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金属材料的材料性能要求和相关试验方法

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SME Materials properties requirements and associated testInitiative methods for metallic materials

ESA SME Initiative Course D:Materials

Ton de Rooij Principal Metallurgist Materials and Processes Division Product Assurance and Safety Department

Materials and Processes Division ESA/ESTEC/TOS-QM

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Content of presentation
? ? ? ? ? ? ? ? ? ? ? Materials properties Constraints on materials Surface finishes coatings Joining Corrosion testing Mechanical testing Macroscopic examination Microscopic examination Non-destructive examination Failure analysis
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Materials Properties
? ? ? ? ? ? ? Strength Elastic modulus Fatigue Fracture toughness Creep Micro-yielding Coefficient of thermal expansion and coefficient of moisture expansion Stress corrosion Corrosion fatigue Hydrogen embrittlement

? Wear and fretting ? Surface finishes
– – – – – – Anodising Conversion pickling/etching mechanical

? Coatings
hard barriers

? ? ?

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Metallic Materials used in space
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? ? ? ?

? ? ?

Light metals, such as beryllium, magnesium, aluminium and titanium and their alloys Steels, such as low-alloy, tool, corrosion resistant, precipitation hardable, and maraging Nickel and nickel base alloys, including pure nickel, Monel alloys, Inconel alloys, and other nickel- and cobald-base superalloys Refractory metals, principally niobium and molybdenum Copper-base alloys, including pure coppers, beryllium coppers, bronzes and brasses Precious metals Welding, brazing and soldering alloys Various plating alloys

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Materials Properties cont..

? Fracture Toughness
– The fracture toughness is a measure of the damage tolerance of a material containing initial flaws or cracks. The fracture toughness in metallic materials is described by the plain strain value of the critical stress intensity factor. The fracture toughness depends on the environment. Kic is the plain strain critical stress intensity factor. Kiscc plain strain critical stress intensity factor for a specified environment in which environmentally induced crack growth occurs. ? For homogeneous materials the Kic or Kiscc shall be measured according to ECSS- Q- 7045. Metallic materials for use in corrosive surface environments shall be tested for fracture toughness under representative conditions

?

Typical subcritical crack propagation rate versus stress intensity relationship. Stress intensity K, is defined as K=A??(?C/B), where ? is the total tensile stress, C is the crack length, and A and B are geometrical constants

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Materials Properties cont..

? Coefficient of thermal expansion and coefficient of moisture expansion
– The difference in thermal or moisture expansion between members of a construction or between the constituents of a composite or a coated material can induce large stresses or strains and can eventually lead to failures. The thermal mismatch between members shall be minimised to such a degree that stresses generated in the experienced temperature domain are acceptable. The coefficient of thermal expansion (CTE) of composite materials intended for high stability structural applications shall systematically be determined by means of dry test coupons and dry test conditions.







For hygroscopic materials intended for high stability structural applications,the coefficient of moisture expansion (CME) shall systematically be determined.
For composite materials a sensitivity analysis shall be performed in relation with the inaccuracies due to the manufacturing process.



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Materials Properties cont..

? Mechanical contact surface effects
– When clean surfaces are placed in contact they do not touch over the whole of their apparent area. The load is supported by surface irregularities and the following interactions can occur: ? elastic or plastic deformation ? adhesion ? material transfer and removal ? heat transfer ? chemical reaction ? transformation of kinetic energy into heat energy ? diffusion/localised melting For very clean surfaces strong adhesion occurs at regions of real contact, a part of which may be due to cold-welding The friction behaviour of polymers differs from that of metals. The surfaces left in contact under load may creep and high local temperatures can be generated by frictional heating at regions of real contact. Wear is the progressive loss of material from the operating surface of a body occurring as a result of relative motion at the surface. Wear is usually detrimental, but in mild form may be beneficial, e.g., during the running-in of engineering surfaces. The major types of wear are abrasive wear, adhesive wear, erosive wear, rolling wear and fretting. Materials and Processes Division ESA/ESTEC/TOS-QM sheet7

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Materials Properties cont..

? Stress Corrosion Cracking
– Stress corrosion maybe defined as the combined action of sustained tensile stress and corrosion that may lead to the premature failure of materials. Certain materials are more susceptible than others. If a susceptible material is placed in a corrosive environment under tension of sufficient magnitude, and the duration of service is sufficient to permit the initiation and growth of cracks, failure will occur at a stress lower than that which the material would normally be expected to withstand. The corrosive environment need not be severe in terms of general corrosive attack. Service failures due to stress corrosion are frequently encountered in cases where the surfaces of the failed parts are not visibly corroded in a general sense. If failure is to be avoided, the total tensile strength in service must be maintained at a safe level. There is no absolute threshold stress for stress corrosion, but comparative stress-corrosion thresholds can be determined for materials subjected to controlled conditions of test. Estimates of the stress-corrosion threshold for a specific service application must be determined for each alloy and heat treatment, using a test piece, stressing procedure and corrosive environment that are appropriate for the intended service.

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Materials Properties cont..

? Stress corrosion




Stress Corrosion Cracking (SCC), defined as the combined action of a sustained tensile stress and corrosion, can cause the premature failure of metals. The metallic components proposed for use in most spacecrafts must be screened to prevent failures resulting from SCC. Only those products found to possess a high resistance to stress-corrosion cracking may have unrestricted usage in structural applications. Materials intended for structural applications and likely to be exposed to a long-term terrestrial storage or flown on the Space Transportation System, fracture critical items, all parts used or associated with the fabrication of launch vehicles shall possess a high resistance to stress-corrosion cracking. Structural products of a metallic nature shall be selected from the preferred list in Table I of ECSS- Q70- 36.





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Materials Properties cont..

Specimen orientation and fracture plane identification. L, length, longitudinal, principal direction of metal working (rolling, extrusion, axis of forging); T, width, long-transverse grain direction; S, thickness, short-transverse grain direction; C, chord of cylindrical cross section; R, radius of cylindrical cross section. First letter: normal to the fracture plane (loading direction); second letter: direction of crack propagation in fracture plane.

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Materials Properties cont..

? SCC table I
– Materials that testing and experience have shown to possess high resistance to stress- corrosion cracking. Their use is given reference.

? SCC table II
– Alloys and tempers listed in table II are moderately resistant to stress- corrosion cracking. They should be considered for use only in cases where a suitable alloy cannot be found in Table I.

? SCC table III
– Materials listed in table III have found to be highly susceptible to stress- corrosion cracking. They should be considered for use only in applications where it can be demonstrated conclusively that the probability of stress corrosion is remote because of low sustained tensile stress (whatever its origin) in critical grain directions, suitable protective measures or an innocuous environment.

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Constraints on materials

? ? ? ? ? ? ? ?

Temperature Vacuum Thermal cycling Chemical (corrosion) Galvanic compatibility Atomic oxygen Moisture absorption/desorption Fluid compatibility
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Constraints on materials, cont..

? Temperature
– The range of temperatures experienced will play a large part in the materials selection. Extremes are illustrated by the examples of cryogenic tanks and thermal protection systems for re-entry applications. Temperatures below room temperature generally cause an increase in strength properties, however the ductility decreases. Ductility and strength may increase or decrease at temperatures above room temperature. This change depends on many factors, such as temperature and time of exposure. Materials shall be compatible with the thermal environment to which they are exposed. Passage through transition temperatures (e.g., brittle-ductile transitions or glass transition temperatures including the effects of moisture or other phase transitions) shall be taken into account.

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Constraints on materials cont..

? Thermal cycling
– Thermal cycling can induce thermal stresses and due to the difference in coefficient of thermal expansion between fibres and matrix for composites and between base metal and coating microcracks can form which could jeopardise long-term properties. ? Materials subject to thermal cycling shall be assessed to ensure their capability to withstand the induced thermal stresses and shall be tested according to ECSS- Q- 70- 04.

? Chemical (corrosion)
– The chemical environment to which a material is subjected in its life span may cause changes in the material properties. Corrosion is the reaction of the engineering material with its environment with a consequent deterioration in properties of the material. Corrosion will include the reaction of metals, glasses, ionic solids, polymeric solids and composites with environments that embrace liquid metal, gases, non-aqueous electrolytes and other non-aqueous solutions, coating systems and adhesion systems.

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Constraints on materials cont..

? Galvanic compatibility
– If two or more dissimilar materials are in direct electrical contact in a corrosive solution or atmosphere galvanic corrosion might occur. The less resistant material becomes the anode and the more resistant the cathode. The cathodic material corrodes very little or not at all, while the corrosion of the anodic material is greatly enhanced. ? Material compatibilities shall be selected in accordance with ECSS- Q-70-71, ? Maximum potential differences shall be in accordance with ECSS- Q-70-71, In the construction of a satellite, two metals that form a compatible couple may have to be placed in close proximity to one another. Although this may not cause anomalies or malfunctions in the space environment, it has to be borne in mind that spacecraft often have to be stored on earth for considerable periods of time and that during storage they may inadvertently be exposed to environments where galvanic corrosion can take place. In fact, this is known to have taken place on several occasions and it is for this reason that the Agency has been studying the dangers involved.



? See also paragraph about Corrosion
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Constraints on materials cont..

? procedure
– a simplified procedure can be used to estimate the compatibility of a bimetallic couple by taking into account the difference between the two static potentials of the materials involved. The potentials were measured in a 3.5 % NaCl solution representing a standard corroding atmosphere



? ruling
– A difference in the static corrosion potential of the two metals forming a bimetallic couple of less than 0.5 V is acceptable if the item containing the couple is held in a clean-room atmosphere at all times. If the item containing the bimetallic couple is not held in a clean-room atmosphere, the allowable difference in static corrosion potential must be less than 0.25 V. If it is not possible to follow guidelines 1 and 2, then it will be necessary to provide for an insulation layer or special packaging.. Materials and Processes Division ESA/ESTEC/TOS-QM
Instrumentation setup for electrochemical experiments





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Constraints on materials cont..

? Atomic oxygen
– Spacecraft in low earth orbit (LEO) at altitudes of between 200 km and 700 km are exposed to a flux of atomic oxygen. The flux level varies with altitude, velocity vector and solar activity. The fluence levels vary with the duration of exposure.

? Moisture absorption/desorption
– The properties of composite materials are susceptible to changes induced by the take-up of moisture. Moisture absorption occurs during production of components and launch of the spacecraft, desorption occurs in the space vacuum.

? Fluid compatibility
– In some occasions materials are in contact with liquid oxygen, gaseous oxygen or other reactive fluids or could come into contact with such a fluid during an emergency situation.

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Interfaces (surfaces, layers)

? ? ? ? ? ? ? ? ?

Anodising Chemical conversion metallic coatings (overlay and diffusion) hard coatings Diffusion barriers High temperature oxidation protective coatings Thermal barriers Moisture barriers coatings on CFRP
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Surface finishes

? The surface finish of a component can influence its mechanical and environmental durability.
? Anodising (chromic, sulphuric, sulphuric+oxalic)
– – – Anodising is an electrolytic process for thickening and stabilising oxide films on base metals and anodising grade alloys. It may be used as a pre-treatment for painting and dying or as a passivation treatment for an electro-brightened surface. Hard anodised layers are wear resistant and durable. Black anodising with cobalt sulphide and nickel sulphide is used for controlling the optical properties of surfaces. ? High solar absorptance, high emmitnace The anodised layer is electrically non-conductive. The bath constituents and process conditions may vary between organisations. Caution should be exercised in anodising very thin products such as foils Coatings are porous and needs sealing (coating can release water in vacuum)

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Surface finishes, cont..

? Chemical conversion (chromate, phosphate) – –


– – – – –

Commercial process (alodine , irridite, etc) Chemical conversion depends upon the absorption of a protective metal oxide film into an existing oxide film but may include non-metals in some cases. Chromating involves the formation of a mixed metal-chromium oxide film. It has a good corrosion resistance and an excellent bond to subsequent organic coatings. Phosphating is primarily used as an underlayer for paint finishes. It finds little application for corrosion protection. Chemical conversion coatings can be either electrically conductive or non-conductive. Temporary corrosion protection only simple and cheap process may be applied by immersion, praying, brushing, wiping or any other wetting method

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Coatings, cont..
? Metallic coatings (overlay and diffusion)
– – – – – – Metallic overlay coatings can be applied in numerous ways to substrates (e.g. electroplating, chemical evaporation and ion sputtering). Metallic diffusion coatings modify the composition of the surface by enrichment with Cr, Al or Si and/or formation of their stable oxides. Cadmium and Zinc coatings shall not be used because of their high vapour pressure. Silver, copper and osmium coatings shall not be used on external surfaces because they are sensitive to atomic oxygen. Electroplated tin can form whiskers noble coatings such as gold and silver should be continuous (e.g. corrosion such as red plague)

? Hard coatings
– Hard coatings are used to improve the abrasive properties of the surface. Also, the ability to cold weld is greatly reduced. The combination of a hard coating and a soft substrate is not desirable. The coating can break under pressure.

? Diffusion barriers




High temperature service operation can result in compositional changes of the bulk material and of the coating due to diffusion. These compositional changes can result for example in formation of intermetallic compounds, which are brittle and can break under cyclic stresses. E.G. Cu or Ni layer as diffusion barrier between a brass (Cu-Zn) substrate and a Sn/Sn-Pb coating Materials and Processes Division ESA/ESTEC/TOS-QM sheet21

Coatings, cont.. evaporation

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Coating, cont.. Wear

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Coating, cont..

? Moisture barriers
– Coatings can be used to prevent moisture absorption or desorption of dimensionally stable structures or to prevent the release of organic volatiles which could affect the performances of some equipments.

? Coatings on CFRP
– Coatings on CFRP are used as moisture stoppers, as protection against atomic oxygen or for adjusting optical properties. In most cases these coatings are metallic. In this dissimilar material contact the CFRP usually behaves as the cathode and as such can corrodes the coating material.

? High Temp oxidation protective coatings (metallic)
– Protective coatings are important in high temperature applications, such as re-entry surfaces and propulsion systems. Oxidation protection, thermal shock behaviour and erosion properties are properties to consider.

? Thermal barriers (ceramic)
– Thermal barrier coatings are used to retard component overheating due to high heat fluxes. These coatings are essentially ceramic overlay coatings, based on zirconia, where the coating thickness is approximately 0.4 mm. They are applied to selected regions only. The coating process can modify the condition of the substrate. Materials and Processes Division ESA/ESTEC/TOS-QM sheet24

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Coating, cont..

? Depending on the design and service, the following coatings are used:
– – – – – – – – – – – – – – Paints phosphate coatings chromate coatings electroless nickel chromium, electroplated oxides and black oxide nickel/tin, electroplated tin/lead electroless nickel plus electroplated chromium vapour-deposited aluminium metals, such as gold, silver, palladium, rodium lubrication coatings such as braycoat grease molybdenum disulfide carbides and nitrides or combination

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Joining

? ? ? ?

Mechanical fastening Bonding Combined bonding and fastening Fusion, including welding, brazing, soldering and diffusion bonding

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Joining cont..

? Bolted joints
– – Bolts offer the greatest strength for mechanical fastened joints. Unless overtightened, no damage is done to the structure during assembly. Threaded fasteners shall conform to the minimum requirements of ECSS- E- 30- 07.

? Riveted joints
– Riveted joints are permanent. Disassembly requires removal of rivets by drilling out. Riveted joints shall not be used where access to internal or adjacent parts of the structure is either needed or expected.

? Inserts
– – An insert system consists of a removable threaded fastener and a fixture embedded into the honeycomb structure using a potting mass. All inserts shall be surface protected to avoid corrosion

? Adhesive bonding
– – The adhesives must attach the facings rigidly to the core to allow loads to be transmitted from one facing to the other. Guidelines for adhesive bonding are found in ECSS- E- 30- 05. Adhesives for load carrying structures shall have high strength and modulus. In addition, good toughness and peel strength are important. Materials and Processes Division ESA/ESTEC/TOS-QM sheet27

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Joining cont..

? Fusion techniques can be grouped as:
– – – soldering brazing welding, including diffusion bonding

? All fusion methods produce permanent joints. Soldered, and some brazed joints may be disassembled with care. ? All fusion techniques require extensive quality control and inspection procedures.
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Joining cont..

? Soldering
– – – Soldering is commonly referred to as soft soldering in which low melting point alloys such as Tin-Lead or Indium based alloys are used. Soldered joints are used for electrical and thermal conducting paths and for low mechanical strength joints. Soldering shall not be used for structural applications unless reviewed and approved by the Customer. See also next session

? Brazing
– Brazing is preferred to soldering in those cases where a strong joint, which is heat resistant is required. As distinct from soft soldering brazing usually refers to joining with alloys of copper, silver and zinc

? Welding
– Numerous welding techniques are available. In the aerospace industry the following techniques are often used: ? Tungsten Inert Gas (TIG) welding ? Plasma-Arc welding ? Electron Beam (EB) welding , laser welding ? Resistance welding (induction, spot, seam welding), Diffusion welding Materials and Processes Division ESA/ESTEC/TOS-QM sheet29

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Corrosion Testing

? ? ? ? ?

General Corrosion Stress Corrosion Bimetallic Corrosion Atomic Oxygen Corrosion Red Plague Corrosion

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Corrosion-General
? Four systems for corrosion testing are available, each covering a different area of corrosion evaluation
? ? ? ? ? ? ? Corrosion Units: humidity test chamber, testing according to ASTM salt spray test chamber, testing according to ASTM-B117 stress corrosion test rig, testing according to ASTM-G44 bimetallic corrosion set-up atomic oxygen corrosion red plague corrosion test unit, testing according to ESA PSS-01720
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General corrosion testing

Salt-spray-(foreground) and Humidity Chamber- both have temperature and humidity regulators
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Stress corrosion testing

Al-Li stress corrosion failure Testing acc. to ESA PSS-01-737 Test setup for the alternate immersion testing of specimens in a 3.5% NaCl solution
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Bimetallic corrosion testing

The bimetallic corrosion between two materials can tested in specific liquids and under any humidity levels. The current and voltage difference as well as the EMK’s vs Calomel as recorded

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Atomic Oxygen Corrosion
Materials for use in space applications in low earth orbit and exposed to the hostile combination of atomic oxygen and thermal cycling have to be screened for their susceptibility to withstand this environment over very long periods

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Red plague testing

Red plague testing (Anthony and Brown test) is performed according to ESA PSS01-720 Test conditions: 240 hrs at 58 oC
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Mechanical Testing

? ? ? ? ? ?

Hardness testing Tensile Testing Compression testing Fatigue testing Fracture Toughness Thermal cycling

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Mechanical Testing cont..
Load cells may be changed so that full scale chart readings of between 2N and 100kN (maximum capacity) can be achieved in both tension and compression. This equipment will investigate the mechanical properties of all materials at temperatures ranging from -150oC to +300oC

General view of Instron tensile test equipment with custom built environmental chamber, chart recorder and control panel

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Mechanical Testing cont..
This equipment is more particularly dedicated to the testing of thermostructural materials such as CMC materials. It has been set up for measuring tensile properties from ambient temperature up to 1600oC under air. Such a test is recognised to be the most important for evaluating mechanical properties of CMC.

A ceramic matrix composite specimen is clamped into self-aligning water cooled grips. It passes through a specially designed furnace able to heat its calibrated section to 1600oC. A high temperature capacitive extensometer made of ceramics probes permit strain measurements.
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Mechanical Testing cont..
Two units, specially designed according to to specification ESA PSS-01-704, operate under vacuum. Two other units operate under atmospheric pressure. The heating and cooling is provided by nitrogen gas.

One of the two systems for thermal cycling under vacuum (VMDI is shown). The system is provided with viewing ports and electric feed through connection.

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Macro/Microscopic Examination

? ? ? ?

Macroscopic (< X75) Light microscopy Confocal microscopy Scanning Electron Microscopy

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Macroscopic Examination

Magnification < x75
– – – – Visual Inspection Stereozoom Scanning Electron Microscopy at low magnification Photography

The diversity of samples submitted for failure analysis is illustrated by this photograph, which features part of a defective spacecraft antenna, a nickel cadmium battery cell, detector electrodes, printed circuit boards, fracture toughness specimen, part of a dip brazed waveguide, sections through a solar army hydrogen embrittled springs and a composite structure designed to withstand the impact of particles travelling at 60 km/s.
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Microscopic Examination cont..

? Light Microscopy
– metallurgical microscopy

?

Optical Microscopes Reichert MeF2: magn. X1 to X1500, It includes: interferometer, polarised light illumination, micro-hardness tester Reichert MeF3a: magn. X1 to 1500 It includes: polarised light illumination, dark and bright field illumination, connection to Clemex Image analyser

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Microscopic Examination cont..
Confocal microscopy
Confocal microscopy allows the us to obtain depth-selective information on the threedimensionial structure of a microscopic object.

LEICA TCS NT with microscope DM-RXE and galvanometer driven Z-stage. The x/y resolution is 0.18 ?m (FWHM) and a corresponding zresolution of better than 0.35 ?m (FWHM) at 488 nm

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Microscopic Examination cont..
? In many situations even greater magnifications are useful. This capability is provided by two Scanning Electron Microscopes (SEM) which can magnify to X200 000 with good resolution. (JEOL T300 and Cambridge S360). The great depth of field of these instruments and the large specimen chamber of one of these SEM's has made them particularly useful in examining rough fracture surfaces to determine the cause of a component failure.

?

View on Scanning Electron Microscope Cambridge S360

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Non-Destructive Examination

? Scanning Laser Acoustic Microscopy (SLAM) ? C- Mode Scanning Acoustic Microscopy (C-SAM) ? Radiography (in TOS-QC)

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Non-Destructive Examination cont..
The Scanning Laser Acoustic Microscopy (SLAM) produces images of the internal structure of metals, ceramics and even biological tissues, and these are displayed in real time on a TV monitor.

The SLAM uses very high frequency ultrasound in a transmission mode to produce images. Acoustic waves are transmitted into the bottom face of the cell sample by means of a distilled-water coupling medium. Using this instrument it was possible to assess the quality of solar cell interconnectors for the Space Telescope.
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Failure Analysis

? Under control of Material Review Board (MRB)
? ? ? ? ? ? ? ? ? ? Collection of background data visual examination selection, identification, preservation of specimens macroscopic examination and analysis microscopic examination and analysis metallographic sections examination failure mechanism chemical analysis simulated testing report
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Materials Properties annex cont.. ? Corrosion fatigue


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Corrosion fatigue indicates crack formation and propagation caused by the effect of alternating loading in the presence of a corrosion process. Because of the time dependence of corrosion, the number of cycles to failure depends on frequency. Since chemical attack requires time to take effect, its influence is greater as the frequency becomes lower. No metals or alloys demonstrate complete resistance to corrosion fatigue. ? Same requirement as with fatigue

? Hydrogen embrittlement
– Metals can be embrittled by absorbed hydrogen to such a degree that the application of the smallest tensile stress can cause the formation of cracking. The following are possible sources of hydrogen: thermal dissociation of water in metallurgical processes (e.g., casting and welding), decomposition of gases, pickling, corrosion, galvanic processes (e. g. plating) and ion bombardment. ? The possibility of hydrogen embrittlement during component manufacture and/or use shall be assessed

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Materials Properties annex cont.. ? Strength


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Spacecraft design covers the survival of the structure under the worst feasible combination of mechanical and thermal loads. All events of the complete lifetime of the spacecraft are addressed by this design. The strength of a material is highly dependant on the direction as well as on the sign of the applied load, e.g., axial tensile, transverse compressive, and others. ? positive margin of safety and shall include, if applicable, yield load analysis, ultimate load analysis and bucking load analysis

? Elastic modulus
– The elastic modulus defined as the ratio between the uniaxial stress and the strain (e.g., Young’s modulus, compressive modulus, shear modulus) is for metals and alloys weakly dependant on heattreatment and orientation. However, for fibre reinforced materials, the elastic modulus depends on the fibre orientation. ? For composites the required elastic modulus shall be verified.

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Materials Properties annex cont.. ? Fatigue


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Fatigue fracture can form in components which are subjected to alternating stresses. These stresses may lie far below the allowed static strength of the material. ? For components experiencing alternating stresses, demonstration of the degradation of material properties over the complete mission

? Fracture toughness
– The fracture toughness is a measure of the damage tolerance of a material containing initial flaws or cracks. The fracture toughness in metallic materials is described by the plain strain value of the critical stress intensity factor. The fracture toughness depends on the environment. Kic is the plain strain critical stress intensity factor. Kiscc plain strain critical stress intensity factor for a specified environment in which environmentally induced crack growth occurs. ? Metallic materials for use in corrosive surface environments shall be tested for fracture toughness under representative conditions

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Materials Properties annex cont.. ? Creep


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Creep is a time-dependant deformation of a material under an applied load. It usually occurs at elevated temperature, although some materials creep at room temperature. If permitted to continue indefinitely, creep terminates in rupture. Extrapolations from simple to complex stress-temperaturetime conditions are difficult. ? Testing under representative service conditions is necessary when creep is likely to occur.

? Micro-yielding
– Some materials may exhibit residual strain after mechanical loading. The micro-yield is the force to be applied to get a residual strain of 1x10-6 m/m along the tensile or compression loading direction. In general, the most severe mechanical loading occurs during launch. ? Where dimensional stability requirements have to be met, micro-yielding shall be assessed. ? When it is likely to occur, testing and analysis in relation with the mechanical loading during the life cycle of the hardware shall be performed.

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Stress Corrosion Cracking, cont..

The relative influences of electrochemical and mechanical factors in the corrosion and SCC damage of a susceptible material. The shaded area represents the transition of driving force from dominance by electrochemical factors to chiefly mechanical factors. Precise separation of initiation and propagation stages is experimentally difficult. Stimulation of cracking by atomic hydrogen may also become involved in this transition region.

Effect of stress intensity on the kinetics of SCC. Stages I and II may not always be straight lines but may be strongly,curved, and one or the other may be absent in some systems. Stage III is of little interest and is generally absent in K-decreasing tests.

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Stress Corrosion Cracking, cont

Mean breaking stress versus exposure time for short-transverse 3.2-mm (0. 1 25-in.) diam aluminium alloy 7075 tension specimens tested according to ASTM G 44 at various exposure stress levels. Each point represents an average of five specimens.

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Stress Corrosion Cracking, cont..

Effect of temper on SCC performance of aluminum alloy 7075 subjected to alternate immersion in 3.5% NaCl solution at a stress of 207 MPa (30 ksi). Mean flaw depth was calculated from the average breaking strength of five specimens subjected to identical conditions. Source: Ref 17

Influence of specimen configuration on SCC test performance (alternate immersion in 3.5% sodium chloride per ASTM G 44). Aiuminum alloy 7075-T7X51 specimens stressed 310 MPa (45 ksi); each point represents 60 to 90 specimens. Source: Ref 18

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SCC Table I - Steel Alloys

Alloy Carbon steel(1000 series) Low alloy steel(4130,4340 etc) (E) D6AC, H-11 Music wire(ASTM 228) HY-80 steel HY-130 steel HY-140 steel 1095 spring steel 300 series stainless steel(unsensitised)2 400 series ferritic stainless steel 21-6-9 stainless steel Carpenter 20 Cb Stainless steel Carpenter 200 Cb-3 stainless steel A286 stainless steel AM350 stainless steel AM355 stainless steel Almar 362 stainless steel Custom 450 stainless steel Custom 455 stainless steel 15-5 PH stainless steel PH 14-8 Mo stainless steel PH 15-7 Mo stainless steel 17-7 PH stainless steel Nitronic 33 (3) (E) Maraging steel MARVAL X12

Condition Below 125 kg/mm2; (180 ksi) UTS Below 125 kg/mm2; (180 ksi) UTS (1) Below 148 kg/mm2; (210 ksi) UTS cold drawn Quenched and tempered Quenched and tempered Quenched and tempered Quenched and tempered All All All All All All SCT 1000(4) and above SCT 1000 and above H1000 (5) and above H1000 and above H1000 and above H1000 and above CH900 and SRH950 and above (6,7) CH900 CH900 All All

1) A small number of laboratory failures of specimens cut from plate more than 2 inches thick have been observed at 75% yield, even within this ultimate strength range. The use of thick plate should therefore be avoided in a corrosive environment when sustained tensile stress in the short transverse direction is expected. 2) Including weldments of 304L, 316L, 321 and 347. 3) Including weldments. 4) SCT 1000 = sub-zero cooling and tempering at 538&#176;C (1000F) 5) H1000 = hardened above 538C (1000F) 6) CH900 = cold worked and aged at 480C (1000;F) 7) SRH950 = solution treated and tempered at 510C (950F) (E) ESA classification - not in NASA MSFC-SPEC-522A

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SCC Table I - Nickel Alloys

Alloy Hastelloy C Hastelloy X Incoloy 800 Incoloy 901 Incoloy 903 Inconel 600 (3) Inconel 625 Inconel 718 (3) Inconel X-750 Monel K-500 NiSpan -C 902 Rene 41 Unitemp 212 Waspaloy 3) Including weldments

Condition All All All All All Annealed Annealed All All All All All All All

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SCC Table I - Aluminium Alloys

All 355.0, C355.0 T6 356.0, A356.0 All T8 357.0 All T8 B358.0 (Tens-50) All T6, T8 359.0 All T8 380.0, A380.0 As cast T6, T8 514.0 (214) As cast (5) 518.0 (218) As cast (5) All 535.0 (Almag 35) As cast (5) All (4,5) A 712.0, C 712.0 As cast All T6 (6) T73 T73 T73 T73 T73 1) Mechanical stress relieved (TX5X or TX5XX) where possible 2) Including weldments of the weldable alloys. 3) The former designation in shown in parenthesis when significantly different. 4) High magnesium content alloys 5456, 5083 and 5086 should be used only in controlled tempers (H111, H112, H116, H117, H323, H343) for resistance to stress-corrosion cracking and exfoliation 5) Alloys with magnesium content greater than 3.0% are not recommended for high temperature application, 66C (150F) and above. 6) Excluding weldments. (E) ESA classification - not in NASA MSFC-SPEC-522A

Alloy, Wrought(1,2) Alloy, 1000 series 2011 2024, rod bar 2219 (E) 2419 (E) 2618 3000 series 5000 series 6000 series (E)7020 7049 7149 7050 7075 7475

Condition

Cast (3)

Condition

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SME Initiative
SCC Table I - Copper Alloys/ Misc. Alloys

CDA no (1) 110 170 172 194 195 230 422 443 510 521 619 619 688 706 725 280,524,606 632,655,705 710,715 (E)917, (E)937

Condition (% cold rolled) (2) 37 AT, HT (3) AT, HT (3) 37 90 40 37 10 37 37 40(9% B phase) 40(95% B phase) 40 50 50, annealed 0 0 0 0

Alloy Beryllium, S-200C HS 25 (L605) HS 188 MP35N Titanium 3Al-2.5V Titanium 6Al-4V Titanium 13V-11Cr-3Al (E)Titanium OMI 685, IMI 829 Magnesium, M1A Magnesium, LA141 Magnesium, LAZ933

Condition Annealed All All All All All All All All Stabilised All

1) Copper Development Association alloy number 2) Maximum per cent cold rolled for which stress-corrosion cracking data are available 3) AT = annealed and precepitation hardened, HT = work hardened and precepitation hardened

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SCC Table II - Steel Alloys/Miscellaneous alloys

SME Initiative

Alloy Carbon steel (1000 series) Low-alloy steel (4130,4340 etc) Nitronic 32 Nitronic 60 400 series martensitic stainless steel (except 440) PH 13-8 Mo stainless steel 15-5 PH stainless steel 17-4 PH stainless steel

Condition 1225 to 1370 MPa UTS 1225 to 1370 MPa UTS All All (1) All Below H1000 (2) All

1) Tempering between 370 and 600C should be avoided because corrosion and stress-corrosion resistance is lowered. 2) H1000 = hardened above 538C (1000F).

Alloy Magnesium AZ31B Magnesium ZK60A Magnesium (E) ZW3

Condition All All All

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SCC Table II - Aluminium Alloys(1,2)
Alloy, wrough 2024 rod, bar, extrusion 2024 plate, extrusions 2124 plate 2048 plate 4032 5083 5086 5456 7001 (E) 7010 7049 7050 7075 7175 7475 7178 (E) Russian Al-Li 1420, 1421 Alloy, cast 319.0, A319.0 333.0, A333.0 Condition As cast As cast

Condition T6, T62 T8 T8 T8 T6 All (3) All (3) All (3) T75, T76 T74 T76 T74, T76 T76 T74, T76 T76 T76 soln. treat+age

1) Mechanically stress relieved products (TX5X or TX5XX) should be specified where possible. 2) Sheet, unmachined extrusion and unmachined plate are the most resistant forms. 3) Except for controlled tempers listed in footnote 3 of Table I, aluminium alloys. These alloys are not recommended for high-temperature applications. 66C (150F) and above. (E) ESA classification - not in NASA MSFC-SPEC-522A.

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SCC Table III - Steel Alloys
Alloy Carbon steel(1000 series) Low alloy steel(4130,4340 etc) (E) D6AC, H-11steel 440C stainless steel 18 Ni Maraging steel, 200 grade 18 Ni Maraging steel, 250 grade 18 Ni Maraging steel, 300 grade 18 Ni Maraging steel, 350 grade AM 350 stainless steel AM 355 stainless steel Custom 455 stainless steel PH 15-7 Mo stainless steel 17-7 PH stainless steel CH900 (E) Kovar Condition Above 1370 Mpa UTS Above 1370 Mpa UTS Above 1370 Mpa UTS All Aged at 900F Aged at 900F Aged at 900F Aged at 900F Below SCT 1000 Below SCT 1000 Below H1000 All except CH900 All except CH900 All

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SCC Table III - Aluminium Alloys
Alloy, Wrought (1,2) 2011 2014 2017 2024 2024 Forgings 2024 Plate (E) Al-Li 2080 (E) 2618 7001 7005 (E) 7020 7039 7075 7175 7079 7178 7475 (E) Al-Li 8090 (E) BS L93 (E) Russian Al-Li 1441, 1460 Condition T3, T4 All All T3, T4 T6, T62, T8 T62 T8 T3, T4 T6 All Weldments All T6 T6 T6 T6 T6 All T6 All Alloy 295.0 (195) B295.0 (B195) 520.0 (220) 707.0 (607, tern-alloy 7) D712.0 (D612, 40E) Condition T6 T6 T4 T6 As cast

1) Mechanical stress relieved (TX5X or TX5XX) should be specified where possible.<br> 2) Sheet, unmachined extrusion and unmachined plate are the least susceptible forms.<br> (E) ESA classification - not in NASA MSFC-SPEC-522A.

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SCC Table III - Copper Alloys/ Magnesium alloys
CDA no (1) 260 353 443 672 687 762 766 770 782 Condition (% cold rolled) (2) 50 50 40 50, annealed 10, 40 A, 25, 50 38 38, 50, annealed 50 Alloy Magnesium AZ61B Magnesium AZ80A Magnesium WE54 Magnesium ZCM711 Condition All All All All

1) Copper Development Association alloy number 2) Rating based on listed conditions only

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