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Results for “crack damage”

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.

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At least 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Spiral Bevel Pinion Crack Detection in a Helicopter Gearbox

The vibration resulting from a cracked spiral bevel pinion was recorded and analyzed using existing Health and Usage Monitoring System (HUMS) techniques. A tooth on the input pinion to a Bell OH-58 main rotor gearbox was notched and run for an extended period at severe over-torque condition to facilitate a tooth fracture. Thirteen vibration-based diagnostic metrics were calculated throughout the run. After 101.41 hours of run time, some of the metrics indicated damage. At that point a visual inspection did not reveal any damage. The pinion was then run for another 12 minutes until a proximity probe indicated that a tooth had fractured. This paper discusses the damage detection effectiveness of the different metrics and a comparison of effects of the different accelerometer locations.

Decker, Harry J.↗
NASA NTRS2017

Small Particle Impact Damage on Different Glass Substrates

Impact experiments using sand particles were performed on four distinct glass substrates. The sand particles were characterized using the X-Ray micro-CT technique; 3-D reconstruction of the particles was followed by further size and shape analyses. High-speed video footage from impact tests was used to calculate the incoming and rebound velocities of the individual sand impact events, as well as particle volume. Further, video analysis was used in conjunction with optical and scanning electron microscopy to relate the incoming velocity and shape of the particles to subsequent fractures, including both radial and lateral cracks. Analysis was performed using peridynamic simulations.

Waxman, R.↗
NASA NTRS1989

Torsional and biaxial (tension-torsion) fatigue damage mechanisms in Waspaloy at room temperature

Strain controlled torsional and biaxial (tension-torsion) low cycle fatigue behavior of Waspaloy was studied at room temperature as a function of heat treatment. Biaxial tests were conducted under proportional and nonproportional cyclic conditions. The deformation behavior under these different cyclic conditions was evaluated by slip trace analysis. For this, a Schmidt-type factor was defined for multiaxial loading conditions, and it was shown that when the slip deformation is predominant, nonproportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under nonproportional cyclic conditions, deformation was through multiple slip, as opposed to single slip for other loading conditions, which gave rise to increased hardening. The total life for a given test condition was found to be independent of heat treatment. This was interpreted as being due to the differences in the cycles to initiation and propagation of cracks.

Jayaraman, N.↗
NASA NTRSDate not supplied

Challenges in Scaling Analysis from Coupons to Elements in 3D Woven Composites for a Launch Vehicle End-Ring Structure

The limitations of structural design with 3D woven composites based on homogenized material models characterized using coupon test data, representative unit cell analysis, or a combination of the two are discussed in the context of a space launch system (SLS)-scale end ring. Selected building block test configurations at the coupon, element, and subcomponent scales are described in detail. Highly instrumented tests and X-ray computed tomography inspections are used to characterize the structural behavior and associated damage progression with increasing load. It is shown that a single homogenized material constitutive relationship, applied at coupon and element scale, is not sufficient to model the structural response observed in both tests. In fact, substantially different stress-strain laws are required to predict the response of the coupon and element scale specimens, despite similar loading conditions. A model with discrete representation of the binder tows and cohesive interfaces to model matrix cracking shows much better agreement with the test data at the two length scales. Thus, evidence is provided showing that predictive structural analysis of 3D woven composites requires discrete representation of the tows, matrix cracking morphology, and their interactions in the structural configuration. With accurate knowledge of the element scale behavior, engineering approximations readily enable analysis scale-up to the subcomponent level.

Andrew C Bergan↗
DOE OSTI2022

Damage of prismatic lithium‐ion cells subject to bending: Test, model, and detection

Abstract The mechanically induced internal short circuit (ISC) is one of the major safety concerns of lithium‐ion batteries. Mechanical abuse tests are often performed to evaluate the integrity and safety of lithium‐ion batteries under mechanical loadings. Except for the widely explored compression‐dominated indentation tests, bending is another typical real‐world loading condition that is tension‐dominated. To investigate the mechanical damage and ISC behavior of batteries under bending, we carried out controlled three‐point bending tests in four progressive steps on prismatic battery cells with maximum deflections ranging from 38% to 76% of the cell thickness. None of the tested cells experienced an ISC. We then conducted 3D X‐ray computed tomography (CT) scanning on the bent cells after unloading. X‐ray CT images showed three out of the four tested cells have extensive cracking in the electrode layers at the bottom side (opposite to the loading head). This indicates that cracking does not necessarily lead to an ISC under bending. Electrochemical impedance spectroscopy was also measured on the bent cells and substantial changes were observed. Both the bulk resistance and charge‐transfer resistance increased significantly after bending, which could influence the battery performance and lifespan. We then developed a detailed finite (FE) element model to further investigate the mechanical deformation and failure mechanisms. The FE model successfully predicts the load–displacement response and reproduces the deformation patterns. The findings and the FE model developed in the present study provide useful insights and tools for the battery structure and crash safety design. image

25 ENERGY STORAGE↗
NASA NTRS1982

Dynamics and mechanism of cavitation erosion on perspex and epoxy resins tested in a rotating disk device

The cavitation erosion behavior including the initiation, dynamics and mechanism of damage process on perspex and epoxy resin specimens tested in a rotating disk device were discussed with respect to exposure time. The inception of erosion always took place at the location nearest to the center of rotation of the disk. Subsequently, as exposure time increased, erosion initiated at other locations as well. Light optical photographs and scanning electron micrographs clearly indicate that most of the material loss appears to occur form the networks of cracks due to their interaction and pits indicate particle debris. The optical degradation (loss of transmittance) on perspex was observed to be more on the rear side than on the front side.

Rao, P. V.↗
NASA NTRS1983

Cavitation erosion characteristics of poly(methyl methacrylate) in a rotating disk device

The cavitation erosion behavior including the initiation, dynamics and mechanism of damage process on perspex and epoxy resin specimens tested in a rotating disk device were discussed with respect to exposure time. The inception of erosion always took place at the location nearest to the center of rotation of the disk. Subsequently, as exposure time increased, erosion initiated at other locations as well. Light optical photographs and scanning electron micrographs clearly indicate that most of the material loss appears to occur form the networks of cracks due to their interaction and pits indicate particle debris. The optical degradation (loss of transmittance) on perspex was observed to be more on the rear side than on the front side. Previously announced in STAR as N83-11329

Veerabhadra Rao, P.↗
NASA NTRS1984

Hygrothermal influence on delamination behavior of graphite/epoxy laminates

The hygrothermal effect on the fracture behavior of graphite-epoxy laminates was investigated to develop a methodology for damage tolerance predictions in advanced composite materials. Several T300/934 laminates were tested using a number of specimen configurations to evaluate the effects of temperature and humidity on delamination fracture toughness under mode 1 and mode 2 loading. It is indicated that moisture has a slightly beneficial influence on fracture toughness or critical strain energy release rate during mode 1 delamination, but has a slightly deleterious effect on mode 2 delamination and mode 1 transverse cracking. The failed specimens are examined by SEM and topographical differences due to fracture modes are identified. It is concluded that the effect of moisture on fracture topography can not be distinguished.

Garg, A.↗
NASA NTRS1985

Hygrothermal influence on delamination behavior of graphite/epoxy laminates

The hygrothermal effect on the fracture behavior of graphite-epoxy laminates was investigated to develop a methodology for damage tolerance predictions in advanced composite materials. Several T300/934 laminates were tested using a number of specimen configurations to evaluate the effects of temperature and humidity on delamination fracture toughness under mode 1 and mode 2 loading. It is indicated that moisture has a slightly beneficial influence on fracture toughness or critical strain energy release rate during mode 1 delamination, but has a slightly deleterious effect on mode 2 delamination, and mode 1 transverse cracking. The failed specimens are examined by SEM and topographical differences due to fracture modes are identified. It is concluded that the effect of moisture on fracture topography can not be distinguished.

Garg, A.↗
NASA NTRS1990

Microstructure: Property correlation

Strain controlled torsional and biaxial (tension-torsion) low cycle fatigue behavior of Waspaloy was studied at room temperature as a function of heat treatment. Biaxial tests were conducted under proportional (when the axial and torsional strain cycles are in-phase) and non-proportional (when the axial and torsional strain cycles are 90 deg out-of-phase) cyclic conditions. The deformation behavior under these different cyclic conditions were evaluated by slip trace analysis. For this, a Schmidt-type factor was defined for multiaxial loading conditions and it was shown that when the slip deformation is predominant, non-proportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under non-proportional cyclic conditions, deformation was through multiple slip as opposed single slip for other loading conditions, which gave rise to increased hardening. The total life for a given test condition was found to be independent of heat treatment. This was interpreted as being due to the differences in the cycles to initiation and propagation of cracks.

Jayaraman, N.↗
NASA NTRS1993

Modelling hypervelocity impacts into aluminum structures based on LDEF data

Realizing and understanding the effects of the near-Earth space environment on a spacecraft during its mission lifetime is becoming more important with the regeneration of America's space program. Included among these potential effects are the following: erosion and surface degradation due to atomic oxygen impingement; ultraviolet exposure embrittlement; and delamination, pitting, cratering, and ring formation due to micrometeoroid and debris impacts. These effects may occur synergistically and may alter the spacecraft materials enough to modify the resultant crater, star crack, and/or perforation. This study concentrates on modelling the effects of micrometeoroid and debris hypervelocity impacts into aluminum materials (6061-T6). Space debris exists in all sizes, and has the possibility of growing into a potentially catastrophic problem, particularly since self-collisions between particles can rapidly escalate the number of small impactors. We have examined the morphologies of the Long Duration Exposure Facility (LDEF) impact craters and the relationship between the observed impact damage on LDEF versus the existing models for both the natural (micrometeoroid) and manmade (debris) environments in order to better define these environments.

Coombs, C. R.↗
NASA NTRS2005

Structural Health Monitoring of Composite Plates Under Ambient and Cryogenic Conditions

Methods for structural health monitoring are now being assessed, especially in high-performance, extreme environment, safety-critical applications. One such application is for composite cryogenic fuel tanks. The work presented here attempts to characterize and investigate the feasibility of using imbedded piezoelectric sensors to detect cracks and delaminations under cryogenic and ambient conditions. Different types of excitation and response signals and different sensors are employed in composite plate samples to aid in determining an optimal algorithm, sensor placement strategy, and type of imbedded sensor to use. Variations of frequency and high frequency chirps of the sensors are employed and compared. Statistical and analytic techniques are then used to determine which method is most desirable for a specific type of damage and operating environment. These results are furthermore compared with previous work using externally mounted sensors. More work is needed to accurately account for changes in temperature seen in these environments and be statistically significant. Sensor development and placement strategy are other areas of further work to make structural health monitoring more robust. Results from this and other work might then be incorporated into a larger composite structure to validate and assess its structural health. This could prove to be important in the development and qualification of any 2nd generation reusable launch vehicle using composites as a structural element.

Engberg, Robert C.↗
NASA NTRS1966

X-ray analysis of fatigue damage in copper

A Warren-Averbach x-ray line profile analysis was applied to, broadened x-ray diffraction peaks from copper deformed in fatigue. The copper specimens were fatigued by four point bending at various strain amplitudes, and measurements were made at various fractions of the total fatigue life. The analysis results in an estimation of 1) an average coherently diffracting domain size in a direction normal to the diffracting planes; and 2) a strain distribution function. The strain distribution function is in terms of the root mean square strain, <ϵ^(2)> where ϵ is averaged over a given distance at all points in the diffracting crystals. This rms strain is expressed as a function of averaging distance for a direction normal to the diffracting planes. The rms strains were found to be a function of the fatigue strain amplitude level, increasing with amplitude and reaching a maximum limiting value during the first 2% of the fatigue life. The strains were normally larger in the 4lO0 direction compared to the <111> direction and the absolute values were quite small. These results may be explained by assuming the dislocations are present in the form of dipoles because the lattice strain around a dipole is much less than around single dislocations. Conclusions arrived at in this analysis are in agreement with current theories of fatigue damage in metals. The result that maximum hardening is achieved during the initial few percent of the fatigue life is confirmed by many other investigators using entirely different analytical techniques. It is felt that the structure of the material is changing during this initial hardening stage to an eventual steady state characteristic of the testing conditions. A unique substructure is developed which thereafter persists, and the remainder of the fatigue test is taken up by crack propagation through this substructure until ultimate failure occurs by fracture. The formation of this steady state structure is dependent on the maximum fatigue strain amplitude and on the frequency and temperature of cycling for a particular material.

COPPER↗
NASA NTRS1976

Fatigue damage of notched boron/epoxy laminates under constant amplitude loading

Fatigue damage in (0, + or - 45) and (0, + or - 45,90) boron/epoxy laminates was studied with X-ray radiography and scanning electron microscopy. In addition, limited tests for residual strength and stiffness were performed. The results of this study suggest that in boron/epoxy laminates the 45-degree plies play a key role in the fatigue process of boron/epoxy laminates that contain them. The fatigue process in the + or - 45-degree plies starts as intralaminar matrix cracks.

Roderick, G. L.↗
NASA NTRS2012

Influence of Finite Element Size in Residual Strength Prediction of Composite Structures

The sensitivity of failure load to the element size used in a progressive failure analysis (PFA) of carbon composite center notched laminates is evaluated. The sensitivity study employs a PFA methodology previously developed by the authors consisting of Hashin-Rotem intra-laminar fiber and matrix failure criteria and a complete stress degradation scheme for damage simulation. The approach is implemented with a user defined subroutine in the ABAQUS/Explicit finite element package. The effect of element size near the notch tips on residual strength predictions was assessed for a brittle failure mode with a parametric study that included three laminates of varying material system, thickness and stacking sequence. The study resulted in the selection of an element size of 0.09 in. X 0.09 in., which was later used for predicting crack paths and failure loads in sandwich panels and monolithic laminated panels. Comparison of predicted crack paths and failure loads for these panels agreed well with experimental observations. Additionally, the element size vs. normalized failure load relationship, determined in the parametric study, was used to evaluate strength-scaling factors for three different element sizes. The failure loads predicted with all three element sizes provided converged failure loads with respect to that corresponding with the 0.09 in. X 0.09 in. element size. Though preliminary in nature, the strength-scaling concept has the potential to greatly reduce the computational time required for PFA and can enable the analysis of large scale structural components where failure is dominated by fiber failure in tension.

Satyanarayana, Arunkumar↗
DOE OSTI2020

Corrosion Mitigation and Increased Discharge Capacity in Aqueous Processed Thick Cathodes using Phosphoric Acid Additives

Aqueous processed cathodes for lithium-ion batteries are favorable for both cost and environmental reasons; however, these electrodes still face significant problems with increasing areal capacities (i.e. thickness). Highly basic slurry conditions (pH in excess of 12) corrode the current collector surface and evolve hydrogen gas. Consequently, bubbling at the electrode interface causes substantial damage to the dried electrode. As the loading of these electrodes is increased, damage becomes severe and results in lack of adhesion and cohesion. Here introduction of phosphoric acid to combat the rise in pH and suppress the corrosion at the current collector surface is investigated. Phosphoric acid was added in increments of 0.5, 1.0, and 1.5 wt% and the subsequent effects on slurry rheology, particle size, adhesion, and electrochemical cycling were investigated. A technique is reported for obtaining thick (6-8 mAh/cm2) cathodes that exhibit reduced surface cracking and improved rate performance as compared to control samples.

Kukay, Alexander↗
NASA NTRS1998

Creep Life of Ceramic Components Using a Finite-Element-Based Integrated Design Program (CARES/CREEP)

The desirable properties of ceramics at high temperatures have generated interest in their use for structural application such as in advanced turbine engine systems. Design lives for such systems can exceed 10,000 hours. The long life requirement necessitates subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to creep rupture conditions. This methodology utilizes commercially available finite element packages and takes into account the time-varying creep strain distributions (stress relaxation). The creep life, of a component is discretized into short time steps, during which the stress and strain distributions are assumed constant. The damage is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. Failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity. The corresponding time will be the creep rupture life for that component. Examples are chosen to demonstrate the Ceramics Analysis and Reliability Evaluation of Structures/CREEP (CARES/CREEP) integrated design program, which is written for the ANSYS finite element package. Depending on the component size and loading conditions, it was found that in real structures one of two competing failure modes (creep or slow crack growth) will dominate. Applications to benchmark problems and engine components are included.

Powers, L. M.↗