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Topic: Creep (failure mode)


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In the News (Wed 22 May 19)

  
  Creep (deformation) - Wikipedia, the free encyclopedia
Creep is the term used to describe the tendency of a material to move or to deform permanently to relieve stresses.
Creep is not necessarily a failure mode, but is instead a damage mechanism.
Creep arises from this because of the phenomenon of dislocation climb.
en.wikipedia.org /wiki/Creep_(deformation)   (1786 words)

  
 LJ Gibson Trabecular Bone
In an attempt to determine the phase (collagen or hydroxy-apatite) responsible for these similar creep behaviors, we investigated the creep behavior of demineralized cortical bone, recognizing that the organic (i.e., demineralized) matrix of both cortical and trabecular bone is composed primarily of type I collagen.
The creep behavior was characterized by the three classical stages of decreasing, constant, and increasing creep rates at all applied normalized stresses and temperatures.
Creep failure was also studied using a single cell analysis, in which a closed-form solution was obtained after prescribing the creep properties of the trabeculae.
web.mit.edu /dmse/csg/TBone.htm   (1308 words)

  
 Engineering Example Cases - O'Donnell Consulting
The failure was due to gross plastic deformation of the material in the bend, which had been deformed during fabrication.
A failure specimen was examined, and it was determined that the cracking was due to fatigue.
Creep and tensile instability were identified as the limiting mode of failure.
www.odonnellconsulting.com /examples.html   (3713 words)

  
 Review and Analysis of Lead-Free Solder Material Properties: Sn-Pb Properties and Models
Creep data was obtained from curves of isothermal creep strain versus time under constant applied torques.
One last important aspect of Wong's steady state creep model is that it was derived based on the correlation of creep data from several independent sources, with the correlation holding over a wide range of temperatures (-60°C to 150°C), stresses and creep rates.
and the shear strain increases by creep (increment
www.metallurgy.nist.gov /solder/clech/Sn-Pb_Creep.htm   (3115 words)

  
 Annex B
It is a pre-condition of the use of this clause that all regions which are creep crack critical are accessible for in-service inspection and in-service non-destructive testing, and that instructions for appropriate maintenance and inspection are established and included in the operating instructions.
In the determination of the characteristic values of the material creep strength parameters RM the mean specified material creep strength data shall be used which apply to the materials in the final fabricated condition.
NOTE: This creep design temperature, to be specified for each interval of all load cases in which the calculation temperature is in the creep regime, may be specified as a function of space, or space- independent.
info.tuwien.ac.at /IAA/news/dba_text/creep.htm   (3398 words)

  
 Helen Kane   (Site not responding. Last check: 2007-10-26)
Recently, brittle, intergranular failures of nickel alloy fasteners and bar stock have occurred despite the absence of a hydrogen-producing atmosphere at room temperature.
Further study confirmed that although hydrogen was not involved in these failures, the mode of failure was brittle, intergranular in appearance and exhibited a temperature and rate-dependence [4].
This rate-dependent, intergranular failure mode was observed at temperatures as low as 21o C but became more severe as the temperature increased to the maximum test temperature of 370o C. Traditional loading rate and temperature dependent phenomena known to occur in nickel alloys include hydrogen-assisted cracking, creep and dynamic strain aging (DSA).
www.enme.umd.edu /Natishan/helen.html   (1420 words)

  
 LWR Fuel Pin Performance During Burnup
Newer fuel designs eliminate this failure mode by internally pressurizing the fuel pins with helium and by using sintering techniques which eliminate small pores and increasing the density of the final fuel to around 95% TD, thereby significantly reducing the degree of densification of the fuel.
This mode of failure is referred to as primary hydriding and a rod may be operated for years during the formation of this defect without failure.
Failure of fuel rods may also occur as the result of wear at contacts points between the cladding and the spacer grid caused by flow induced vibrations.
www.nuc.berkeley.edu /thyd/ne161/mspeer/uo2fuel.html   (3967 words)

  
 creep - Hutchinson encyclopedia article about creep   (Site not responding. Last check: 2007-10-26)
In civil and mechanical engineering, the property of a solid, typically a metal, under continuous stress that causes it to deform below its yield point (the point at which any elastic solid normally stretches without any increase in load or stress).
Lead, tin, and zinc, for example, exhibit creep at ordinary temperatures, as seen in the movement of the lead sheeting on the roofs of old buildings.
It is the same woman, I know, for she is always creeping, and most women do not creep by daylight.
encyclopedia.farlex.com /creep   (245 words)

  
 Stress and its effect on materials
Failure by fatigue is the result of processes of crack nucleation and growth, or, in the case of components which may contain a crack introduced during manufacture, the result of crack growth only brought about by the application of cyclical stresses.
Creep is observed in all material types – in metals it only becomes important at temperatures greater than about 0.4Tm (where Tm is the melting point in Kelvin).
A third mode of failure is caused by the presence of ‘stress raisers’.
www.ami.ac.uk /courses/topics/0124_seom   (2265 words)

  
 Problem Outline
Using your result from Problem 3, you may reach the conclusion that beam deflection is related to the potential failure of hyperbaric windows or you may conclude that beam failure is not related to deflection.
This is the mode students are to reason as the most likely failure mode.
Creep is not related to the most likely failure mechanism.
ethics.tamu.edu /Nsfcases/meen/7/mech07.htm   (994 words)

  
 WOLFGANG G. KNAUSS   (Site not responding. Last check: 2007-10-26)
Both structural creep as well as time-dependent fracture are governed by the high temperature viscoelastic behavior of the matrix material.
To gain insight into the fatigue failure process, the development of microscopic energy absorption processes are studied at the tip of propagating cracks through the development of "crazes".
Failure is then the result of the coalescence of these microflaws into a macroscopic fracture.
www.solids.caltech.edu /~wgk   (1001 words)

  
 Landslide Types and Processes
Creep: Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock.
There are generally three types of creep: (1) seasonal, where movement is within the depth of soil affected by seasonal changes in soil moisture and soil temperature; (2) continuous, where shear stress continuously exceeds the strength of the material; and (3) progressive, where slopes are reaching the point of failure as other types of mass movements.
Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridges (fig.
pubs.usgs.gov /fs/2004/3072/fs-2004-3072.html   (2256 words)

  
 MFPT Training Courses Page   (Site not responding. Last check: 2007-10-26)
Failure analysis is a critical first step in identifying a problem that has occurred in a component of a machine or structure.
Once the mode of failure has been identified, appropriate corrective measures may then be taken to try to prevent similar future failures.
Creep failure characteristics, properties and rates, elevated temperature fatigues, thermal and thermomechanical fatigue, metallurgical instabilities, environmentally-assisted, elevated temperature failure, case histories
www.mfpt.org /TC_FailureAna.htm   (774 words)

  
 MEMS and Reliability
Many MEMS device failures are introduced in the fabrication process, and many failure modes in operation are related to the fabrication process.
Conventional failure modes such as fatigue induced fracture did not occur, indicating that the devices are mechanically extremely robust.
Precursors to failure are observed, enabling further understanding of the microscopic changes that occur in the sliding surfaces that ultimately lead to failure.
www.ece.cmu.edu /~koopman/des_s99/mems/index.html   (5368 words)

  
 Failure Analysis
The failures can also be tragic on a monumental scale, as in the case of a wide body aircraft which suffered an engine departure on take-off ("engine departure" is a euphemism for an engine falling off).
Because engineering failures can be so costly in terms of human suffering and financial losses, parties harmed by a failure often seek recompense for their damages.
Possible failure scenarios included: roughening of the surface with rough spots acting as fatigue initiation sites; heat damage due to friction between the workpiece and the beads; solid metal embrittlement due to lead and cadmium in recycled blasting media.
www.matscieng.sunysb.edu /disaster/fail-anal/index.html   (1719 words)

  
 Failure Analysis - Structural Analysis, Inc.
Failure Analysis as applied to the Mechanics and Thermodynamics of Structures is the investigative procedure involved in determination of the cause and effect that results in failure of a mechanical system to function as designed.
The failure mode can be complete and catastrophic structural failure or, simply, failure to meet specified design goals.
Failure analysis is often used to develop the background necessary for expert testimony.
www.sai-mtab.com /consulting/failure.htm   (114 words)

  
 Structural failure - Wikipedia, the free encyclopedia
Structural failure refers to loss of the load-carrying capacity of a component or member within the structure or of the structure itself.
Structural failure is initiated when the material is stressed to its strength limit, thus causing fracture or excessive deformations.
Ultimate failure strength is one of the limit states that must be accounted for in civil engineering.
en.wikipedia.org /wiki/Structural_failure   (269 words)

  
 R&T Articles Submission Form
The creep life of a component is discretized into short time steps, during which the stress distribution is assumed constant.
Failure is assumed to occur when the normalized cumulative damage at any point in the component reaches unity.
In this theory, the uniaxial creep rate is described in terms of stress, temperature, time, and the current state of material damage.
www.grc.nasa.gov /WWW/RT1997/5000/5920powers.htm   (489 words)

  
 Disposable article construction adhesive - Patent 5057571
In sharp contrast to bond elastic materials to substrates, a different adhesive is currently used that primarily exhibits high creep resistance to ensure that the elastic, when under stress, does not move relative to the surface of the substrate or become partially or fully detached.
The dynamic peel adhesion test indicates that the Schmidt adhesive bond between nonwoven and polyethylene is subject to adhesive failure, while the adhesive of the invention maintains the integrity of the bond until the substrate itself fails.
With respect to elastic attachment properties, Example A and Example B have a creep failure of the elastic attachment of 77.5% and 71%, respectively, indicating that the elastic once bonded to the polyethylene backing sheet could lose a substantial proportion of its stretch during use.
www.freepatentsonline.com /5057571.html   (8203 words)

  
 DC   (Site not responding. Last check: 2007-10-26)
The failure mode was identical to one experienced in the MTR28 style at NASA GSFC in 2000.
The case lid had flexed away from the case in a vacuum environment due to the pressure differential between the inside of the hermetically sealed part and the pressure of the vacuum outside of the part.
Past part failures have occurred due to tension and shear extended to a weakened join in unexpected ways such as due to self-heating induced temperature cycling and externally imposed electric fields.
nepp.nasa.gov /dcdc/packagingandworkmanship.htm   (1205 words)

  
 APTECH engineering analysis and computer modeling services for machinery and equipment failures, forensic ...
During the failure investigation process, the first step is a visit to the incident site to gather facts and evidence relevant to the failure and to document the appearance of the site.
The first is to provide an initial screening of potential failure modes and the second is to serve as a check on later more sophisticated, and expensive, computer models (finite element or finite difference).
In some cases the results from the closed form analytical approach are sufficient to pin down the failure mode.
www.failure-analysis-consultant.com /analysis_and_modeling.html   (554 words)

  
 Failure Analysis Capability Brief
Lack of fusion, weld defect: Determined the cause of failure to be improper welding parameters, resulting in insufficient melting of weld wire and subsequent cracking.
Reverse-bending fatigue: Failure of stainless-steel screws was caused by repeated reverse-bending stresses.
Pin-vibration failure: Cu-Be microelectronic connector-pin failures were found to be caused by fatigue and possible misalignment during vibration testing.
www.sandia.gov /materials/sciences/factsheets/FailureAnalysis.html   (639 words)

  
 ENGR322 Final Exam S06
Examine the pairs of photographs of fracture surfaces and compare them in terms of (i) the type of failure (ductile, brittle, fatigue, or a combination), and (ii) what features you used to answer part (i).
It is easily identified by the cup and cone fracture, and shows a fibrous fracture surface indicative of the ductile deformation at the fracture surface.
This sample is 75-80% brittle failure, and the rest is ductile.
oregonstate.edu /instruct/engr322/Exams/S06/ENGR322-Final.html   (2081 words)

  
 MAGNET WIRE CONNECTIONS IN TRANSFORMERS
The reasons for this loosening tendency are a combination of vibration, cold flow or creep of the materials, and repeated expansion and contraction of the connection due to load cycle changes, and ambient temperature changes.
The areas most prone to failure with this type of connector are moving equipment, such as motors, and their related driven equipment which due to the motion are subject to mechanical shock and vibrations.
This “Spring Compression” assures that the initial pressure obtained in the self crimping process, is retained throughout the life of the connection, and compensates for thermal expansion and contraction, conductor cold flow, and vibration.
www.cytolok.com /Robin_Tech2.htm   (3465 words)

  
 BEAR Inc. - Metallurgy
The turbine blade in the photograph at right, for example, cracked due to creep (creep is deformation of a material subjected to tensile stresses at high temperature).
In this case, BEAR was asked to determine whether shaft failure was the cause of an accident.
This failure, like many others that BEAR engineers have analyzed, was resolved simply by examining the fracture and interpreting what the features meant.
www.bearinc.com /metallurgy.html   (572 words)

  
 CTL-Failure Analysis
However, without properly characterizing the failure attributes, corrosion debris, or environment involved in the failure, the root cause of the failure may be coming from an unexpected source, and may remain to cause the replacement components to fail.
Failure analysis and consultation for water side denickelification of copper-nickel heat exchanger tubes in a reformate bottoms column.
Failure analysis of HIC in a depentanizer condenser heat exchanger shell.
www.corrosionlab.com /failure-analysis.htm   (1702 words)

  
 Stylus 710 > Frequently Asked Questions
Shooting modes govern what type of data (still image or movie) is recorded and what camera functions and settings are used to capture it.
To select a mode, turn the mode dial so that the appropriate icon or text is aligned with the LED light to the left of the dial.
Digital Image Stabilization mode (Hand icon): The camera automatically boosts ISO sensitivity and shutter speed as necessary in order to capture clear, bright images in low light or when the camera or subject is in motion at the time of image capture.
www.olympusamerica.com /cpg_section/cpg_support_faqs.asp?id=1224   (9252 words)

  
 Maintaining Normal Force in Electrical Connections
This economic decision brought with it a different failure mode than previously experienced: “creep” induced loosening of the bolted connection.
Some creep is expected as the joint heats up and cools down with use.
As the creep rate increases, the joint loosens and the temperature increases until you are left with a corroded connection.
www.mt-online.com /articles/0603cook.cfm   (707 words)

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