Fracture Surface Topography Research Articles

Replaying the Fracture Process of a Failed Space Shuttle Orbiter Thruster

In order to rationalize the continued safe-flight of the Space Shuttle Orbiter fleet, root cause was urgently sought for the explosive failure of a Space Shuttle Orbiter reaction control system thruster that occurred on the test stand. To confirm the postulated failure scenario, the direction of crack propagation in the fuel chamber wall had to be determined. It was also necessary to determine if any of the failed thruster injector materials had been embrittled over time. Conventional fractography could not provide conclusive answers, but a quantitative 3D analysis of the topographies of the opposing fracture surfaces was able to reconstruct the entire fracture process and thereby confirm root cause. The work shows how a failure event can be replayed through fracture surface topography analysis, FRASTA, and how information on load conditions, relative crack growth rates, and fracture mechanics parameters may be extracted from fracture surfaces.

A Brief Discussion About Image Quality and SEM Methods for Quantitative Fractography of Polymer Composites

The methodology for fracture analysis of polymeric composites with scanning electron microscopes (SEM) is still under discussion. Many authors prefer to use sputter coating with a conductive material instead of applying low-voltage (LV) or variable-pressure (VP) methods, which preserves the original surfaces. The present work examines the effects of sputter coating with 25 nm of gold on the topography of carbon-epoxy composites fracture surfaces, using an atomic force microscope. Also, the influence of SEM imaging parameters on fractal measurements is evaluated for the VP-SEM and LV-SEM methods. It was observed that topographic measurements were not significantly affected by the gold coating at tested scale. Moreover, changes on SEM setup leads to nonlinear outcome on texture parameters, such as fractal dimension and entropy values. For VP-SEM or LV-SEM, fractal dimension and entropy values did not present any evident relation with image quality parameters, but the resolution must be optimized with imaging setup, accompanied by charge neutralization.

GeoFlow: A novel model simulator for prediction of the 3‐D channeling flow in a rock fracture network

A fluid flow experiment was conducted on a granite sample containing two intersecting fractures. At constant confining pressure, water was supplied to the sample via a single inlet port, and the effluent was collected using four isolated outlet ports. The flow rate varied widely among these ports, indicating the formation of 3‐D preferential flow paths (channeling flow), which likely occur in fractured rocks but have been considerably difficult to identify by existing methods. The novel concept of GeoFlow, a discrete fracture network model simulator in which fractures have a heterogeneous aperture distribution, has been developed to analyze such complex fluid flow. A fluid flow simulation was conducted using GeoFlow with aperture distributions within the two fractures, as determined using fracture surface topography data. Despite the simplicity of the simulation, GeoFlow revealed a 3‐D channeling flow within the sample, which explains the general trend of the uneven outflows in the experiment.

Study on Interior Fracture Property of High Strength Steel in Very High Cycle Regime

Based on the fracture mechanics theory and fracture surface topography analysis (FRASTA) method, the interior fracture property of a bearing steel in very high cycle regime was studied by means of rotary bending fatigue test. As a result, this bearing steel represents the duplex S-N curves characteristic, where the interior inclusion-induced fracture is the predominant fracture mode in very high cycle regime. The rough granular bright facet (GBF) area corresponding to smaller inclusion is usually formed in the lifetime larger than 106 cycles, whose formation progress can be interpreted as the slow crack nucleation based on decohesion of spherical carbide from the matrix. The fatigue property in the fish-eye region outside of GBF can be interpreted as the stable crack propagation progress and that outside of fish-eye is instable crack propagation progress. The stress intensity factor ranges of GBF and fish-eye, ΔKGBF and ΔKfish-eye, can be regarded as the threshold values of controlling stable propagation and instable propagation of interior crack, respectively.

Quantification of fatigue crack propagation of an austenitic stainless steel in mercury embrittlement

Liquid metals are expected to be used as nuclear materials, such as coolant for nuclear reactors and spallation targets for neutron sources, because of their good thermal conductivity and neutron production. However, in specific combinations, liquid metals have the potential to degrade structural integrity of solid metals because of Liquid Metal Embrittlement (LME). In this study, the effect of mercury immersion on fatigue crack propagation rate in SUS316 was investigated through fatigue tests with a notched specimen under mercury immersion. FRActure Surface Topography Analysis (FRASTA) with the measurement of the notch opening distance was performed to estimate the fatigue crack growth rate in mercury. The results showed that the fatigue crack growth rate was slightly higher in mercury than that in the air in the low cycle fatigue region. This suggests that the crack propagation is accelerated by mercury immersion in high stress imposition regions.

Microstructural correlations to micromechanical properties of polyamide-6/low density polyethylene-grafted-maleic anhydride/nanoclay ternary nanocomposites

Ternary nanocomposites were fabricated based on an optimized impact modified polyamide-6 (PA-6)/low density polyethylene grafted maleic anhydride (LDPE-g-MA) blend composition with varied concentration (∼0–6 wt.%) of organoclay, Cloisite 30B™. The microstructural attributes such as state of intercalation/exfoliation/crystalline organization and fractured surface topography of the nanocomposites by using electron microscopic and X-ray diffraction techniques. The X-ray diffraction studies have revealed that the crystallinity of the nanocomposites remained inappreciably affected. Dynamic mechanical analysis revealed an increase in T g of the nanocomposites relative to the neat PA-6 and the optimized PA-6/LDPE-g-MA blend matrix indicating the reinforcement effects/mechanical restrictions imposed by the nanoclay layers to the polymer chain mobility. The quasi-static mechanical response and micromechanics aspects concerning interfacial effects and stress-transfer efficiency of the nanocomposites using Halpin-Tsai, Hui-Shia, Takayanagi and Pukanszky models have been investigated. Micromechanical analysis based on minimalistic assumptions revealed interphase-thickness reduction at higher nanoclay content with a correspondence to the reduction in reinforcement-efficiency. Scanning electron microscopy of the cryo-fractured xylene-etched nanocomposite surfaces have indicated a nanoclay content dependent transition from homogeneous to inhomogeneous deformation assisted by the formation of random microfibril-like interconnected networks.

Comparative Studies of Fracture Surfaces of a Biomaterial with the Use of a Profilographometer and Confocal Microscope

The aim of the paper is to present comparative studies of the parameters of the fracture surface topography of titanium alloy, obtained by means of two techniques. The research equipment consisted of a Taylor Hobson profilographometer, Talysurf, and a confocal microscope, LEXT OLS 3000 by Olympus. By means of a contact and non-contact method, files of coordinates of the investigated surfaces were obtained, based on which some chosen stereometric parameters were calculated. The tests carried out as part of the study confirmed the usefulness and the possibility of using a confocal microscope as a modern instrument for evaluating the topography of non-planar surfaces. In the case of statistical parameters representing the whole surface under examination, very high convergence of the stereometric structure parameters was obtained, described by means of profilographometry and confocal microscopy methods.

The Fracture Research of Hexagonal Duralumin Nut

The microstructure, fracture surface topography and mode of hexagonal nut cracked in assembling under air pressure were analyzed with optical microscope and scanning electronic microscope, which are made in contrast with that of hexagonal nut cracked in man-made. The research results show that the man-made fracture of nut was of dimple shape and cracked in toughness mode, which accorded with the fracture behavior of 2Al2 duralumin material. The air-pressure fracture of nut was of right shape and cracked in brittle mode. The fracture mechanism is concluded that crack fountain is formed in surface of nut because of scoring during assembling and then the crack expands rapidly, leading to brittle fracture of the nut.

Survey of fractured SrTiO3 surfaces: From the micrometer to nanometer scale

Cross-sectional scanning tunneling microscopy was utilized to study fractured perovskite oxide surfaces. It was found that for the non-cleavable perovskite oxide, SrTiO3, atomically flat terraces could be routinely created with a controlled fracturing procedure. Optical, scanning electron and scanning tunneling microscopies, and a profilometer were used to obtain information from submillimeter to submicrometer scales of the fractured surface topography.

Fracture surface topography analysis (FRASTA)—Development, accomplishments, and future applications

Abstract In the late 1970s, Dr. George Irwin suggested to his colleagues at the University of Maryland that valuable information about a fracture event was recorded in fracture surface topography. Under his urging, Takao Kobayashi, an associate professor at the time, began quantifying and interpreting topographical features. Over the subsequent 30 years the procedures for quantifying and interpreting fracture surface topography grew continuously into an established technology that allows a fracture event to be reconstructed in microscopic detail. FRASTA (fracture surface topography analysis) has now been applied to achieve solutions to a wide variety of failure problems. This paper chronicles the historical development of FRASTA, recounts several notable achievements, and presents the plan for further development and future applications.

Morphological interpretations and micromechanical properties of polyamide-6/polypropylene-grafted-maleic anhydride/nanoclay ternary nanocomposites

Ternary nanocomposites were fabricated based on an optimized impact modified polyamide-6 (PA-6)/polypropylene grafted maleic anhydride (PP-g-MA) blend composition with varied concentrations (0–6 wt.% at a step of 2 wt.%) of organoclay, Cloisite 30B™. The morphological attributes such as state of intercalation/exfoliation/crystalline organization and fractured surface topography of the nanocomposites were characterized by transmission electron microscopy (TEM), wide angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) while the thermal characterizations were done by conducting differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The WAXD/DSC studies have revealed that the crystallinity of the nanocomposites remained unaffected. DMA revealed an increase in glass transition temperature ( T g) of the nanocomposites by ∼14–19 °C relative to the soft polypropylene (PP)-phase, by ∼7–12 °C relative to the neat matrix PA-6 and by ∼4–9 °C relative to the optimized impact toughened PA-6 matrix while simultaneously being accompanied by the appearance of a second phase T g peak progressively at higher temperatures as a function of nanoclay content, indicating the reinforcement effects/restrictions imposed by the nanoclay layers to the polymer chain mobility. The bulk mechanical response of the nanocomposites such as tensile, flexural and impact properties were studied and its related micromechanics aspects have been investigated using composite theories such as Halpin-Tsai, Hui-Shia, Takayanagi and Pukanszky models to analyze the interfacial effects and its role on the stress transfer efficiency. SEM analysis of fractured surface indicated that the failure mode of the nanocomposites undergoes a switch-over from interfacial-effects assisted fibrillation controlled ductile deformation to nanoclay induced soft PP-phase stiffened semi-ductile response via shear-lips formation.

Geostatistical downscaling of fracture surface topography accounting for local roughness

This study proposes a new geostatistical methodology that accounts for roughness characteristics when downscaling fracture surface topography. In the proposed approach, the small-scale fracture surface roughness is described using a “local roughness pattern” that indicates the relative height of a location compared to its surrounding locations, while the large-scale roughness is considered using the surface semivariogram. By accounting for both components–the minimization of the local error variance and the reproduction of the local roughness characteristics–into the objective function of simulated annealing, the fracture surface topography downscaling process was improved compared to standard geostatistical methodologies such as ordinary kriging and sequential Gaussian simulation. Downscaled topography data were then assessed in terms of prediction errors and roughness distribution.

Osteoplastic Biomaterials and Their Physical and Mechanical Properties

Objective. To perform comparative study of composition and strength properties of osteoplastic biomaterials subjected to technological processing. Material and Methods. Specimens of native (initial) and deproteinized bone tissue were analyzed. Strength properties of specimens were studied by single-axis static extension with automatic recording of load curves. Load-extension curves were used to calculate mechanical parameters: proportionality limit, strength limit, relative deformation before destruction, and the Young’s module. Dependence between a processing type and changes in the surface morphology, element composition, overall dimensions, and dry weight of specimens was identified. Results. All bone tissue specimens had small amount of deformation typical for fragile materials – 1 %. Proportionality limit for native bone tissue was 27 MPa, and that for deproteinized tissue –29 MPa. Strength limit did bone on the type of chemical processing of tissue and had the value of 80–90 MPa. Collagen presence influenced the Young’s module which was 110 MPa in deproteinized bone tissue, two-fold decreased from that in initial bone tissue (230 MPa). Topography of specimens and fracture surfaces were more pronounced after deproteinization. Conclusion. The study of physical and mechanical properties and composition of compact bone specimens gives an understanding of processing type influence on bone tissue structure and properties.

Bending Fatigue Strength of Austenitic Stainless Steel SUS316 in Mercury

Liquid mercury target system for spallation neutron source is installed at Materials and Life Science Experimental Facility in Japan Proton Accelerator Research Complex (J-PARC), which will promote innovative science. Austenitic stainless steel SUS316 for a structural material of the target vessel is contact with mercury, and imposed by cyclic pressure that is induced by pulsed proton beam injection at 25Hz. Therefore, it is important from the viewpoint of the structural integrity to investigate the effect of mercury on fatigue behavior of the structural material. Bending fatigue tests in mercury and air were performed to evaluate the effect of mercury on fatigue behavior. FRActure Surface Topography Analyses (FRASTA) were carried out to evaluate the change in fracture morphology with mercury. It was confirmed that the fatigue strength was decreased by mercury immersion in low cycle region less than 105 cycles and intergranular fracture surface was observed, while in high cycle region the mercury immersion effect was hardly recognized.

Quantifying the effect of fracture surface topography on the scattering of grain boundary segregation measurement by Auger electron spectroscopy

The aim of this paper is to estimate the effect of the geometrical orientation of grain boundary facets on the quantification of grain boundary segregation by Auger electron spectroscopy (AES) on an in-situ fractured surface. Phosphorus grain boundary segregation (PGBS) was studied on 17 different samples (including 3 different steels and 12 different thermal treatments) using a MAC2 analyzer from Riber company. For each sample, 14 to 41 grain boundary facets were analyzed. It is demonstrated that there is proportionality between the PGBS mean value and the PGBS standard deviation obtained on one particular sample: for each sample, the PGBS standard deviation represents approximately 40% of the PGBS mean value. The topography of a typical purely intergranular fracture surface was determined by 3D stereographic observation in a SEM. The influence of surface topography on Auger quantification was then evaluated using the Auger quantification equations. The orientation of grain boundary facets with respect to the primary beam and the Auger analyzer was taken into account. The result is that, considering a homogeneous PGBS on all the grain boundary facets, a large scattering (~ 45%) of the PGBS quantification by AES can be accounted for by a purely geometrical effect (orientation of each facet with respect to the primary beam and to the Auger analyzer). This geometrical effect is nevertheless strongly dependant on the spectrometer geometry (respective position of primary beam, sample and Auger analyzer with respect to each other) and could be reduced by optimizing the relative positions of primary beam, sample and Auger analyzer. The topographical analysis was extended to the case of the well-known CMA (Cylindrical Mirror Analyzer). The scattering of the PGBS measurements with Auger spectrometers fitted with a CMA perpendicular to the fracture surface is expected to be much smaller.

Microscopical Investigations of PEDOT:PSS Thin Films

AbstractElectron microscopy studies are used to explore the morphology of thin poly(3,4‐ethylenedioxythiophene) and polystyrene sulfonate acid (PEDOT:PSS) films. The figures show that the films are composed of grains with diameters in the range of about 50 nm. Energy dispersive X‐ray spectroscopy analysis reveals that individual grains have a PEDOT‐rich core and a PSS‐rich shell with a thickness of about 5–10 nm. Atomic force microscopy (AFM) is then used to analyze the topography of fracture surfaces of ruptured PEDOT:PSS tensile specimens. These AFM scans also show that the films are composed of grains dispersed in a matrix. The investigations presented herein yield a picture of PEDOT:PSS morphology with unprecedented clarity.

Fractal Dimension of Grain-boundary Fracture for Characterization of High-temperature Fracture in Heat-resistant Alloys

The fractal dimension of the grain-boundary fracture, Df, (2<Df<3), which represents the fracture surface pattern with grain-boundary microcracks in three-dimensional space, is proposed for characterization of high-temperature fracture in materials. The value of Df as well as its two dimensional value, Dfp (the fractal dimension of the grain-boundary fracture surface profile, 1<Dfp<2), was estimated in the length scale range more than about one grain-boundary length using the height data of fracture surfaces of heat-resistant alloys obtained by the stereo matching method. The value of Df increased with increasing fractal dimension of the grain-boundary surface profile (DGB, 1<DGB<2) in the specimens of the HS-21 alloy ruptured at 1089 K. Both rupture life and creep ductility increased with increasing value of Df in these specimens. Similar results were obtained by the two-dimensional fractal analysis on other specimens of cobalt-base, nickel-base and iron-base heat-resistant alloys. Creep fracture process including the growth of the main creep crack was examined by the fractal analysis using the fractal dimension map (FDM, a color-coded map) on the surface notched specimens. The result of the fractal analysis was compared with that of the FRASTA (fracture surface topography analysis) in the Inconel X-750 alloy. The fractal analysis used in this study is more convenient and more advantageous than the FRASTA, and is widely applicable to the investigation of high-temperature fracture in materials.

Mechanical characterization of PEDOT:PSS thin films

By tensile testing the mechanical properties of thin films of the intrinsically conductive poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) under different relative humidities are investigated. It can be shown that the fracture behaviour strongly depends on humidity and reaches from brittle to plastic. The fracture surfaces are first investigated by scanning electron microscopy (SEM). The surfaces change from smooth at 23% rH to rough with shear lips for samples tested at 55% rH. Atomic force microscopy then reveals the topography of fracture surfaces at the nanometer scale and thus gives insights into the morphology of PEDOT:PSS thin films. By combining the experimental findings of the tensile tests and the AFM scans a micromechanical model for the deformation behavior of PEDOT:PSS can then be derived.

A FRACTOGRAPHICAL STUDY ON BORON ADDED ARMOR STEEL DEVELOPED BY ALLOYING AND HEAT TREATMENT TO UNDERSTAND ITS BALLISTIC PERFORMANCE

ABSTRACTFractographical examinations present a good relationship between fracture surfacetopography and basic rupture mechanism. Fracture consists of crack formation (cracknucleation) and crack growth (crack propagation). Many parametres such as type ofloading, sensitivity of materials to crack play an important role on failure. Fracture inengineering alloys can occur by a transgranular (through the grains) or an intergranular(along the grain boundaries) fracture path.In this study newly developed boron added armor steel has been rolled to form sheetproduct. Heat treatment series including austenitization, quenching and then temperinghave been applied on boron added armor steel respectively. The effects of formedmicrostructures on mechanical properties have been studied extensively. Furthermorefailure mechanism has been determined through fractografical examinations by usingScanning Electron Microscopy (SEM). due to its high resolution. In general SEMexaminations are an important part of failure analysis.Failure analysis and type of fracture provide also a good approach to understand theballistic behaviour of armor steel. When the material is exposed to any kind of impactloading as performed by kinetic penetrator etc., it is obvious that the failure mode willgive information about its ballistic performance.

Structure and mechanical properties of gradient PVD coatings

Abstract The paper presents investigation of the Ti(C, N) and (Ti, Al)N gradient coatings deposited with use of the cathodic arc evaporation CAE-PVD method on sintered tool materials: cemented carbides, cermets and Al 2 O 3 + TiC oxide tool ceramics. The investigation includes the metallographic analysis on the scanning electron microscope (SEM). The X-ray qualitative microanalysis and surface distribution analysis of elements in the investigated materials were made using the EDS X-ray energy dispersive radiation spectrometer. Moreover the investigation includes analysis of the mechanical and functional properties. Tests of the coatings adhesion to the substrate material with use of the scratch test and surface roughness tests were done both before depositing the coatings and after completing the PVD process. It has been showed that investigated materials are characteristic of the dense, compact structure and their fracture surface topography attests to their high brittleness, characteristic especially for the oxide ceramic materials. The results of roughness and microhardness tests confirm the advantages of the multicomponent (Ti, Al)N and gradient Ti(C, N) coatings. As results of the examination of coating microhardness it has been found that multicomponent and gradient coatings on the investigated materials causes the 35–76% increase of microhardness value. Depositing the wear resistant coatings onto the tool cemented carbide, cermet, and oxide tool ceramics results in a significant increase of the surface layer microhardness, contributing most probably in this way in machining to the decrease of the wear intensity of cutting tools’ flanks made from cemented carbide, cermet and tool ceramics.