Facet Size Research Articles

Initiation and Propagation Processes of Internal Fatigue Cracks in β Titanium Alloy Based on Fractographic Analysis

Uniaxial fatigue tests were conducted for a β titanium alloy Ti-22V-4Al up to a very high cycle fatigue (VHCF) regime. The initiation and propagation processes of the internal fatigue cracks were investigated using 3D fractographic analysis. Multiple facets were observed at the crack initiation site. Three facet initiation models were proposed based on the surface appearances and the 3D facet bonding patterns of the multiple facets, and the major facet was determined to be the true crack initiation site. Using the size of the major facet, a Tanaka–Akiniwa model, which can determine the material constants for the Paris law using only conventional fatigue tests, was applied to reveal the propagation process of the internal cracks. A reverse fatigue life prediction was also conducted to evaluate the accuracy of the material constants obtained using the Tanaka–Akiniwa model. When the facet initiation models were applied, the predictions showed less deviation and better agreement than when the facet initiation process was not considered. The findings of this study indicate that the formation of multiple facets in β titanium alloys is sequential rather than simultaneous.

A multi-barrier model assisted CAFE method for predicting ductile-to-brittle transition with application to a low-carbon ultrahigh-strength steel

The conventional micromechanical approaches today are still not able to properly predict the ductile-to-brittle transition (DBT) of steels because of their inability to consider the co-operating ductile fracture and cleavage mechanisms in the transition region, and simultaneously to incorporate the inherent complexity of microstructures. In this study, a complete methodology with coupled cellular automata finite element method (CAFE) and multi-barrier microcrack propagation models is presented to advance the prediction of DBT. The methodology contains three key elements: (i) a multiscale CAFE modelling approach to realize the competition between ductile damage and cleavage fracture and embrace the probabilistic nature of microstructures, (ii) a continuum approach to estimate the effective surface energy for a microcrack to penetrate over particle/matrix interface, and (iii) a method to calculate the effective surface energy for the microcrack to propagate across grain boundaries. The prediction of DBT therefore needs only (1) the stress-strain curves tested at different temperatures, (2) the activation energy for DBT, (3) the ratio between the size of cleavage facets and cleavage-initiating defects, and (4) key statistical distributions of the given microstructures. The proposed methodology can accurately reproduce the experimental DBT curve of a low-carbon ultrahigh-strength steel.

Micro-refractive optical elements fabricated by multi-exposure lithography for laser speckle reduction.

Laser speckle reduction with a macro refractive optical element (mROE) is restricted by the limited entrance facet size of light pipe. Here, we have fabricated a micro-ROE (μROE) that incorporates three-dimensional micro-optical structures. The μROE with 2 × 2 duplicated multi-level cells is made of SU-8 photoresist with the help of multi-exposure lithography process. When the μROE works together with the mROE, objective speckle contrast is reduced to 0.2, where the light source is a low-coherence multimode laser diode. In principle, more speckle reduction can be obtained by fabricating μROEs with more cells and larger height differences among the cells.

Association of Lunate Morphology With Progression to Scaphoid Fracture Nonunion.

Background: The purpose of our study was to review a series of patients with scaphoid fractures to determine whether there was an association between lunate morphology and progression to delayed union or nonunion when treated operatively or nonoperatively. Secondary aims included evaluation of the relationship between lunate morphology and scaphoid fracture location. Methods: A retrospective review of all patients with a diagnosis of scaphoid fracture was performed at our institution between 2014 and 2017. Medical records and radiographs were evaluated to determine lunate morphology, scaphoid fracture location, treatment, and time to union. Differences between groups were determined using χ2 analysis with significance set at P <.05. Multiple logistic regression analyses were used to evaluate scaphoid union in the setting of lunate morphology when controlling for confounders. Results: A total of 169 patients were included; 45.0% (n = 76) of patients had type I lunate morphology, and 55.0% (n = 93) had type II. In all, 64.5% (n = 49) of patients with type I lunate and 68.8% (n = 64) with type II lunate had a fracture at the scaphoid waist. Among all patients with a scaphoid fracture, type II lunates were more likely than type I lunates to progress to nonunion when treated both operatively and nonoperatively (18.3% vs 4.0%, P = .0042). Lunate facet size was not shown to be a significant risk factor for nonunion among patients with a type II lunate (P = .4221). Conclusions: Patients with a scaphoid fracture and type II lunate morphology were more likely to progress to nonunion than patients with a type I lunate.

Comparative Study of Microstructure and Mechanical Properties of X80 SAW Welds Prepared Using Different Wires and Heat Inputs

The present work investigated the effect of weld composition and welding heat input on the microstructure and mechanical properties of two submerged arc welded (SAW) joints of API 5L-X80 pipeline steel. The weld metals were joined by two welding consumables (one is rich in C, Ni, Cr, Mo) under different welding heat inputs (20-22 and 34-36 kJ/cm for single-wire and triple-wire processes, respectively). The triple-wire welding procedure with less C, Ni, Cr, Mo alloy contents favors the formation of acicular ferrite (AF), whereas single-wire welding procedure with increased C, Ni, Cr, Mo contents promotes the formation of lath bainite (LB). Nanoindentation is used to evaluate the property of different microstructures. The hardness of lath bainite (LB), granular bainite (GB) and acicular ferrite (AF) is 8.0 GPa, 5.8 GPa and 3.0 GPa, respectively. The Charpy impact energy of weld metal with triple-wire welding procedure (136-165 J) is much greater than that with single-wire welding procedure (15-44 J) at − 45 °C. Larger cleavage facet size is observed in the fracture surface of single-wire weld metal. A computational procedure is developed to understand the temperature fields during the triple-wire welding. Combining the experiments and numerical simulation, simple models to predict the microstructure evolution through the weld thickness are established.

Characteristic Dependency of Hydrogen-Affected Fatigue Crack Growth and Crack Tip Plasticity on Low Loading Frequency in α-Iron

Aiming to investigate the dependency of hydrogen-affected fatigue crack growth (HAFCG) on the loading frequency f, this study experimentally characterized the HAFCG in a commercially pure iron as a function of f ranging from 0.02 to 20 Hz as well as a stress intensity factor range ΔK and hydrogen gas pressure $$ P_{{{\text{H}}_{2} }} $$ . The crack tip plasticity was analyzed by interferometric microscopy and transmission electron microscopy in addition to the fracture surface observation. As a result, the amount of FCG rate acceleration by hydrogen increases as f decreases until it reaches a critical value (f = 2 Hz at $$ P_{{{\text{H}}_{2} }} $$ = 3.5 MPa, f = 0.2 Hz at $$ P_{{{\text{H}}_{2} }} $$ = 35 MPa), while the HAFCG rate greatly decreases once f decreases below the critical value. At the same time, the fracture mode at $$ P_{{{\text{H}}_{2} }} $$ = 3.5 MPa changes from brittle quasi-cleavage to a more ductile manner showing no clear hydrogen influence. On the other hand, the size of cleavage-like facets becomes large in case of $$ P_{{{\text{H}}_{2} }} $$ = 35 MPa suggesting that the number of lattice planes causing cleavage is reduced because of less hydrogen effect. The crack tip plasticity reduction by hydrogen is clearly confirmed while the HAFCG enhancement occurs above the critical value of f. In contrast, at f below the critical value, the crack tip plasticity is recovered to almost the same level as in the inert environment. Based on a theoretical estimation of hydrogen diffusion from the crack tip, the critical value of f causing this reversal f dependency is likely determined by the hydrogen concentration gradient in the vicinity of the crack tip. Although the associated mechanism is still unclear, it is suggested that the dynamic interaction between mobile dislocations and diffusing hydrogen atoms is important in clarifying the mechanism of HAFCG.

Species and sex differences in eye morphometry and visual responsivity of two crepuscular sweat bee species (Megaloptaspp., Hymenoptera: Halictidae)

AbstractVisually dependent dim-light foraging has evolved repeatedly, broadening the ecological niches of some species. Many dim-light foraging lineages evolved from diurnal ancestors, requiring immense visual sensitivity increases to compensate for light levels a billion times dimmer than daylight. Some taxa, such as bees, are anatomically constrained by apposition compound eyes, which function well in daylight but not in starlight. Even with this constraint, the bee genus Megalopta has incredibly sensitive eyes, foraging in light levels up to nine orders of magnitude dimmer than diurnal relatives. Despite many behavioural studies, variation in visual sensitivity and eye morphometry has not been investigated within and across Megalopta species. Here we quantify external eye morphology (corneal area and facet size) for sympatric species of Megalopta, M. genalis and M. amoena, which forage during twilight. We use electroretinograms to show that males, despite being smaller than females, have equivalent visual sensitivity and increased retinal responsivity. Although males have relatively larger eyes compared with females, corneal area and facet size were not correlated with retinal responsivity, suggesting that males have additional non-morphological adaptations to increase retinal responsiveness. These findings provide the foundation for future work into the neural and physiological mechanisms that interface with morphology to influence visual sensitivity, with implications for understanding niche exploitation.

Photo-printing of faceted DNA patchy particles

Patchy particles with shape complementarity can serve as building blocks for assembling colloidal superstructures. Alternatively, encoding information on patches using DNA can direct assembly into a variety of crystalline or other preprogrammed structures. Here, we present a tool where DNA is used both to engineer shape and to encode information on colloidal particles. Two reactive oil emulsions with different but complementary DNA (cDNA) brushes are assembled into CsCl-like crystalline lattices. The DNA brushes are recruited to and ultimately localized at the junctions between neighboring droplets, which gives rise to DNA-encoded faceted patches. The emulsions are then solidified by ultraviolet (UV) polymerization, producing faceted patchy particles. The facet size and DNA distribution are determined by the balance between the DNA binding energy and the elastic deformation energy of droplets. This method leads to a variety of new patchy particles with directional interactions in scalable quantities.

Evidence for an elongated Achilles tendon in Australopithecus.

Modern humans have the longest Achilles tendon (AT) of all the living primates. It has been proposed that this anatomy increases locomotor efficiency and that its elongation may have played a crucial role in the origin and early evolution of the genus Homo. Unfortunately, determining the length of the AT in extinct hominins has been difficult as tendons do not fossilize. Several methods have been proposed for estimating the length of the AT from calcaneal morphology, but the results have been inconclusive. This study tested the relationship between the area of the superior calcaneal facet and AT length in extant primates. The superior facet is instructive because it anchors the retrocalcaneal bursa, a soft tissue structure which helps to reduce friction between the AT and the calcaneus. Calcanei from 145 extant anthropoid primates from 12 genera were photographed in posterior view and the relative superior facet size quantified. AT lengths were obtained from published sources. The relative area of the superior facet is predictive of AT length in primates (R2 = 0.83; p < .001) and differs significantly between the great apes and humans (p < 0.001). When applied to fossil Australopithecus calcanei, our results suggest that australopiths possessed a longer, more human-like, AT than previously thought. These findings have important implications for the locomotor capabilities of Australopithecus, including their capacity for endurance running and climbing.

Tensile properties, strain rate sensitivity and failure mechanism of single crystal superalloys CMSX-4

The tensile behavior of single crystal superalloys CMSX-4 was investigated under different strain rates at room temperature. The objective of this study is to identify the strain rate sensitivity and understand the damage failure mechanism by checking stress-strain curves and microstructure of the deformed sample. Experimental results show that the stress-strain curves including strain hardening behavior at both strain rates are different. The size of cleavage facets and dimples in the tensile fracture surface is related to the strain rates. The shearing lines cross through the γ matrix and γ' precipitates, which is related to the movement of dislocations. Then, Schmid factor and the damage failure mechanism during tensile tests are estimated and discussed.

Technical Note: Correction of geometric x-ray image intensifier distortion based on digital image correlation.

X-ray image intensifiers (XRIIs) inevitably produce images suffering from geometric distortion. Presently, various local and global methods exist to correct for these distortions. However, the performance of global methods is limited for dominant local distortions, and local methods tend to suffer from patch discontinuity and are generally sensitive to noise. In this paper, a novel local method is presented based on digital image correlation (DIC), which does not suffer from patch discontinuity and noise. As DIC is a very accurate and robust technique to analyze deformations, it is our candidate of choice to outperform the existing correction methods. The performance of our technique was first validated through distortion simulations. Next, it was validated experimentally for four different orientations of the XRII. A theoretical study on images suffering from a simulated distortion (including noise and blurring) yielded corrections with an average accuracy of (0.20±0.04) pixels. We obtained experimental data with our 14" XRII (292mm field of view), suffering from a maximum distortion between 9.6 and 12.9mm, and an average distortion between (4.4±1.3)mm and (6.1±2.5)mm over the image field for the different orientations. For an adequate choice of the facet size in the DIC analysis (greater than 40 pixels), the weighted mean residual error of our method varied between (0.037±0.003)mm and (0.054±0.003)mm, regardless of the XRII orientation. The maximum residual error varied between 0.081 and 0.185mm. From the simulations, we concluded that the proposed technique is affected by neither Gaussian noise nor blurring. Furthermore, it is shown that our method can reach an accuracy that is on par with or better than the current standard tools. The novel method is fast, requires minimal operator intervention and can be fully automated.

Modeling Polycrystalline Electrode-electrolyte Interfaces: The Differential Capacitance

We present and analyze a model for polycrystalline electrode surfaces based on an improved continuum model that takes finite ion size and solvation into account. The numerical simulation of finite size facet patterns allows to study two limiting cases: While for facet size diameter we get the typical capacitance of a spatially homogeneous but possible amorphous or liquid surface, in the limit , an ensemble of non-interacting single crystal surfaces is approached. Already for moderate size of the facet diameters, the capacitance is remarkably well approximated by the classical approach of adding the single crystal capacities of the contributing facets weighted by their respective surface fraction. As a consequence, the potential of zero charge is not necessarily attained at a local minimum of capacitance, but might be located at a local capacitance maximum instead. Moreover, the results show that surface roughness can be accurately taken into account by multiplication of the ideally flat polycrystalline surface capacitance with a single factor. In particular, we find that the influence of the actual geometry of the facet pattern in negligible and our theory opens the way to a stochastic description of complex real polycrystal surfaces.

A Multi-Barrier Model Assisted CAFE Method for Predicting Ductile-to-Brittle Transition with Application to a Low-Carbon Ultrahigh-Strength Steel

The conventional micromechanical approaches today are still not able to properly predict the ductile-to-brittle transition (DBT) of steels because of their inability to consider the co-operating ductile fracture and cleavage mechanisms in the transition region, and simultaneously to incorporate the inherent complexity of microstructures. In this study, a complete methodology with coupled cellular automata finite element method (CAFE) and multi-barrier microcrack propagation models is presented to advance the prediction of DBT. The methodology contains three key elements: (i) a multiscale CAFE modelling approach to realize the competition between ductile damage and cleavage fracture and embrace the statistical nature of microstructures, (ii) a continuum approach to estimate the effective surface energy for a microcrack to penetrate over particle/matrix interface, and (iii) a method to calculate the effective surface energy for the microcrack to propagate across grain boundaries. The prediction of DBT therefore needs only (1) the stress-strain curves tested at different temperatures, (2) the activation energy for DBT, (3) the ratio between the size of cleavage facets and cleavage-initiating defects, and (4) key statistical distributions of the given microstructures. The proposed methodology can accurately reproduce the experimental DBT curve of a low-carbon ultrahigh-strength steel.

Multiscale microstructural evolution in cold drawn pearlitic steel: A Palimpsestus Approach and a Tribute to Raffaello

This paper offers a palimpsestus approach to the multiscale microstructural evolution in progressively cold drawn pearlitic steel, analyzing in particular the evolution with cold drawing of: (i) the prior austenitic grain (zero, or virtual, microstructural level); (ii) the pearlitic colony (first microstructural level); (iii) the pearlite lamellae (second microstructural level). Results demonstrate that the slender pearlitic colony (after cold drawing) –more than the prior austenitic grain (that is also virtually cold drawn in the palimpsestus approach)– is the microstructural unit governing the cleavage facet size.

Texture-evolution of copper-based nanocatalyst via hybrid glow discharge plasma-oxalate-precipitation method for hydrogen production from CH3OH/H2O mixture

Hydrothermal, gel oxalate precipitation and non-thermal glow discharge plasma synthesis methods are used for preparation of CuO/ZnO/Al2O3 mixed oxide catalysts. The XRD analysis reveals that the lowest relative crystallinity and crystallite size of different crystallite facets are obtained for CZA-OG-P sample which has been synthesized via hybrid glow discharge plasma-oxalate-precipitation method. The FESEM and TEM analyzes prove that CZA-OG-P nanocatalyst possesses the tiniest particles size, the lowermost aggregation of particles, the most homogenous distribution of particles among all three synthesized samples. Assessment of different samples in steam reforming of methanol shows that CZA-OG-P has the highest methanol conversion and the lowest carbon monoxide production. Also, with the evaluation of the performance of CZA-OG-P sample for long duration use, it is determined that the value of methanol conversion and selectivity of this sample are almost stable. Eventually, deactivation study of the CZA-OG-P used sample is studied through TG/DTG and SEM-EDX analysis.

Slotted waveguide antenna with central trapped wave effect

ABSTRACTA new slotted waveguide antenna is proposed in this paper, which opens eight parallel slots along the longitudinal axis at the broad wall of the waveguide as radiation output facets. It has compact slot structure, which greatly reduces the size of the antenna, and the overall longitudinal size of the parallel slot facet is merely 3.8 mm (just slightly larger than half of the operating wavelength). The slot linear array design of the antenna achieves the central trapped wave radiation effect, avoids energy consumption at communication discontinuous zone, and enhances radiation efficiency. The operating bandwidth could be up to 10 GHz, with the center frequency of 85 GHz. The measured results match well with simulated results, and the gain is slightly higher than 9.0 dBi within the whole operating frequency range. The antenna has features of compact longitudinal structure, wide frequency band, stable gain, etc., and will have good application prospects in wireless communication.

Morphological and Biomechanical Implications of Cuboid Facet of the Navicular Bone in the Gait

The cuboid facet of the navicular bone is an irregular flat surface, present in non-human primates and some human ancestors. In modern humans, it is not always present and it is described as an “occasional finding”. To date, there is not enough data about its incidence in ancient and contemporary populations, nor a biomechanical explanation about its presence or absence. The aim of the study was to evaluate the presence of the cuboid facet in ancient and recent populations, its relationship with the dimensions of the midtarsal bones and its role in the biomechanics of the gait. 354 pairs of naviculars and other tarsal bones from historical and contemporary populations from Catalonia, Spain, have been studied. We used nine measurements applied to the talus, navicular, and cuboid to check its relationship with facet presence. To analyze biomechanical parameters of the facet, X-ray cinematography was used in living patients. The results showed that about 50 % of individuals developed this surface without differences about sex or series. We also observed larger sagittal lengths of the talar facet (LSAGTAL) in navicular bones with cuboid facet. No significant differences were found in the bones contact during any of the phases of the gait. After revising its presence in hominins and non-human primates, and its implication in the bipedalism and modern gait, we suggest that cuboid facet might be related with the size of talar facet and the position of the talonavicular joint. However, other factors such as geographical conditions, genetics and stressful activities probably affect its presence too.

Neither lateral patellar facet nor patellar size are altered in patellofemoral unstable patients: a comparative magnetic resonance imaging analysis

It remains unclear if morphologic patterns of the patella itself predispose to patellar instability. This study examined established patellar landmarks in relation to the femoral condyle width to clarify differences of patellar morphologies in patellofemoral stable and unstable patients. Magnetic Resonance Imaging of 50 subjects (20.7 ± 4.4years; 17 males, 33 females) with patellofemoral instability (study group, SG) and 50 subjects (25.3 ± 5.8years; 31 males, 19 females) with anterior cruciate ligament rupture (control group, CG) were analyzed. Corresponding patellar value indices (PW-I; LPF-I 1; LPF-I 2) in relation to the femoral condyle width (FCW) were evaluated after the measurement of absolute patellar dimension [patellar width (PW); direct length of the lateral patellar facet (LPF-1); projected length of the lateral patellar facet (LPF-2)]. The patellar shape according to Wiberg, trochlear dysplasia, patellar height, and tibial tubercle-trochlear groove (TT-TG) distance were determined. The SG showed a significantly longer absolute (LPF 2) (P = 0.041) and relative (LPF-I 1, LPF-I 2) (P < 0.001) lateral facet of the patella. No significant differences were evaluable for the relative patellar width (PW-I) (ns). A patellar shape type 3 (P = 0.001) as well as a higher position of the patella and TT-TG-distance (P < 0.001) were significantly more often present in the SG. There are several bony alterations associated with patellofemoral instability, but our data did not show a significantly smaller lateral patellar facet or relative patellar width that could facilitate a patellar dislocation. This helps surgeons, that are considering to surgically address the patella in cases of patellofemoral instability, to better understand its morphologic pattern. III.

Improvement of Mechanical Properties of Zr-Based Bulk Amorphous Alloys by High Temperature Heat Treatment

Zr-based bulk amorphous alloys which were heat-treated from 673 to 1073 K were investigated, and compressive fracture mechanisms related with improvement of mechanical properties were investigated by observing how the type, size and volume fraction of crystalline particles which is generated during the heat treatment affected the fracture mode. The Zr-based bulk amorphous alloys contained nano-sized crystalline particles showed excellent mechanical properties of compressive fracture strength over 2.0 GPa and compressive plastic strain of approximately 1%. The fracture modes of the alloys are changed depending on the heat treatment temperature and their microstructure. When the alloy is heat-treated at 673 K, the nano-sized Zr2Cu particles are generated in amorphous matrix. According to the observation of fractured specimens, in the alloy heat-treated at 673 K, the fine and elongated vein patterns were well developed. The heat treatment temperature increased above Tx, the Zr2Cu particles as well as complex crystalline particles are consist in the heat-treated alloy, which lead to the brittle fracture and the alloy show the low strength of 605 MPa. In the fractured surface of the alloy, large cleavage facets were evenly developed. When the heat treatment temperature up near Tm, the size of Zr2Cu and complex crystalline particles increased to approximately 1 μm and the volume fraction of complex crystalline particles increased up to 52.3%. As the size of crystalline particles change, the size of facet decreased similarly to the size of crystalline particles. Zr-based bulk amorphous alloys which were heat-treated from 673 to 1073 K were investigated, and compressive fracture mechanisms related with improvement of mechanical properties were investigated by observing how the type and size of crystalline particles which is generated during the heat treatment affected the fracture mode. The fracture modes of the alloys are changed depending on the heat treatment temperature and their microstructure. When the alloy is heattreated at 673 K, the nano-sized Zr2Cu particles are generated in amorphous matrix. According to the observation of fractured specimens, in the alloy heat-treated at 673 K, the fine and elongated vein patterns were well developed. The heat treatment temperature increased near Tg, the Zr2Cu particles as well as complex crystalline particles are consist in the heat-treated alloy, which lead to the brittle fracture and the alloy show the low strength of 605 MPa. In the fractured surface of the alloy, large cleavage facets were evenly developed. When the heat treatment temperature up near Tm, the size of Zr2Cu and complex crystalline particles increased to approximately 1 μm.

Determination of Stress Intensity Factors and J integral based on Digital Image Correlation

Digital image correlation (DIC) is a technique in experimental mechanics to acquire full-field measurement data of displacements and deformations from the surface of specimens or components. Especially for the investigations of cracks it provides additional benefits. The actually present deformation field in the vicinity of the crack tip can be obtained which directly reflects for example crack closure effects or plasticity. Against this background the paper summarizes a procedure to compute the J integral and the stress intensity factors KI and KII based on DIC data. For this purpose the J and interaction integral are computed as line and domain integrals. Through experiments it is shown that the domain integral is less affected by scatter of the DIC data. Furthermore, the specific domain, facet sizes and facet distances slightly influence the results.