Auswahl der wissenschaftlichen Literatur zum Thema „Statistical fractography“

Abstract In this paper, an image processing technique to quantitatively analyze abraded, torn and fatigue failed surfaces is described. The image surfaces were represented in terms of a closed set of orthogonal polynomials. The significant orthogonal effects were measured and combined to represent the local texture, called pronum. The frequency of occurrence of the pronums is the prospectrum, a global descriptor. Various statistical parameters were calculated from the prospectrum and correlated to the ridge spacings on abraded surfaces. The statistical closeness between various textured surfaces was also quantified. Using the image processing technique, the laborious procedure involved for quantification especially of irregular microfeatures has been shown to be overcome. Author to whom correspondence should be addressed.

The study verifies the sensitivity of selected construction materials (S235JR structural steel and 1.4301 stainless steel) to the statistical size effect. The P–S–N curves were determined experimentally under high-cycle fatigue conditions for two specimen sizes (mini-specimen and standard specimen). The results were analyzed using a probabilistic model of the three-parameter Weibull cumulative distribution function. The analysis included the evaluation of the technological process effects on the results based on the material microstructure near the surface layer and the macro-fractography. The differences in the susceptibility to the size effect validated the applicability of the test method to mini-specimen and showed different populations of the distribution of critical material defects.

This study was conducted to investigate fatigue behavior of friction stir welding (FSW) butt joints for 6156-T6 aluminum alloy. The detail fatigue rating (DFR) values of 6156-T6 FSW joints is obtained based on statistical analysis of fatigue tests. The micrographs of weld structure were observed by optical microscope (OM), Fatigue fractography was researched under scanning electron microscope (SEM). The results indicate that DFR value of 6156-T6 FSW joints is 153.31MPa. Fatigue property of FSW butt joints is sensitive to the microstructural features, such as nugget zone (NZ), thermo mechanically affected zone (TMAZ) and heat affected zone (HAZ). The hardness distributions of the FSW joints reveal W-shaped profiles. Fractography shows that fatigue cracking is initiated at weak-bonding defects, which are located at the root site of the butt joint. The weak-bonding defects have obvious influence on the fatigue properties of friction stir welding.

We suggest that the apparent interfacial fracture toughness (KA) may be estimated by fracture mechanics and fractography. This study tested the hypothesis that the KA of the adhesion zone of resin/ceramic systems is affected by the ceramic microstructure. Lithia disilicate-based (Empress2-E2) and leucite-based (Empress-E1) ceramics were surface-treated with hydrofluoric acid (HF) and/or silane (S), followed by an adhesive resin. Microtensile test specimens (n = 30; area of 1 ± 0.01 mm2) were indented (9.8 N) at the interface and loaded to failure in tension. We used tensile strength (σ) and the critical crack size (c) to calculate KA (KA = Yσc1/2) (Y = 1.65). ANOVA and Weibull analyses were used for statistical analyses. Mean KA (MPa·m1/2) values were: (E1HF) 0.26 ± 0.06; (E1S) 0.23 ± 0.06; (E1HFS) 0.30 ± 0.06; (E2HF) 0.31 ± 0.06; (E2S) 0.13 ± 0.05; and (E2HFS) 0.41 ± 0.07. All fractures originated from indentation sites. Estimation of interfacial toughness was feasible by fracture mechanics and fractography. The KA for the systems tested was affected by the ceramic microstructure and surface treatment.

The natural fiber reinforced polymer composites are recognized as an alternative to wood and plastics in recent years. The natural plant fibers are extracted from various parts of the tree and are used in polymer composites.The present investigation is focused on the improvement of tensile strength of coir-vinyl ester composites by impregnation of bio particulates such as alumina, red mud and rice husk. The fracture method of composite specimens are analyzed with the help of scanning electron micrographs.The observed range of tensile strength values are studied using statistical procedure and non linear regression models are developed.

Debonding of zirconia cantilevered resin-bonded fixed dental prostheses (RBFDPs) remains the main treatment complication, therefore, the present in vitro study aimed to evaluate the effect of different surface pretreatments on the bonding of zirconia RBFDPs. Eighty milled zirconia maxillary central incisors, with complementary zirconia cantilevered RBFDPs, were randomly subjected to four different surface pretreatments (n = 20): as-machined (AM); airborne-particle abraded (APA); coated with nanostructured alumina coating (NAC); incisor air-abraded and RBFDP coated (NAC_APA). After bonding, half of each group (n = 10) was stored in deionized water (150 days/37 °C), thermocycled (37,500 cycles, 5–55 °C), and cyclically loaded (50 N/1.2 × 106). Load-bearing capacity (LBC) was determined using a quasi-static test. Additionally, finite element analysis (FEA) and fractography were performed. t-test and one-way ANOVA were used for statistical-analysis. Before aging, the NAC group provided superior LBC to other groups (p < 0.05). After aging, the AM specimens debonded spontaneously, while other groups exhibited comparable LBC (p ˃ 0.05). The FEA results correlated with the in vitro experiment and fractography, showing highly stressed areas in the bonding interface, cement layer, and in RBFDP’s retainer wing and connector. The NAC RBFDPs exhibited comparable long-term bonding performance to APA and should be regarded as a zirconia pretreatment alternative to APA.

Effect of alloy composition on impact tensile properties [Formula: see text] in Al - Mg - Si base alloys was investigated by means of the split Hopkinson pressure bar method. As a result of the impact test, it was proved that the nominal stress for 5% plastic strain was not changed by changing the strain rate regardless of the alloy composition. In the impact test, the elongation was decreased with increasing the amount of excess Si , while that was increased by the addition of Cu . Fractography revealed that the reduction of the elongation in the excess Si alloy was caused by the change of the fracture mode from the mixture of transgranular and intergranular fracture to the intergranular fracture.

There are at present several applications where high strength ceramics have replaced metals that are subjected to high speed impact from projectiles. This requires an evaluation of behavior of ceramics under impact at high strain rates. This current study provides information on high strain-rate behavior of alumina tested in shear using torsional Hopkinson bar. Dynamic stress-strain curves were generated to investigate deformation behavior prior to fracture while fractography of the broken specimens was carried out to establish the mode of failure. The results of this investigation are similar to what is obtainable in metallic materials in which mechanism of damage is controlled by strain localization and formation of adiabatic shear bands.

The aim of this in vitro study was to investigate the fracture resistance, fracture failure pattern, and fractography of four types of chairside computer-aided design/computer-aided manufacturing (CAD/CAM) restoration materials in teeth and titanium abutments fabricated using a standardization method. An artificial mandibular left first premolar prepared for all-ceramic crown restoration was scanned. Forty extracted mandibular molars and cylindrical titanium specimens were milled into a standardized shape. A total of eighty CAD/CAM restoration blocks were milled into a crown and twenty pieces of each lithium disilicate (LS), polymer-infiltrated-ceramic-network (PICN), resin nano ceramic (RNC), and zirconia-reinforced lithium silicate (ZLS) materials were used. Crowns were bonded to abutments, and all specimens underwent thermal cycling treatment for 10,000 cycles. Fracture resistance was measured using a universal testing machine and fracture failure patterns were analyzed using optical microscopy and scanning electron microscopy. Statistical differences were analyzed using appropriate ANOVA, Tukey HSD post hoc tests, and independent sample t-tests (α = 0.05). The results indicated that, in both teeth abutments and titanium abutments, the fracture resistances showed significantly the highest values in LS and the second highest in ZLS (p < 0.05). The fracture resistances based on teeth abutments and titanium abutments were significantly different in all the CAD/CAM restoration materials (p < 0.05). There are statistically significant correlations between the types of materials and the types of abutments (p < 0.05). Each of the different materials showed different fracture failure patterns, and there was no noticeable difference in fractographic analysis. Lithium disilicates and zirconia-reinforced lithium silicates exhibited statistically high fracture resistance, indicating their suitability as restoration materials for natural teeth or implant abutments. There were no distinct differences in the fracture pattern based on the restoration and abutment materials showed that the fracture initiated at the groove where the ball indenter was toughed and propagated toward the axial wall.

Modern aircraft are designed using the damage tolerance concept. Fatigue cracks will be occurred at the initial flaw such as micro flaws in the material and scratches during the material manufacturing process. And stress concentration on notches, fillets and rivet holes under random loads caused to initiate the crack. This crack will propagate by repeated loads and finally failure. Therefore aircraft parts must be performed the damage tolerance test to prove the safety of the design life under the loads during operation. In this study, we have tested and analyzed the crack propagation behavior of aluminum alloy 2024-T3 plate under random loads. The crack lengths measured by the fractography analysis were compared to the analysis results with the retardation effect.

The main goal of this project was to compare the changes in statistical variation and Weibull characteristics of the strength of glass rods as modified by heat treatment with and without an ion exchange bath. Several sample groups of 30 sodium borosilicate glass rod specimens were heat treated at various temperatures in air and in a potassium nitrate salt bath to induce an ion exchange process. All samples were then tested to failure in 4-point bending to assess the resulting Modulus of Rupture (MOR). Statistical analysis techniques and Weibull analysis were used to study the variations which occur within and between strength distributions of each sample group. A smaller sampling of test groups was subjected to fractographic analysis to study the effect of ion exchange on fracture features. The data shows that the ion exchange process caused a statistically significant increase in the strength of the glass rods. Samples which were heat treated do not show any significant changes in average strength. The fractographic analysis suggests that no changes in fracture morphology occurred as a result of ion exchange process, and that the critical flaw size population was not significantly different.
Master of Science

Cette étude vise à déchiffrer la rugosité des surfaces de rupture pour déduire les propriétés de fracture des matériaux et révéler les mécanismes de défaillance sous-jacents dans les polymères, en se concentrant spécifiquement sur le PMMA (polyméthacrylate de méthyle). Compte tenu de la dépendance en temps de son comportement, de sa sensibilité à la température et d'une ténacité dépendante de la vitesse, nous avons développé des méthodologies et utilisé des outils avancés d'analyse fractographique pour explorer les caractéristiques morphologiques de ses surfaces de rupture. Nous avons généré une gamme de surfaces sous différents régimes de croissance de fissures, et des mesures optiques couplées à la corrélation d'images numériques (DIC) nous ont permis de calculer la vitesse de fissuration et la ténacité.Notre analyse a identifié des caractéristiques de surface distinctes à différentes vitesses de fissuration : des facettes de fragmentation dans la croissance lente, des surfaces rugueuses avec des microfissures (marques coniques) et des régions lisses d'apparence brumeuse ("mist") dans la croissance rapide, ainsi que des lignes d'arrêt de fissure à des vitesses critiques entre les deux. Pour passer de l'analyse qualitative à l'analyse quantitative, nous avons utilisé la profilométrie pour créer des cartes topographiques des surfaces de rupture, qui ont été analysées pour calculer des métriques de rugosité et l'échelle de longueur d'endommagement, une métrique de fractographie statistique liée a la taille de la zone d'endommagement. Ces cartes ont facilité l'utilisation de techniques de machine learning pour classifier les caractéristiques de surface et prédire la vitesse de fissuration et la ténacité.Nos résultats mettent en évidence une vitesse critique (~180 m/s) marquant une transition de la région "mist" à celle des marques coniques, corrélée à une augmentation de la ténacité. Cette transition de phase est illustrée par une forte augmentation de l'échelle de longueur de d'endommagement et une augmentation locale de la température en pointe de la fissure, atteignant la température de transition vitreuse du PMMA. Ces observations contribuent à une compréhension plus approfondie des mécanismes d'augmentation de la ténacité dans les polymères
This study aims to decipher fracture roughness to infer material fracture properties and reveal underlying failure mechanisms in polymers, specifically focusing on PMMA (polymethyl methacrylate). Given the unique time-dependent behavior, temperature sensitivity, and velocity-dependent fracture toughness of PMMA, we developed methodologies and used advanced fractographic analysis tools to explore the morphological features of fracture surfaces. We generated a range of fracture surfaces under varied crack growth regimes, and optical measurements coupled with DIC (Digital Image Correlation) allowed us to compute crack velocity and fracture toughness.Our analysis identified distinct surface features across different crack velocities: fragmentation facets in slow growth, conic marks and mist regions in fast growth, and crack arrest lines at critical velocities in between. Transitioning from qualitative to quantitative analysis, we used profilometry to create topographic maps of fracture surfaces, which were analyzed to compute roughness metrics and damage length scale, a metric from statistical fractography correlated to the process zone size. These maps facilitated the use of deep learning techniques to classify surface features and predict crack velocity and toughness.Our findings highlight a critical velocity (~180 m/s) marking a transition from mist to conic marks, correlating with an increase in toughness. This phase transition is evidenced by a sharp rise in the damage length scale and local temperature increase at the crack tip, reaching the glass transition temperature of PMMA. These insights contribute to a deeper understanding of the toughening mechanisms in polymers

L’utilisation de l’énergie nucléaire nécessite des solutions sûres pour le stockage des déchets radioactifs. Une solution proposée pour les déchets radioactifs de haute activité est le stockage dans des formations géologiques profondes à faible perméabilité, telles que des argilites. En France, la faisabilité et la sureté à long terme de cette solution est étudiée dans l’URL (Underground Research Lab - Laboratoire de Recherche Souterrain) de Bure par l’Andra, l’agence nationale de gestion des déchets radioactifs. Motivé par ce défi, nous étudions ici les propriétés de rupture de l’argillite Callovo-Oxfordian (COx) présent sur le site de Bure. La propagation des fissures est le principal mécanisme de rupture des matériaux sous traction. Cependant, dans les matériaux anisotropes comme les argilites, le comportement des fissures lors de leur phase d’initiation, puis de leur propagation reste mal compris. Par conséquent, ces travaux visent également à améliorer notre compréhension des mécanismes élémentaires de rupture dans les matériaux anisotropes, à travers l’exemple de l’argilite COx. Dans ce contexte, nous avons effectué une caractérisation systématique des propriétés de rupture de l’argilite COx par test mécanique tant pendant la phase de propagation de la fissure (via la mesure de la ténacité dans différentes directions du matériau, et pour différents niveaux de teneur en eau), ainsi que dans la phase d’initiation (par la mesure de sa contrainte cohésif dans différentes directions également). Nous avons ensuite montré que nous pouvions mesurer ces propriétés de rupture à partir d’une analyse statistique des surfaces de rupture obtenues.Nous avons ensuite appliqué cette nouvelle méthode de caractérisation des matériaux aux fissures générées lors de l’excavation des galeries souterraines et extraites dans l’URL à 490 m de profondeur. Ceci nous a permis de mesurer les propriétés de rupture de l’argilite COx dans des conditions in situ. Enfin, la caractérisation fine des propriétés anisotropes de rupture de l’argilite (COx) nous a permis de calibrer un modèle visant à expliquer la présence de fissures autour des ouvrages souterrains. En particulier, notre modèle rend compte de façon qualitative la forme et la taille de la zone endommagée observée autour des ouvrages, en s’appuyant sur un mécanisme original de fissuration sous chargement compressif. Pour conclure, nous pensons que ces résultats pourront contribuer à la conceptions d’ouvrages souterrains plus sûrs
The use of nuclear energy requires safe solutions for the storage of radioactive waste. A solution proposed for high activity radioactive waste is the storage in deep low permeability geological formations such as claystones. In France, the feasability and safety of this solution is investigated in the Bure URL (Underground Research Lab) by Andra, the French agency for the management of radioactive wastes. Motivated by this challenge, we explore here the fracture properties of the Callovo-Oxfordian (COx) claystone present in Bure. Crack propagation is the main mechanism leading to material failure under traction. However, in anisotropic materials like claystone, the behavior of cracks both during their initiation and their propagation phase remains poorly understood. As a result, this work aims also at improving our understanding of the mechanisms of fracture in anisotropic materials, through the example of the COx claystone. In addition to that, the determination of the fracture properties of rocks in their in-depth conditions is a very diffcult challenge. We will show here that this diffculty can be overcome by analysing the roughness of the in-depth fractures. We will start this study by a systematic characterization of the fracture properties of the COx claystone from fracture tests performed in the laboratory. We will investigate both the crack propagation phase (through the measurement of the toughness in different directions of the material, for different water content levels) as well as the initiation phase (through the measurement of the cohesive strength in different directions too). We will then show how to measure these material parameters from a statistical analysis of the resulting fracture surfaces. In a second step, we will apply this newly developped method of material characterization to fractures produced during the excavation of the gallery and extracted in the URL at 490 m deep. This analysis will provide the fracture properties of COx claystone in in-situ conditions. Finally, the detailed characterization of the fracture properties of the COx claystone will be used in structural calculations to better understand the origin of the fractures located around the gallery. In particular, we will propose an original mechanism of tensile crack initiation under dominantly compressive loading conditions that allows us to capture the shape and size of the damaged zone observed around the gallery. On the long term, we believe that our work will help to the design of safer galleries dedicated to the storage of nuclear waste

The demand for flat glass is high and increasing significantly in the building industry as a direct result of architectural requirements for lightness, transparency and natural light. Current architectural trends require glass in curvilinear forms for smooth free-form façades. Two principal challenges arise from this: to cost-effectively produce the desired curvature and; to ensure its safe performance after exposure to ageing. The recent availability of high strength glass provides an opportunity to address the first challenge by developing cold bent glass. Cold bending involves the straining of relatively thin glass components, at ambient temperatures, and is a low energy and cost effective manner of creating curvilinear forms. However, cold bending is not yet widely established as a reliable method. The aim of this thesis is to develop the understanding of cold bent glass during the bending process and to evaluate its post-ageing performance. This thesis, firstly, investigates the mechanical response of monolithic glass plates during the cold bending process. The stability of cold bent glass is investigated experimentally by bending it in double curved anticlastic shapes. A parametric numerical analysis involves different boundary conditions, geometrical plate characteristics and bending parameters. The principal outcome is that a local instability, now termed cold bending distortion, occurs when certain displacement limits are exceeded and could degrade the optical quality of the glass. An evaluation procedure is also formulated to set limits and aid designers/manufacturers to predict the mechanical response and the optical quality of the glass. Cold bent glass is subjected to permanent bending stresses throughout its service life and therefore, its strength degradation after ageing needs to be quantified. Analytical, experimental and numerical investigations are undertaken in this thesis to identify the most effective method for estimating glass strength (evaluation of destructive tests, required number of specimens, statistical analysis methods and sub-critical crack growth). The limited availability of naturally aged toughened glass and the absence of a reliable ageing standard impede the evaluation of its aged performance. Therefore, a parametric experimental investigation of artificial ageing methods on glass is undertaken in this thesis. A procedure for the evaluation of the strength of aged glass is finally, formulated to allow the selection of artificial ageing parameters that correspond to a target level of erosion. The knowledge on artificial ageing and strength prediction acquired above is finally implemented on different types of glass to determine their strength after ageing and assess their safe use in cold bending / load bearing applications. The investigation showed that fully toughened glass has a superior performance to chemically toughened or annealed glass. Overall, the research presented in this thesis demonstrates that high quality cold bent toughened glass can be created when certain applied displacement limits are respected. These can be used as a safe, cost-effective and energy efficient replacement to the more conventional hot bent glass. However, cold bending / load bearing applications in which the stressed glass surface is exposed to ageing, require glass with a relatively high case depth such as fully toughened or bi-tempered glass.

An update is presented of the activities of the American Society for Testing and Materials (ASTM) Committee C-28 on Advanced Ceramics. Since its inception in 1986, this committee, which has five standard producing subcommittees, has written and published over 32 consensus standards. These standards are concerned with mechanical testing of monolithic and composite ceramics, nondestructive examination, statistical analysis and design, powder characterization, quantitative microscopy, fractography, and terminology. These standards ensure optimum material behavior with physical and mechanical property reproducibility, component reliability, and well-defined methods of data treatment and material analysis for both monolithic and composite materials. Committee C-28 continues to sponsor technical symposia and to cooperate in the development of international standards. An update of recent and current activities as well as possible new areas of standardization work will be presented.

Abstract Current design lives for US Air Force turbine engine materials are based on a 1 in 1000 rate of nucleation of an engineering sized crack (B0.1). These lives are determined from models fitted to test coupon fatigue data at many different loading conditions. It has been shown that this methodology can sometimes lead to excess conservatism, and it often does not fully incorporate understanding of the mechanisms that drive crack initiation, growth, and fracture. A mechanism based probabilistic life forecasting methodology has been previously proposed with the objective to improve the prediction of minimum fatigue life or design life through understanding of the type and frequency of the material mechanisms that lead to early or immediate fatigue crack initiation. An approach is proposed and demonstrated for the estimation of probabilistic mechanism-based design life prediction confidence bounds. These confidence bounds on the calculated B0.1 or minimum life predictions are dependent on the quality and quantity of the data used in the analysis. The effect of additional data from either small crack growth tests or microstructural characterization or fractography analysis on the extent of the calculated confidence bounds is shown. The analysis presented can ultimately be used to describe a relationship between the required confidence in the design life predictions to the cost of the test program required to collect the necessary data. Comparisons are made between data requirements and the level of confidence in empirical statistical predictions from fatigue test data and the new probabilistic mechanism-based design life predictions for laboratory specimens in a turbine engine material.

Strength characterization and analysis of fracture size effect in ultrananocrystalline diamond (UNCD) thin films are presented. In this work, we report the changes in mechanical properties of UNCD by the addition of nitrogen gas to the Ar/CH4 microwave plasma. Both undoped and doped UNCD films show a decrease in fracture strength with an increase in specimen size. The strength data, obtained by using the membrane deflection experiment (MDE) developed at Nothwestern University, is interpreted using Weibull statistics. The capability of the theory is examined in conjunction with detailed fractographic analysis. The Weibull parameters are estimated by maximum likelihood estimation (MLE) based on 480 tests when the specimen volume varies from 500 to 1600 cubic microns. The results show that one can predict the fracture strength of a component possessing any arbitrary volume to within ±3% from the fracture strength identified from the tested specimens. The failure mode of UNCD is suggested to be volume controlled.

The current work aims to point out the influence of plastic strain history, due to reel-lay installation, on the fatigue resistance of welded SMLS (seamless) steel pipes used for fabrication of Steel Catenary Risers (SCRs) for oil and gas development. A C-Mn steel X65 pipe 10.75″ (273.1 mm) outside diameter (OD) and 25.4 mm wall thickness (WT) was chosen for this program. The Welding Procedure designed for girth welds manufacturing involved the use of Lincoln STT-GMAW™ (Surface Tension Transfer–Gas Metal Arc Welding) process for the root pass and SAW (Submerged Arc Welding) process with twin wire configuration for the fill and cap passes. This welding procedure presents a special post-weld finishing treatment, which consists in flapping the inner and outer weld overfills to produce a flush profile between weld metal and outer/inner pipe surfaces. The experimental approach was focused on quantifying the effect of accumulated plastic deformation using two different reeling frames simulating the same laying vessel: the Technip’s Apache. In this program, two reeling trials were performed at Heriot Watt University, Edinburgh, U.K., and two other trials at Stress Engineering Services, Houston, U.S.A. Then, the strained specimens were full scale fatigue tested at TenarisTamsa R&D facilities. Those results have been compared with fatigue results obtained on unstrained specimens. Post-tests fractographic investigations were systematically performed on all samples to identify the causes for fatigue initiation. The results were statistically analyzed to determine which standard fatigue design curves best represent the measured S-N fatigue endurance. Finally, the results were also compared with the available literature.