Erosion Resistance and Failure Mechanisms of Several Nozzle Materials in a Small Solid-Propellant Rocket Engine
Erosion resistance and failure mechanisms of nozzle materials in small solid-propellant rocket engine
ROCKET NOZZLE↗
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Investigation of static and cyclic bearing failure mechanisms for GR/EP laminates
Static, cyclic load (fatigue), and residual strength testing of graphite-epoxy (GR/EP) and aluminum pin bearing joints was completed to study bearing failure mechanisms. Parameters investigated included static strength, failure mode, fatigue life, hole growth, joint stiffness, and residual strength. Comparative evaluation of these results show that the MIL-HDBK-5 convention for the definition of bearing strength can be used for GR/EP materials while maintaining the same, or improved, level of structural integrity shown for metal joints.
Walter, R. W.↗
Some Aspects of the Failure Mechanisms in BaTiO3-Based Multilayer Ceramic Capacitors
The objective of this presentation is to gain insight into possible failure mechanisms in BaTiO3-based ceramic capacitors that may be associated with the reliability degradation that accompanies a reduction in dielectric thickness, as reported by Intel Corporation in 2010. The volumetric efficiency (microF/cm3) of a multilayer ceramic capacitor (MLCC) has been shown to not increase limitlessly due to the grain size effect on the dielectric constant of ferroelectric ceramic BaTiO3 material. The reliability of an MLCC has been discussed with respect to its structure. The MLCCs with higher numbers of dielectric layers will pose more challenges for the reliability of dielectric material, which is the case for most base-metal-electrode (BME) capacitors. A number of MLCCs manufactured using both precious-metal-electrode (PME) and BME technology, with 25 V rating and various chip sizes and capacitances, were tested at accelerated stress levels. Most of these MLCCs had a failure behavior with two mixed failure modes: the well-known rapid dielectric wearout, and so-called 'early failures." The two failure modes can be distinguished when the testing data were presented and normalized at use-level using a 2-parameter Weibull plot. The early failures had a slope parameter of Beta >1, indicating that the early failures are not infant mortalities. Early failures are triggered due to external electrical overstress and become dominant as dielectric layer thickness decreases, accompanied by a dramatic reduction in reliability. This indicates that early failures are the main cause of the reliability degradation in MLCCs as dielectric layer thickness decreases. All of the early failures are characterized by an avalanche-like breakdown leakage current. The failures have been attributed to the extrinsic minor construction defects introduced during fabrication of the capacitors. A reliability model including dielectric thickness and extrinsic defect feature size is proposed in this presentation. The model can be used to explain the Intel-reported reliability degradation in MLCCs with respect to the reduction of dielectric thickness. It can also be used to estimate the reliability of a MLCC based on its construction and microstructure parameters such as dielectric thickness, average grain size, and number of dielectric layers. Measures for preventing early failures are also discussed in this document.
Liu, David Donhang↗
Compression failure mechanisms of single-ply, unidirectional, carbon-fiber composites
A single-ply composite compression test was used to study compression failure mechanisms as a function of fiber type, matrix type, and interfacial strength. Composites made with low- and intermediate-modulus fibers (Hercules AS4 and IM7) in either an epoxy (Hercules 3501-6) or a thermoplastic (ULTEM and LARC-TPI) matrix failed by kink banding and out-of-plane slip. The failures proceeded by rapid and catastrophic damage propagation across the specimen width. Composites made with high-modulus fibers (Hercules HMS4/3501-6) had a much lower compression strength. Their failures were characterized by kink banding and longitudinal splitting. The damage propagated slowly across the specimen width. Composites made with fibers treated to give low interfacial strength had low compression strength. These composites typically failed near the specimen ends and had long kink bands.
Ha, Jong-Bae↗
The failure mechanism of a nickel electrode in a nickel-hydrogen cell
Studies on a number of types of nickel electrodes after cycle failure in a Ni/H2 cell showed that the failure is due to the loss of high rate discharge capability rather than an absolute capacity loss. The failure mechanism is speculated to be a combination of migration of the active material away from the current collecting nickel sinter, increased porosity of the active material caused by cycling, and an electrical isolation process of the active material during discharge.
Lim, H. S.↗
Deformation and failure mechanisms of graphite/epoxy composites under static loading
The mechanisms of deformation and failure of graphite epoxy composites under static loading were clarified. The influence of moisture and temperature upon these mechanisms were also investigated. Because the longitudinal tensile properties are the most critical to the performance of the composite, these properties were investigated in detail. Both ultimate and elastic mechanical properties were investigated, but the study of mechanisms emphasized those leading to failure of the composite. The graphite epoxy composite selected for study was the system being used in several NASA sponsored flight test programs.
Clements, L. L.↗
Analyses of Failure Mechanisms and Residual Stresses in Graphite/Polyimide Composites Subjected to Shear Dominated Biaxial Loads
This research contributes to the understanding of macro- and micro-failure mechanisms in woven fabric polyimide matrix composites based on medium and high modulus graphite fibers tested under biaxial, shear dominated stress conditions over a temperature range of -50 C to 315 C. The goal of this research is also to provide a testing methodology for determining residual stress distributions in unidirectional, cross/ply and fabric graphite/polyimide composites using the concept of embedded metallic inclusions and X-ray diffraction (XRD) measurements.
Kumosa, M.↗
Product Reliability Trends, Derating Considerations and Failure Mechanisms with Scaled CMOS
As microelectronics is scaled into the deep sub-micron regime, space and aerospace users of advanced technology CMOS are reassessing how scaling effects impact long-term product reliability. The effects of electromigration (EM), time-dependent-dielectric-breakdown (TDDB) and hot carrier degradation (HCI and NBTI) wearout mechanisms on scaled technologies and product reliability are investigated, accelerated stress testing across several technology nodes is performed, and FA is conducted to confirm the failure mechanism(s).
CMOS integrated circuits↗
Field failure mechanisms for photovoltaic modules
Beginning in 1976, Department of Energy field centers have installed and monitored a number of field tests and application experiments using current state-of-the-art photovoltaic modules. On-site observations of module physical and electrical degradation, together with in-depth laboratory analysis of failed modules, permits an overall assessment of the nature and causes of early field failures. Data on failure rates are presented, and key failure mechanisms are analyzed with respect to origin, effect, and prospects for correction. It is concluded that all failure modes identified to date are avoidable or controllable through sound design and production practices.
Dumas, L. N.↗
Failure mechanics in low-velocity impacts on thin composite plates
Eight-ply quasi-isotropic composite plates of Thornel 300 graphite in Narmco 5208 epoxy resin (T300/5208) were tested to establish the degree of equivalence between low-velocity impact and static testing. Both the deformation and failure mechanics under impact were representable by static indentation tests. Under low-velocity impacts such as tool drops, the dominant deformation mode of the plates was the first, or static, mode. Higher modes are excited on contact, but they decay significantly by the time the first-mode load reaches a maximum. The delamination patterns were observed by X-ray analysis. The areas of maximum delamination patterns were observed by X-ray analysis. The areas of maximum delamination coincided with the areas of highest peel stresses. The extent of delamination was similar for static and impact tests. Fiber failure damage was established by tensile tests on small fiber bundles obtained by deplying test specimens. The onset of fiber damage was in internal plies near the lower surface of the plates. The distribution and amount of fiber damage was similar fo impact and static tests.
Elber, W.↗
Lubrication and failure mechanisms of molybdenum disulfide films. 1: Effect of atmosphere
Friction, wear, and wear lives of rubbed molybdenum disulfide (MoS2 films applied to sanded 440C HT steel surfaces were evaluated in moist air, dry air, and dry argon. Optical microscope observations were made as a function of sliding distance to determine the effect of moisture and oxygen on the lubricating and failure mechanisms of MoS2 films. In general, the lubrication process consisted of the formation of a thin, metallic colored, coalesced film of MoS2 that flowed between the surfaces in relative motion. In air, failure was due to the transformation of the metallic colored, coalesced films to a black, powdery material. Water in the air appeared to accelerate the transformation rate. In argon, no transformation of MoS2 was observed with the microscope, but cracking and spalling of the coalesced film occurred and resulted in the gradual depletion of the film.
Fusaro, R. L.↗
A combined experimental and finite element study to predict the failure mechanisms in SiC coated carbon/carbon composites at room and elevated temperatures under flexural loading
Response of quasi-isotropic laminates of SiC coated Carbon/Carbon (C/C) composites have been investigated under flexural loading at various temperatures. Variation of load-deflection behavior with temperatures are studied. Increase in flexural strength and stiffness are observed with the rise in temperature. Extensive analyses through Optical Microscope (OM) and Non-Destructive Evaluation (NDE) have been performed to understand the failure mechanisms. Damage zone is found only within the neighborhood of the loading plane. Isoparametric layered shell elements developed on the basis of the first order shear deformation theory have been used to model the thin laminates of C/C under flexural loading. Large deformation behavior has been considered in the finite element analysis to account for the non-linearities encountered during the actual test. Data generated using finite element analysis are presented to corroborate the experimental findings, and a comparison in respect of displacement and stress-strain behavior are given to check the accuracy of the finite element analysis. Reasonable correlation between the experimental and finite element results have been established.
Mahfuz, Hassan↗
Failure mechanisms of 3-D woven SiC/SiC composites under tensile and flexural loading at room and elevated temperatures
Nicalon silicon carbide 3D yarn with silicon carbide matrix composites made through a chemical vapor infiltration (CVI) process were investigated under tensile and flexural loading at 23, 1200 and 1550 C in air. The effectiveness of a chemical vapor deposition (CVD) SiC surface coating was also evaluated in severe oxidizing environment. Acoustic emission sensors and in situ optical microscopy were used at room temperature to monitor the failure mechanisms. It is shown that the level of tensile stress at which nonlinear behavior begins is not drastically reduced at 1200 and 1550 C when composites were protected by a SiC surface coating. Extensive fiber pull-out was observed only in the 1550 C specimen. Similar behaviors were also found in flexural specimens.
Chulya, Abhisak↗
Cyclic Failure Mechanisms of Thermal and Environmental Barrier Coating Systems Under Thermal Gradient Test Conditions
Plasma-sprayed ZrO2-8wt%Y2O3 and mullite+BSAS/Si multilayer thermal and environmental barrier coating (TBC-EBC) systems on SiC/SiC ceramic matrix composite (CMC) substrates were thermally cyclic tested under high thermal gradients using a laser high-heat-flux rig in conjunction with furnace exposure in water-vapor environments. Coating sintering and interface damage were assessed by monitoring the real-time thermal conductivity changes during the laser heat-flux tests and by examining the microstructural changes after exposure. Sintering kinetics of the coating systems were also independently characterized using a dilatometer. It was found that the coating failure involved both the time-temperature dependent sintering and the cycle frequency dependent cyclic fatigue processes. The water vapor environments not only facilitated the initial coating conductivity increases due to enhanced sintering and interface reaction, but also promoted later conductivity reductions due to the accelerated coating cracking and delamination. The failure mechanisms of the coating systems are also discussed based on the cyclic test results and are correlated to the sintering and thermal stress behavior under the thermal gradient test conditions.
Zhu, Dongming↗
Creep/Stress Rupture Behavior and Failure Mechanisms of Full CVI and Full PIP SiC/SiC Composites at Elevated Temperatures in Air
SiC/SiC composites fabricated by melt infiltration are being considered as potential candidate materials for next generation turbine components. However these materials are limited to 2400 F application because of the presence of residual silicon in the SiC matrix. Currently there is an increasing interest in developing and using silicon free SiC/SiC composites for structural aerospace applications above 2400 F. Full PIP or full CVI or CVI + PIP hybrid SiC/SiC composites can be fabricated without excess silicon, but the upper temperature stress capabilities of these materials are not fully known. In this study, the on-axis creep and rupture properties of the state-of-the-art full CVI and full PIP SiC/SiC composites with Sylramic-iBN fibers were measured at temperatures to 2700 F in air and their failure modes examined. In this presentation creep rupture properties, failure mechanisms and upper temperature capabilities of these two systems will be discussed and compared with the literature data.
Creep Durability↗
Effects of Board Surface Finish on Failure Mechanisms and Reliability of BGAs
This paper will present cycles to failure in Weibull plots as well as their failure characteristics up to 7000 cycles.
Ball Grid Array (BGA) failure mechanisms assembly ↗
Deformation and failure mechanisms in metal matrix composites
An investigation was undertaken to determine the key deformation mechanisms and their interaction leading to failure of both 0 degree and 90 degree Ti 15-3/SCS-6 laminae under monotonic loading. The experimental results suggest that inelastic deformation in the 0-degree lamina is dominated by plastic deformation and that in the 90-degree lamina is dominated by both fiber-matrix debonding and plasticity. The loading-unloading response, monitoring of Poisson's ratio and microscopy were utilized to identify the key deformation mechanisms. The sequence of deformation mechanisms leading to failure are identified for both the 0 and the 90-degree specimens. The threshold strains for plasticity or damage which are referred to as 'microdeformation' in the 0 deg and 90 deg laminae are approximately 0.004 and 0.002, respectively, at room temperature. These strain levels may be considered critical in initiation based structural design with these composites.
Newaz, G.↗
Mechanical failure probability of glasses in Earth orbit
Results of five years of earth-orbital exposure on mechanical properties of glasses indicate that radiation effects on mechanical properties of glasses, for the glasses examined, are less than the probable error of measurement. During the 5 year exposure, seven micrometeorite or space debris impacts occurred on the samples examined. These impacts were located in locations which were not subjected to effective mechanical testing, hence limited information on their influence upon mechanical strength was obtained. Combination of these results with micrometeorite and space debris impact frequency obtained by other experiments permits estimates of the failure probability of glasses exposed to mechanical loading under earth-orbit conditions. This probabilistic failure prediction is described and illustrated with examples.
Kinser, Donald L.↗