Showing papers on "Fractography published in 1989"
TL;DR: Fracture toughness and tension tests were performed on two aluminum alloy matrices, 2014-O and 2024-O reinforced with alumina particulates of different volume fractions and particulate sizes.
237 citations
TL;DR: It is demonstrated that quantitative fractography can be used to study failed aluminous and glass-ceramic central porcelains and calculate the in vivo stress at failure in a clinically fractured DICOR molar crown.
Abstract: This study demonstrated that quantitative fractography can be used to study failed aluminous and glass-ceramic central porcelains. Fracture surfaces of DICOR and Vitadur-N core porcelain modulous-of-rupture bars were studied to identify fracture mirror features useful in (1) locating the source of fracture and (2) calculating the stress at fracture in clinically failed restorations. The morphology of fracture surfaces results from events related to the initiation and propagation of the crack front during failure. Modulus-of-rupture testing was performed in four-point bending. Fracture surfaces were studied by scanning electron microscopy. The mean fracture stress for the Vitadur-N porcelain was 94.7 +/- 12.4 MPa (13,730 psi); for DICOR the fracture stress was 55.4 +/- 10.6 MPa (8,030 psi). The standard quantitative fractography relationship between in mirror radius and ln fracture stress was followed for both materials. This quantitative fractography relationship was used to calculate the in vivo stress at failure in a clinically fractured DICOR molar crown. Five clinically failed DICOR crowns were seen to fail from the internal surface.
222 citations
TL;DR: In this paper, fracture surface profiles were measured and related to fractal dimension using the techniques of quantitative metallography, but fracture toughness did not correlate with any measure of fracture surface roughness.
Abstract: Fracture toughnesses of several composites of aluminium alloys reinforced with particulate SiC have been measured. The variables were particulate size and volume fraction, and matrix alloy composition and heat treatment. Fracture surface profiles were measured and related to fractal dimension using the techniques of quantitative metallography. The fracture surface roughness was described well by fractals, but fracture toughness did not correlate with any measure of fracture surface roughness. An explanation for this behaviour is offered.
80 citations
TL;DR: In this paper, the reinforcement of hydroxy-apatite ceramics with metal fibres is discussed, and the results obtained are also promising for other metal fibre-ceramic matrix composites.
Abstract: The reinforcement of hydroxy-apatite ceramics with metal fibres is discussed. Hastelloy X and FeCralloy fibres were dispersed in hydroxy-apatite powder slurry. The fibre-powder slurries were dried and sieved over a wide aperture sieve. The resulting granules were used for die pressing. Volume fractions used were 10, 20 and 30%. The compacts obtained in this way were isostatically repressed at 4 k bar. These compacts showed considerable strength and toughness. Hot-pressing of the compacts was done at about 1000'C and a pressure between 0.2 and 1.0 k bar for 15 min. The resulting materials were characterized by fractography and strength, fracture toughness, Young's modulus and hardness measurements. Both strength and fracture toughness increased while Young's modulus and hardness decreased with increasing volume fraction of fibres. The strength and fracture toughness of composites containing 20 vol % metal fibres showed an increase of the strength and fracture toughness by a factor of about 2 and 6, respectively, as compared with the strength of about 100 M Pa and a toughness of 1 .0 MPa m1/2 for the sintered, pure matrix materials. The results obtained are also promising for other metal fibre-ceramic matrix composites.
80 citations
TL;DR: In this article, the microstructure/mechanical properties relationship in a mollusk shell, the large conch, Strombus gigas, have been investigated, showing that this material is very resistant to cracking; the damage zones around the indents strongly reflect the lamellar character of the shell.
Abstract: Preliminary investigations of the microstructure/mechanical properties relationship in a mollusk shell—the large conch, Strombus gigas—are reported. Strombus gigas has the well-ordered “crossed lamellar” microstructure and, in four-point bending, is remarkably tough in certain orientations, permitting noncatastrophic (“graceful”) failure. Fractography indicates that several toughening mechanisms are acting in concert, including crack bridging, microcracking, fiber pullout, and microstructurally induced crack arrest branching. Microindentation studies show that this material is very resistant to cracking; the damage zones around the indents strongly reflect the lamellar character of the microstructure.
77 citations
TL;DR: In this paper, rotating bending fatigue tests were conducted in laboratory air and dry air using smoothened specimens with 8 mm diameter, and no fatigue limits were observed in the long life range up to 109 cycles (10 months).
Abstract: In order to clarify the fatigue strength charactaristics of low alloy steels which were strengthed by tempering at low temperature (150∼200°C) after conventional quenching treatment and/or carburizing in generated gas, rotating bending fatigue tests were conducted in laboratory air and dry air using smoothened specimens with 8 mm diameter. The influence of moisture in air was only recognized for the carburized steel. The S-N diagrams of both steels revealed two knees on those curves regardless of the test enviroments and no fatigue limits were observed in the long life range up to 109 cycles (10 months). The reasons were discovered from the results of fractography and the equation proposed by Murakami et al. for the prediction of fatigue limit of steel with micro defects.
56 citations
TL;DR: In this paper, the effects of matrix aging condition (i.e., matrix temper) on the fracture toughness of 2XXX and 7XXX Al matrix alloys reinforced with SiC particulates, and the results are compared with the mechanical behavior.
48 citations
TL;DR: In this article, stitching yarns were used to improve delamination resistance in composite laminates by using thermoplastic matrix resins and stitching yarn yarns, which showed a 20 to 30% increase in critical crack-opening load, a 20 times higher fatigue threshold, and a two-orders-of-magnitude increase in fatigue life.
Abstract: This paper shows how to improve delamination resistance in composite laminates by the use of thermoplastic matrix resins and by stitching Discussed are fatigue crack growth characteristics in thermoplastic matrix composites as well as the differences between the crack growth processes in thermoplastic and thermosetting matrix composites under cyclic fatigue and monotonically increasing loads Further improvement of delamination resistance achieved by stitching shows a 20 to 30% increase in the critical crack-opening load, a 20 times higher fatigue threshold, and a two-orders-of-magnitude increase in fatigue life Fractography evidence is presented to illustrate the role of the stitching yarns in resisting delamination A fracture model was constructed to simulate delamination crack propagation in the presence of stitching yarns The effects of geometric stitching parameters, as well as intrinsic and extrinsic yarn properties, were simulated with this fracture model Finally, practical issues on the effective and economical application of stitching to composite structures are discussed
46 citations
TL;DR: In this article, both dendritic structure and equiaxed grain structure are produced in cast Co-Cr-Mo alloy by controlling the cooling rate of castings during the solidification process, to determine whether a significant improvement in the mechanical properties of the alloy can be obtained.
Abstract: Both dendritic structure and equiaxed grain structure are produced in cast Co-Cr-Mo alloy by control of the cooling rate of castings during the solidification process, to determine whether a significant improvement in the mechanical properties of the alloy can be obtained. The different structural characteristics of the two kinds of casting are examined by optical microscopy, scanning electron microscopy and transmission electron microscopy. Tensile and fatigue tests as well as hardness measurement are carried out using individually cast test-pieces. Fracture surface appearance characteristics of tensile and fatigue specimens are also studied. It is concluded that the mechanical properties, including both transient and permanent properties, of the equiaxed grain structure castings obtained by fast cooling are superior to those found in the coarse dendritic structure castings.
43 citations
TL;DR: In this article, the fracture toughness of bainitic ductile iron transformed at various austempering temperatures and times was evaluated by using compact tension specimens and compared with the fracture strength of bulleye casting structure.
Abstract: — The fracture toughness of bainitic ductile iron transformed at various austempering temperatures and austempering times was evaluated by using compact tension specimens and compared with the fracture toughness of bulleye casting structure. Using Scanning Electron Microscopy, the mechanism of the fracture mode can be understood by observing the fracture surface. An X-ray diffractometer was used to determine the volume fraction of retained austenite. From the results of fracture toughness properties, it can be concluded that the most suitable austempering temperature of the material used in the present study is from 300 to 350°C.
TL;DR: In this paper, the development of dissipative mechanisms during the fracture of toughened polyamides is investigated by SEM, which is made possible by means of a simple technique for the cryogenic dissection of ductile fracture surfaces.
Abstract: The development of dissipative mechanisms during the fracture of toughened polyamides is investigated by SEM. A preliminary fractographic analysis is carried out on the ductile fracture surfaces of water conditioned PA 6 specimens. Extensive yielding gives rise to a wide development of shear bands and rumples, depending on the local stress conditions. Then, the stress whitened regions under the ductile fracture surfaces of rubber toughened HI-PA 6 specimens are analysed by SEM. This is made possible by means of a simple technique for the cryogenic dissection of ductile fracture surfaces: sections are cut both transversally and longitudinally with respect to the ductile crack growth direction. Under the ductile fracture surfaces extensive cavitation occurs around the rubbery particles, following preferential and definite shear directions. The presence of cavitation is correlated with the distance below the ductile surfaces. The rumpled morphologies can be directly correlated with cavitation and shear bands occurring inside the whitened regions below ductile fractures. Both the orientation of shear bands on the fracture surfaces of water conditioned PA6 and the cavitation-shear yielding morphologies developed inside the fractured PA-rubber blends comply with an octahedral shear model, common to other polymers (rubber toughened epoxies, for instance) and to ductile metals.
TL;DR: In this article, the fatigue crack response in the accelerated crack propagation range can adequately be described by the Paris equation and the onset of stable crack propagation acceleration occurred above a characteristics threshold stress intensity factor (ΔKt) which separates the accelerated from that of the delayed stable crack growth region.
TL;DR: In this paper, the authors examined the constant amplitude fatigue crack growth behavior of a conventionally (α + β ) solution treated and aged Ti-6Al-4V fan disc forging by fractographic and microstructural analysis.
TL;DR: In this article, the influence of high purity hydrogen gas on the ductility of a normalized steel 15 MnNi 6 3 and of a thermomechanically treated steel X 56 TM was investigated at room temperature by tensile tests with constant extension rate for smooth specimens.
TL;DR: In this paper, the crack propagation characteristics of specimens of a unidirectionally reinforced α-Al2O3/Mg alloy metal matrix composite were investigated by means of fatigue crack propagation tests, tensile tests and fracture toughness tests.
Abstract: The crack propagation characteristics of specimens of a unidirectionally reinforced α-Al2O3/Mg alloy metal matrix composite were investigated by means of fatigue crack propagation tests, tensile tests and fracture toughness tests. Samples were tested in longitudinal and transverse orientations. Fatigue crack propagation rates were successfully measured for each orientation. Crack propagation modes were found to be dependent upon the applied stress intensity and the fibre orientation. The crack propagation rates can vary by several orders of magnitude between nominally identical samples. In thermal cycling tests, voids were nucleated at the fibre/matrix interface: these voids decreased the load-carrying capability of the metal matrix composite but increased the work of fracture in the longitudinal orientation.
TL;DR: In this paper, the morphology of fracture surfaces of unidirectional carbon fiber reinforced plastic composites has been studied to categorize the fractographic characteristics for several types of loading.
Abstract: The morphology of fracture surfaces of unidirectional carbon fibre reinforced plastic composites has been studied to categorize the fractographic characteristics for several types of loading. Specimens were tested in compression and in tension, both in the axial and the transverse direction, in bending and in interlaminar shear. The influence of prior exposure to moisture and to elevated temperature on the fracture morphology of specimens tested at elevated temperature has also been studied. Optical and scanning electron microscopy were used for the fracture surface analyses. Fractographic features characteristic of each mode of stressing and directionality of specimen were identified.
TL;DR: In this paper, a crack rail shear (CRS) specimen is used to characterize the interlaminar Mode III critical strain energy release rate (GIIIc) of continuous fiber-reinforced composite materials.
Abstract: The Crack Rail Shear (CRS) specimen is a proposed test method to characterize the interlaminar Mode III critical strain energy release rate (GIIIc) of continuous fiber-reinforced composite materials. The specimen utilizes the two rail shear test fixture and contains embedded Kapton film between designated plies to provide a starter crack for subsequent fracture testing. Analytical expressions for specimen compliance and GIII are based upon Strength of Materials (SM) principles. The model identifies important material and geometric parameters and provides a simple data reduction scheme. A quasi-three-dimensional, linear elastic finite element stress analysis verifies the purity of the Mode III fracture state and identifies admissible crack lengths to be used in the experimental study. A fully three-dimensional linear elastic finite element analysis of the CRS is employed to investigate the influence of edge effects on the fracture state for the finite length sample. Results based upon a uniform crack extension indicate a small region of mixed mode behavior at traction free edges which decay to a pure Model III fracture state in the interior of the sample. Furthermore, the GIII distribution along the crack front decreases at the free edges from a maximum plateau region in the interior. The three-dimensional analysis allows edge effects to be minimized by selecting appropriate specimen lengths. Compliance and strain energy release rates are in good agreement with the SM model. An experimental program was performed to measure GIIIc of two graphite epoxy systems. GIIIc results for AS4/3501-6 were found to be 1.6 times the Mode II fracture toughness, while IM7/8551-7 exhibited equivalent Mode II and Mode III fracture toughnesses. Mode III fracture surfaces revealed microstructural deformations characteristic of Mode II fracture.
01 Nov 1989-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the fractography of TSCC of 316 s.s. was studied, with particular attention paid to the crystallography of cracking and to the influence of the stress intensity factor K.
Abstract: The fractography of transgranular stress corrosion cracking (TSCC) of annealed 316 stainless steel (s.s.) tested in boiling MgCl2 solution at 154°C was studied, with particular attention paid to the crystallography of cracking and to the influence of the stress intensity factor K. Etch-pitting and stereographic observations were employed in order to determine the cracking crystallography. At low K values, cracking occurred predominantly on {100} planes with preferential propagation in a 〈110〉 direction. This crystallography and the fractographic features observed are consistent with the crack path alternating microscopically between two sets of {111} planes. Regions of {100}〈100〉 crack propagation were also observed and were consistent with cracking occurring microscopically on four sets of {111} planes. This latter cracking crystallography was often associated with herringbone and fan-shaped patterns of river lines. The latter patterns occurred especially at intermediate K values and were related to the relative ease of crack propagation within grains and across grain boundaries. At high K values, feather-like and sheet-like microfractographic features were generally observed and were shown to result from quite large decohesion steps on different sets of {111} planes. The variation in fractographic details with K was consistent with the number of {111} planes on which cracking occurred and with the size of the decohesion steps on the individual planes. The observations also indicated that the microscopic crack path followed planes which localized slip had occurred; however, these observations did not permit complete identification of the crack propagation mechanism. The strong similarity between the fractography of TSCC of 316 s.s. and of near-threshold fatigue cracking is discussed, as is the role of the fracture of river lines in influencing the fractographic features.
TL;DR: In this paper, the authors used the technique of scanning electron fractography to evaluate the extents of disordering and amorphization induced by proton irradiation in the intermetallic compounds NiTi, NiTi/sub 2, CuZr and Zr/sub 3/Al.
Abstract: The intermetallic compounds NiTi, NiTi/sub 2/, CuZr, CuTi/sub 2/, and Zr/sub 3/Al were irradiated by 2 MeV protons at various temperatures between --175 /degree/C and --44 /degree/C to a fluence of 1.9/times/10/sup 22/ H/sup +//m/sup 2/. Transmission electron microscopy, electron diffraction, and x-ray diffraction were used to evaluate the extents of disordering and amorphization induced by irradiation in the samples. Both phenomena progressed to varying extents in the five compounds, depending on the irradiation temperature and dose. It was observed that the C-A transition began before the degree of long-range order was reduced significantly, and that the amorphous phase nucleated homogeneously throughout the crystalline matrix. A major finding of the current investigation is that the technique of scanning electron fractography provides a useful correlation between the features of the fractured surfaces and the microstructural alterations induced by the proton irradiations. When amorphization is complete the fracture surfaces are either featureless (e.g., NiTi/sub 2/) or contain branching features resembling river patterns. In some cases (especially in CuZr) these are similar to the markings seen on the surface of fractured amorphous ribbons produced by melt-spinning. In general, however, there is not a particularly good correlation between the features on the fracture surfacesmore » of the irradiated and melt-spun ribbons. When the microstructure consists of amorphous regions embedded in a partially disordered crystalline matrix, there is consierable evidence for irradiation-induced ductility. In such cases, exemplified by the results on NiTi and Zr/sub 3/Al, the fracture surfaces contain dimples, characteristic of ductile fracture, suggesting that disordering promotes ductility.« less
TL;DR: In this article, fractographic evidence of slow crack growth in liquid Al was found, supporting a proposed explanation of the R-curve behavior which involves grain bridging across the crack.
Abstract: Microstructural defects identified in a TiB2–AIN composite were poorly bonded agglomerates, foreign inclusions, and highly strained regions There were also surface flaws Fracture surfaces produced in air were highly irregular, suggesting that microcracking caused the composite to behave differently from classical brittle ceramics Fracture at elevated temperature in Ar or in liquid Al produced the only crack branching observed No fractographic evidence of slow crack growth in liquid Al was found Fractographic observations support a proposed explanation of the R-curve behavior which involves grain bridging across the crack
TL;DR: In this paper, a fabrication technique for producing flexible superconductor wire by extrusion of a composite of Ag2O•YBa2 Cu3 O7−x is reported.
Abstract: A fabrication technique for producing flexible superconductor wire by extrusion of a composite of Ag2O‐YBa2 Cu3 O7−x is reported. During the course of processing, the superconductive transition of the starting powder is maintained, thus obviating the need for subsequent heat treatment. This nonpoisoning behavior of Ag2 O is of significant technical importance. Scanning electron fractography reveals a mixed mode fracture behavior of the material and the evidence of ductility. Magnetic measurements on the extruded wires show an onset temperature of 91 K. Resistivity measurements indicate that the electrical resistance of the as‐extruded wire essentially vanishes at liquid‐nitrogen temperature.
TL;DR: In this paper, the authors deal with the non-destructive evaluation of the topology of contact and with the use of this information to predict the effects that loads borne by these contacts have on mechanical properties.
Abstract: Contact between surfaces usually occurs at asperities under compression or at connecting ligaments, depending on how the interface is formed. This paper deals with the nondestructive evaluation of the topology of contact and with the use of this information to predict the effects that loads borne by these contacts have on mechanical properties. Two specific examples are discussed: a fatigue crack and a diffusion bond. Asperity contact along the fracture surface of a fatigue crack partially shields the crack tip from the externally applied driving force. Using information from acoustic experiments, the geometry of the asperities, the contacting stress, and the shielding stress intensity factor have been estimated. Acoustically, a diffusion bonded interface looks very similar to that joining the two sides of a partially closed crack. In this particular case, the acoustically determined geometry of well-bonded ligaments can be verified by fractography of destructively tested samples whose bond strength has also been determined. Models to determine the bond strength from the ligament geometry are being suggested.
TL;DR: In this article, fracture toughness of polycrystalline alumina and ceria partially-stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression.
Abstract: Fracture toughness of polycrystalline alumina and ceria partially-stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression. Stress states ranging from pure mode I, combined mode I and mode II, and pure mode II were obtained by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed-mode fracture toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda-lime glass and fracture surface observations showed that crack surface resistance arising from grain interlocking and abrasion was the main source of the increased fracture toughness in mode II loading of the polycrystalline ceramics. The normalized fracture toughness for pure mode II loading, (KII/KIc), increased with increasing grain size for the CeO2-TZP ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.
TL;DR: In this paper, the authors have studied the fatigue corrosion life of Zircaloy 4 in the iodine environment on smooth tensile specimens and found that the initiation step consists of only intergranular corrosion governed by the chemistry of the environment.
TL;DR: The fracture behavior of a bis-GMA resin was studied by means of the double-torsion test and the evidence supported the concept that the behavior of the crack during propagation was controlled by the amount of plastic deformation occurring at the crack tip.
Abstract: The fracture behavior of a bis-GMA resin was studied by means of the double-torsion test. The fracture parameter measured was the stress-intensity factor. Fracture occurred in either a stick-slip (unstable) or continuous (stable) manner, depending upon the test conditions. When stick-slip propagation occurred, the fracture surfaces showed characteristic crack-arrest lines. The fracture surfaces were examined by use of a reflected-light optical microscope. The stress-intensity factor for crack initiation was found to be related to the size of the crack-arrest line which, in turn, could be related to the Dugdale model for plastic zone size. The evidence supported the concept that the behavior of the crack during propagation was controlled by the amount of plastic deformation occurring at the crack tip.
01 Jun 1989-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the micromechanisms of dynamic crack growth at room temperature and a low temperature (−100°C) in an AISI 4340 steel studied by Ravichandran and Clifton were investigated.
Abstract: The present work is aimed at understanding the micromechanisms of dynamic crack growth at room temperature and a low temperature (−100°C) in an AISI 4340 steel studied by Ravichandran and Clifton. For this purpose, a fractographic and metallographic examination of the specimens used by Ravichandran and Clifton was carried out. Results showed that the steel contained an appreciable amount of upper bainite (about 15%). The study suggests that dynamic crack propagation in the 4340 steel occurs in two stages, i.e. nucleation of microcracks in the upper bainite followed by propagation of these microcracks into the surrounding martensite. At low temperatures, failure of the martensite occurs by cleavage whereas, at room temperature, it occurs by shear localization, leading to microvoid growth and coalescence. At both temperatures, bainitic microcracks serve as failure initiation sites and reduce the dynamic fracture toughness of the steel.
TL;DR: In this article, the effects of glass content, fiber length, fiber orientation, and surface treatment on the fatigue fracture surface of reaction injection molded (RIM) nylon 6 were investigated.
Abstract: This study was undertaken to determine how milled glass fibers affect the fatigue resistance of reaction injection molded (RIM) nylon 6. Specifically the effects of glass content, fiber length, orientation, and surface treatment were investigated. The fatigue crack growth rates for unfilled and glass-filled samples were observed to follow the well-known Paris equation in terms of dependence on cyclic stress intensity factor. For the unfilled nylon a line shaped zone was observed in advance of the crack tip. Fractography results suggest that the zone was the projection of the actual crack tip profile through the thickness of the sample rather than a distinct plastic or deformation zone. The fatigue fracture surface exhibited a patchy type structure with features 50–150 μm in size, suggesting a void coalescence type of mechanism as has been reported for injection molded nylons. A diffuse damage zone, several millimeters in size, was observed at the crack tip for the glass-filled RIM nylon 6. The zone was observed to pulsate with the applied oscillating load. The growth of the damage zone volume with increasing crack length (and thus increasing stress intensity factor range) followed the Paris law, as did the crack growth rate data. The damage mechanism is attributed to void formation and microcracking at the fiber–matrix interface. The results of this study show that, for milled glass-reinforced RIM nylon 6, the crack growth rates were much more rapid than observed for injection-molded nylon 6 containing chopped glass fibers. This difference is attributed to the greatly reduced glass fiber lengths for the milled glasses.
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TL;DR: Etude experimentale par microscopie electronique analytique La rupture de la glace a grains fins entre −25 and −50C est une rupture transgranulaire par clivage Les pores agissent comme sites d'initiation for les marches de clivages as mentioned in this paper.
Abstract: Etude experimentale par microscopie electronique analytique La rupture de la glace a grains fins entre −25 et −50C est une rupture transgranulaire par clivage Les pores agissent comme sites d'initiation pour les marches de clivage
18 Aug 1989
TL;DR: The Failure Analysis Handbook as discussed by the authors provides a data base of known failure modes to draw from in forming his conclusions and provides a guide for procedures and lists other sources of information, including fractography of alloys.
Abstract: : Aircraft service failures of any type, from a simple rivet failure to complete engine failure, have the potential to result in loss of the aircraft and personnel. Accurate determination of the cause of the failure may yield information that will prevent similar future failures from occurring. It is helpful for the investigator to have a data base of known failure modes to draw from in forming his conclusions. The objective of this program was to update and augment the two primary Air Force failure analysis handbooks, Electron Fractography Handbook and SEM/TEM Fractography Handbook, published in 1965 and 1975, respectively, with a new 'Failure Analysis Handbook.' The new handbook includes fractography of alloys and conditions not previously covered in other handbooks. The handbook also is a guide for procedures and lists other sources of information. Keywords: Transmission electron microscopy; Scanning electron microscopy; Fracture/fatigue mechanics; Steel; Nickel alloys; Cleavage; Metallography; Decohesive rupture; Titanium alloys; Photomicrography; Military aircraft equipment failure.