC/DYTRAN model. The MSC/NASTRAN model did not include seats or floor structure; thus, the acceleration of a lumped-mass attached to the bulkhead near each assumed occupant location was used to determine injury risk for each occupant. The worst case for injury was nondeployment of all gears. The mildest case was nondeployment of one main gear. Although a probability for minor injury was predicted for all cases, it is expected that the addition of energy-absorbing floor structure and seats would greatly diminish the probability of injury.

Fasanella, Edwin L.↗
NASA NTRS2018

Differential Adaptive Stress Testing of Airborne Collision Avoidance Systems

The next-generation Airborne Collision Avoidance System (ACAS X) is currently being developed and tested to replace the Traffic Alert and Collision Avoidance System (TCAS) as the next international standard for collision avoidance. To validate the safety of the system, stress testing in simulation is one of several approaches for analyzing near mid-air collisions (NMACs). Understanding how NMACs can occur is important for characterizing risk and informingdevelopment of the system. Recently, adaptive stress testing (AST) has been proposed as a way to find the most likely path to a failure event. The simulation-based approach accelerates search by formulating stress testing as a sequential decision process then optimizing it using reinforcement learning. The approach has been successfully applied to stress test a prototype of ACAS Xin various simulated aircraft encounters. In some applications, we are not as interestedin the system's absolute performance as its performance relative to another system. Such situations arise, for example, during regression testing or when deciding whether a new system should replace an existing system. In our collision avoidance application, we are interested in finding cases where ACAS X fails but TCAS succeeds in resolving a conflict. Existing approaches do not provide an efficient means to perform this type of analysis. This paper extends the AST approach to differential analysis by searching two simulators simultaneously and maximizing the difference between their outcomes. We call this approach differential adaptive stress testing (DAST). We apply DAST to compare a prototype of ACAS X against TCAS and show examples of encounters found by the algorithm.

Lee, Ritchie↗
NASA NTRS2017

Incorporation of Failure Into an Orthotropic Three-Dimensional Model with Tabulated Input Suitable for Use in Composite Impact Problems

The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites under impact conditions is becoming critical as these materials are gaining increased use in the aerospace and automotive communities. The aerospace community has identified several key capabilities which are currently lacking in the available material models in commercial transient dynamic finite element codes. To attempt to improve the predictive capability of composite impact simulations, a next generation material model is being developed for incorporation within the commercial transient dynamic finite element code LS-DYNA. The material model, which incorporates plasticity, damage and failure, utilizes experimentally based tabulated input to define the evolution of plasticity and damage and the initiation of failure as opposed to specifying discrete input parameters such as modulus and strength. The plasticity portion of the orthotropic, three-dimensional, macroscopic composite constitutive model is based on an extension of the Tsai-Wu composite failure model into a generalized yield function with a non-associative flow rule. For the damage model, a strain equivalent formulation is used to allow for the uncoupling of the deformation and damage analyses. In the damage model, a semi-coupled approach is employed where the overall damage in a particular coordinate direction is assumed to be a multiplicative combination of the damage in that direction resulting from the applied loads in various coordinate directions. For the failure model, a tabulated approach is utilized in which a stress or strain based invariant is defined as a function of the location of the current stress state in stress space to define the initiation of failure. Failure surfaces can be defined with any arbitrary shape, unlike traditional failure models where the mathematical functions used to define the failure surface impose a specific shape on the failure surface. In the current paper, the complete development of the failure model is described and the generation of a tabulated failure surface for a representative composite material is discussed.

Impact↗
NASA NTRS1999

A Gas-Actuated Projectile Launcher for High-Energy Impact Testing of Structures

A gas-act,uated penetration device has been developed for high-energy impact testing of structures. The high-energy impact. t,estiiig is for experimental simulation of uncontained engine failures. The non-linear transient finite element, code LS-DYNA3D has been used in the numerical simula.tions of a titanium rectangular blade with a.n aluminum target, plate. Threshold velocities for different combinations of pitch and yaw angles of the impactor were obtained for the impactor-target, t8est configuration in the numerica.1 simulations. Complet,e penet,ration of the target plate was also simulat,ed numerically. Finally, limited comparison of analytical and experimental results is presented for complete penetration of the target by the impactor.

Ambur, Damodar R.↗
NASA NTRS1998

Ground-Based Testing of Replacement Thermal Control Materials for the Hubble Space Telescope

The mechanical and optical properties of the metallized Teflon FEP thermal control materials on the Hubble Space Telescope (HST) have degraded over the nearly seven years the telescope has been in orbit. Given the damage to the outer layer of the multi-layer insulation (MLI) that was apparent during the second servicing mission (SM2), the decision was made to replace the outer layer during subsequent servicing missions. A Failure Review Board was established to investigate the damage to the MLI and identify a replacement material. The replacement material had to meet the stringent thermal requirements of the spacecraft and maintain mechanical integrity for at least ten years. Ten candidate materials were selected and exposed to ten-year HST-equivalent doses of simulated orbital environments. Samples of the candidates were exposed sequentially to low and high energy electrons and protons, atomic oxygen, x-ray radiation, ultraviolet radiation and thermal cycling. Following the exposures, the mechanical integrity and optical properties of the candidates were investigated using Optical Microscopy, Scanning Electron Microscopy (SEM), a Laboratory Portable Spectroreflectometer (LPSR) and a Lambda 9 Spectroreflectometer. Based on the results of these simulations and analyses, the Failure Review Board selected a replacement material and two alternates that showed the highest likelihood of providing the requisite thermal properties and surviving for ten years in orbit.

Townsend, Jacqueline A.↗
NASA NTRS1980

Modeling a maintenance simulation of the geosynchronous platform

A modeling technique used to conduct a simulation study comparing various maintenance routines for a space platform is dicussed. A system model is described and illustrated, the basic concepts of a simulation pass are detailed, and sections on failures and maintenance are included. The operation of the system across time is best modeled by a discrete event approach with two basic events - failure and maintenance of the system. Each overall simulation run consists of introducing a particular model of the physical system, together with a maintenance policy, demand function, and mission lifetime. The system is then run through many passes, each pass corresponding to one mission and the model is re-initialized before each pass. Statistics are compiled at the end of each pass and after the last pass a report is printed. Items of interest typically include the time to first maintenance, total number of maintenance trips for each pass, average capability of the system, etc.

Kleiner, A. F., Jr.↗
NASA NTRS1975

Operations analysis (study 2.1): Program manual and users guide for the LOVES computer code

Information is provided necessary to use the LOVES Computer Program in its existing state, or to modify the program to include studies not properly handled by the basic model. The Users Guide defines the basic elements assembled together to form the model for servicing satellites in orbit. As the program is a simulation, the method of attack is to disassemble the problem into a sequence of events, each occurring instantaneously and each creating one or more other events in the future. The main driving force of the simulation is the deterministic launch schedule of satellites and the subsequent failure of the various modules which make up the satellites. The LOVES Computer Program uses a random number generator to simulate the failure of module elements and therefore operates over a long span of time typically 10 to 15 years. The sequence of events is varied by making several runs in succession with different random numbers resulting in a Monte Carlo technique to determine statistical parameters of minimum value, average value, and maximum value.

Wray, S. T., Jr.↗
NASA NTRS1988

An Investigation of the Ability to Recover from Transients Following Failures for Single-Pilot Rotorcraft

A moving-base simulation was conducted to investigate a pilot's ability to recover from transients following single-axis hard-over failures of the flight-control system. The investigation was performed in conjunction with a host simulation that examined the influence of control modes on a single pilot's ability to perform various mission elements under high-workload conditions. The NASA Ames large-amplitude-motion Vertical Motion Simulator (VMS) was utilized, and the experimental variables were the failure axis, the severity of the failure, and the airspeed at which the failure occurred. Other factors, such as pilot workload and terrain and obstacle proximity at the time of failure, were kept as constant as possible within the framework of the host simulation task scenarios. No explicit failure warnings were presented to the pilot. Data from the experiment are shown, and pilot ratings are compared with the proposed handling-qualities requirements for military rotorcraft. Results indicate that the current proposed failure transient requirements may need revision.

Mansur, M. Hossein↗