Initial Zone Research Articles

Dynamice fracture in a semicristalline polymer: an analysis of the fracture surface

The fracture behaviour of a specific material, a semi-crystalline biobased polymer, was here studied. Dynamic fracture tests on strip band specimens were carried out. Fracture surfaces were observed at different scales by optical and electron microscopy to describe cracking scenarios. Crack initiation, propagation and arrest zones were described. Three distinct zones are highlighted in the initiation and propagation zone: a zone with conical markings, a mist zone and a hackle zone. The conical mark zone shows a variation in the size and density of the conical marks along the propagation path. This is synonymous with local speed variation. Microcracks at the origin of the conical marks in the initiation zone seem to develop from the nucleus of the spherulites. In the propagation zone with complex roughness, the direction of the microcracks and their cracking planes are highly variable. Their propagation directions are disturbed by the heterogeneities of the material. They branch or bifurcate at the level of the spherulites. In the arrest zone, the microcracks developed upstream continue to propagate in different directions. The surface created is increasingly smoother as the energy release rate decreases. It is shown that the local velocity of the crack varies in contrast to the macroscopic speed.

Post‐landslide soil and vegetation recovery in a dry, montane system is slow and patchy

AbstractLandslides are common disturbances in forests around the world, and a major threat to human life and property. Landslides are likely to become more common in many areas as storms intensify. Forest vegetation can improve hillslope stability via long, deep rooting across and through failure planes. In the U.S. Rocky Mountains, landslides are infrequent but widespread when they do occur. They are also extremely understudied, with little known about the basic vegetation recovery processes and rates of establishment which restabilize hills. This study presents the first evaluation of post‐landslide vegetation recovery on forested landslides in the southern Rocky Mountains. Six years after a major landslide event, the surveyed sites have very little regeneration in initiation zones, even when controlling for soil coverage. Soils are shallower and less nitrogen rich in initiation zones as well. Rooting depth was similar between functional groups regardless of position on the slide, but deep‐rooting trees are much less common in initiation zones. A lack of post‐disturbance tree regeneration in these lower elevation, warm/dry settings, common across a variety of disturbance types, suggests that complete tree restabilization of these hillslopes is likely to be a slow or non‐existent, especially as the climate warms. Replacement by grasses would protect against shallow instabilities but not the deeper mass movement events which threaten life and property.

Detonation Parameters of Mixtures Produced by Injecting Gaseous Components into the Barrel of a Pulse Gas Detonation Installation

A CCDS2000 detonator for acetylene, ethylene, propylene, and a multicomponent methylacetylene–allene fraction (MAF) fuel is used to perform experiments on measuring the detonation velocity and recording a detonation front cell in a tube 26 mm in diameter and 2 m in length. The experiments are carried out at atmospheric pressure in stoichiometric mixtures diluted by nitrogen to air concentrations and in air–fuel mixtures with a varying fuel content in them. In the case where the explosive mixture components are fed as a flow by stratifying an explosive charge in an initiation zone, a self-sustaining detonation is stably ignited up to limiting (spin) modes. The concentration limits of the detonation existence are determined. In the air–fuel mixtures of acetylene and ethylene, as the values become lower than the limits, there is multiheaded detonation. For propylene and MAF, a tube diameter of 26 mm is near-critical: only single- and two-headed spin is observed in the entire range of existence. Calculation results are in good agreement with the experiment.

Temporal variability in gametogenesis and spawning patterns of crown-of-thorns starfish within the outbreak initiation zone in the northern Great Barrier Reef

Population outbreaks of the coral-eating crown-of-thorns starfish (CoTS) have resulted in extensive coral mortality on reefs in the Indo-Pacific region and is considered one of the major contributors of significant declines in coral cover in Australia’s Great Barrier Reef (GBR). Effective management of CoTS outbreaks rely on improved understanding of the drivers of individual and population-level differences in reproductive patterns, particularly those factors that may contribute to step-changes in reproductive success, such as the timing and synchronicity of spawning. This study investigated gametogenesis and spawning patterns in a persistent population of CoTS at one reef within the putative initiation zone where outbreaks appear to start in the GBR. We examined variation in the progression of gametogenesis and spawning patterns over two distinct spawning seasons (2013–2014, 2014–2015), using a variety of methods: macroscopic examination of gonads, assessment of monthly changes in the gonadosomatic index, analysis of histological sections of ovaries and testes, and comparison of the size-frequency distribution of oocytes. These methods yielded consistent results, which revealed striking variation in the timing of maturation and gamete release between two summer spawning seasons, possibly depending on local environmental conditions. The optimal temperature for gametogenesis and spawning occurred when seawater temperature exceeded 28 ℃. Gradual increases in temperature (to > 28 ℃) over spawning months in 2013–2014 caused ‘batch/dribble’ spawning, while abrupt increases in temperature in 2014–2015 caused synchronous ‘all-at-once’ spawning. During more rapid warming events in the typical summer spawning period, CoTS may exhibit greater synchronicity in their reproductive capacity, which may help seed outbreaks. This work advances our understanding of the mechanisms surrounding periodic fluctuations in CoTS densities and improves predictions on how this corallivorous predator will respond to environmental perturbations due to climate change.

Variation in rainfall patterns triggering debris flow in the initiation zone of the Ichino-sawa torrent, Ohya landslide, Japan

Rainfall patterns that trigger debris flows may vary depending on the amount of sediment storage in their initiation zones. However, the current literature did not fully explore the relationship between the rainfall patterns triggering debris flows and changes in sediment storage. In this study, we investigated the variation in rainfall patterns for debris-flow occurrences via field-based, four-year monitoring in a steep mountainous torrent (the Ichino-sawa torrent) in Japan. In this catchment, the sediment storage changes seasonally owing to the sediment discharge by debris flow from summer to fall and sediment recharge due to freeze–thaw cycles during winter. We found that the readily mobilized sediment was locally accumulated in response to rainfall above the 5-mm 10-min−1 threshold. Subsequent debris-flow surges caused the entrainment of the accumulated sediment, which led to their development and propagation. Accordingly, the rainfall patterns that triggered debris flow tended to include longer consecutive periods above the rainfall threshold compared with the rainfall patterns that did not trigger debris flow. However, the decrease in sediment storage due to previous debris-flow events reduced the period above the threshold required to trigger debris flows. Hence, the decrease in sediment storage during summer to fall seasons reduced the rainfall threshold for debris-flow occurrences. Conversely, after sediment recharge during the subsequent winter, a relatively long period above the rainfall threshold was again necessary for debris-flow occurrences. Therefore, the rainfall pattern that triggers debris flow varies in response to the cycle of sediment discharge and recharge.

Exploring the hydromorphological response to human pressure in Tagus River (1946–2014) by complementary diagnosis

Different levels of human pressures have modified the dynamism and the morphological pattern of most riparian environments worldwide. Among the anthropogenic agents, flow regulation by dams, gravel mining; artificial land use and land cover changes together with climate change are the most frequently studied. Medium and short term geomorphological adjustments and riparian vegetation cover changes have been frequently studied by using a variety of methodological approaches, with the diachronic analysis of orthophotographs as the most common starting point. The main objective of this research is to assess the spatio-temporal evolution of geomorphological conditions and riparian vegetation cover along a 38 km-long reach of the Tagus River, analysing the last 70 years, in order to understand the main drivers leading to those changes. To that purpose, a complementary diagnosis has been carried out by combining different approaches: (1) Simple geomorphological indicators, (2) Specific geomorphic indexes, (3) Landscape metrics and (4) Transition matrices, together with the analysis of flow discharges. Results show that River Tagus has suffered a narrowing process (67.7%) along the entire study period (1946–2014) close to a decrease in width ratio of 2.1 m/year. However, the narrowing trend was not stable along the entire period, with the most dramatic reduction happened between 1956 and 1975 with a decrease ratio around 7.1 m/year for that subperiod. At the same time, woody riparian vegetation, grass and shrubs covers decreased in comparison with 1946 photo while agriculture land increased within initial riparian zone. By combining different approaches, we note the progressive impoverishment of geomorphic status that is more severe when we consider the area (-49%) of fluvial landforms instead of their number (-26%), in parallel with the fragmentation and complexity pattern found for both vegetated and bare gravel bars according to landscape patchiness analysis. Our results show that geomorphic status in the 4 sub-reaches have decreased, although in the case of sub-reach 1 and 4 the response presents a delay with the more important decrease occurring from 1975 to 1999. This geomorphological evolution is explained by the synergic combination of different human pressures along time. Initially, flow regulation by large dams influenced this evolution, but water-transfer since 1979 and floodplain occupation by farmland activities were more relevant with the time. River dynamism, figured out as the amount of area subject to rejuvenation (i.e., evolution toward more pioneer stages) and succession processes (i.e., evolution toward more mature stages), was reduced more than a half along the period 1946–1975, while it completely changed after 1975 where they became close to 10% of the initial dynamism. Thus, our results show by the combination of different approaches that River Tagus channel has become immobilized, reduced with a simplified morphology and its riparian vegetation lost its dynamism converted into a mature wood.

Quantitative analysis on the surface topography of Ti-6Al-4V machined by abrasive suspension jet

Surface topography is the intrinsic determinant of the roughness that is a significant evaluation standard for the machining quality of the abrasive suspension jet (ASJ). To achieve quantitative analysis on the surface topography machined by ASJ, this paper measured the roughness and the scratch size of the cutting surface with an ultra-deep three-dimensional microscope. Ti-6Al-4V (TC4), a typical hard machining material widely used in aviation industry, was chosen as the cutting target. From a macroperspective, the cutting surface is divided into four zones from top to bottom including the initial zone, the smooth zone, the transition zone, and the rough zone. With 1.6-μm set as the standard roughness, the length of the initial zones and the smooth zone were analyzed and determined. From a microperspective, there are a large number of particle scratches with micron scale size laid on the cutting surface. The experimental results showed that the length of the scratches in the initial zone was less than the one in the smooth zone, while it was opposite in the scratch depth and width, and that the initial zone is larger than the smooth zone in surface roughness could be explained. The abrasive particle size is the only influent parameters of the scratch size, and small abrasive particles can be used for reducing the roughness in the initial zone and smooth zone. The conclusions can provide theory guidance for abrasive water jet processing titanium alloys precisely.

Corrosion study on low molecular organic acids in the initial condensation zone of steam turbines

Purpose The purpose of this study was to investigate the corrosion of low molecular organic acids from water-steam cycles such as acetic acid and formic acid in mental parts of steam turbine initial condensation zone. Design/methodology/approach The corrosion behavior of gray cast iron in initial condensate containing different concentrations of acetic acid and formic acid was studied by weight loss test, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Findings The results indicated that gray cast iron had a certain degree of corrosion in the simulated initial condensate containing acetic acid and formic acid, but the acid corrosion of gray cast iron was not only caused by low molecular organic acid but also affected by inorganic anions such as Cl−. When Cl− existed, after removing corrosion products, surface analysis results proved that the surface of gray cast iron was rough and uneven with many cracks, which was corrected more serious. Originality/value The corrosion behavior of thermal equipment by low molecular organic acids and inorganic anions in water-steam cycles was studied. The research results can provide theoretical guidelines for corrosion control of steam turbine in power plants.

Elastic–plastic problem for a circular hole plate with regard to crack initiation in elastic zone

A plane elastic–plastic problem of stress distribution in a circular hole thin plate involving initiation and propagation of cracks in an elastic zone, is considered. It is assumed that the stress level is such that the circular hole is entirely enclosed by the plastic deformations zone. The plate material satisfies the Tresca–Saint Venant plasticity condition. It is supposed that cracks initiation and fracture of the plate material occur in the loading process in the elastic zone. Location and size of prefracture zone in the plate material are unknown in advance and are to be determined. The methods of theory of perturbations and theory of singular integral equations are used. As a crack appearance condition, we use the criterion of critical opening of prefracture zone faces. The interface of elastic and plastic deformations and also the location and sizes of crack initiation zones are found.

Coupled damage variable based on fracture locus: Prediction of ductile failure in a complex structure

This article focuses on predicting the instant of failure in a real scale component of complex geometry and loading using a ductile damage model calibrated exclusively on small-scale laboratory specimens of relatively simple shape. The ductile behaviour of a strain hardened aluminium alloy AA1050, formed into a thin-walled component, is modelled by a coupled ductile fracture locus model presented in a recent study (Baltic et al., 2020). The component is exposed to high internal pressure and has a safety vent designed for safe pressure handling. The extensive plastic deformation in the safety vent leads to localised ductile failure occurring at a limit load. The pertaining material parameters were calibrated solely from basic ductile fracture experiments in the preceding work (Baltic et al., 2020), where the bottom section of the thin-walled component was machined into notched and shear samples to characterize different states of stress and to construct a well-defined fracture locus. Although the calibrated material model relies on the local fracture strain measurements, it involves a regularization as a function of the length scale defined as a width of the observed localisation band from Digital Image Correlation (DIC) analysis. In the current study the calibration on small-scale specimens is complemented by a large-scale specimen to determine the length scale correction crucial for capturing the correct width of the localisation band in the analysed structure. This is necessary because the failure initiation zones of the calibration specimens and the real size structure, i.e. their gauge lengths where the localisation band appears, vastly differ in size. Finite element (FE) model results are compared to measurements of the deformation of the aluminium component under pressure and maximum load prior to failure. The numerical and experimental results show an excellent agreement and consistent fracture predictions for various mesh discretizations.

The Neoarchean GT-34 Ni deposit, Carajás mineral Province, Brazil: An atypical IOCG-related Ni sulfide mineralization

The GT-34 deposit, located 12 km to the SW of the Sossego copper–gold mine in the Carajás Province, northern Brazil, represents an unusual Ni sulfide mineralization. The deposit occurs along a NE-SW-trending sub-vertical shear zone marked by progressive Mg-alkalic alteration zones, predominantly hosted in granitic and locally in granodioritic to tonalitic orthogneisses. Initial alteration zones result in unique scapolite-orthopyroxene assemblage, which is partially preserved within pervasive hornblende-chlorapatite ± plagioclase replacement zones. Nickel mineralization occurs mainly as matrix-supported breccias characterized by a pentlandite-pyrrhotite-rich matrix and rounded fragments chiefly of hornblende and chlorapatite. Irregular stockworks and net textured veins containing chalcopyrite-pentlandite are less common. Phlogopite ± talc ± actinolite alteration and late-stage veinlets crosscut the previous alteration zones and the mineralization. The phlogopite ± talc ± actinolite alteration occurs as irregular veins and chalcopyrite-pyrrhotite-magnetite are commonly observed where such alteration intersects the Ni mineralization. Late-stage veinlets are represented by K feldspar-epidote-chlorite-calcite and quartz-albite-chlorite-calcite-epidote veins, both containing minor amounts of millerite, pyrite and F-OH-apatite. High-resolution SIMS U-Pb zircon geochronology obtained for the GT-34 deposit revealed an age of 2828 ± 4 Ma for zircon grains inherited from the host orthogneisses. The timing of the mineralization altered zircon grains from the scapolite-orthopyroxene and phlogopite ± talc ± actinolite alteration zones, is attributed to an age interval between 2751 and 2720 Ma. Although poorly constrained, the geochronological data corroborate a Neoarchean age for the GT-34 Ni mineralization, similar to that of other IOCG deposits in the Carajás Province and coeval with the bimodal magmatism in the area. The atypical orthopyroxene-marialite mineral chemistry support a metasomatic crystallization at high temperatures (>700 °C), low aH2O (<0.5) and pressures between 5 and 7 kbar. Hypersaline fluids, as the ones described for the IOCG deposits in Carajás at such PxT conditions, would enable the orthopyroxene-marialite crystallization, as supported by experimental studies available in the literature. Mineralogical and geochemical considerations on the nature of the Ni sulfide mineralization points toward a metasomatic origin, feasible with the predicted P-T-fluid scenario for the hydrothermal alteration. Such conditions raise the initial temperature and pressure estimates of the IOCG metasomatic alteration by at least 200 °C and pressure up to 7 kbar, making it the hottest and probably deepest IOCG-related metasomatic alteration known to date for Carajás.

The Effect of Dissolved Cavern on the Fracture Propagation in Vuggy Carbonate Reservoir

Abstract The acid-fracturing is applied wildly to simulate the formation in vuggy carbonate reservoirs. But it does not figure out clearly the mechanism of fracture propagation while fracture encountering dissolved cavern, and there are few researches considering the influence of dissolved cavern on fracture propagation. In order to study fracture propagation regularity in vuggy carbonate reservoirs, numerical simulations are carried out by the seepage–stress–damage coupling equation based on the damage mechanics theory and the accuracy of the model is validated by comparison with experimental results. Some factors influencing the fracture propagation such as dissolved cavern, formation parameters, and construction parameters are considered. The simulation results show that there are four fracture propagation forms after the fracture encountering dissolved cavern, namely, block, crossing over directly, crossing over after deflection, and deflection. The entire process of injecting the pressure curve can be divided into five stages: initial initiation zone, encountering dissolved cavern pressure released zone, the dissolved cavern inside builds the pressure zone, re-ruptured zone, and fracture propagation zone. The horizontal principal stress difference of the formation controls the tendency of fracture propagation and the generation of branch fractures. It is easy to generate branch fractures under the condition of low horizontal principal stress. The increase in horizontal principal stress limits the deformation of fracture, making it more convenient for fracture to extend toward the maximum horizontal principal stress. The study results are significant for optimizing fracturing construction plans and improving the probability of connection between fracture and dissolved cavern.

Collision probability between intruding drone and commercial aircraft in airport restricted area based on collision-course trajectory planning

With the significant improvements in drone technology and the popularization of drones among their hobbyists, the incidents of drones intruding airports have resulted in a large number of flight delays and temporary closure of runways. To minimize the interference of drones on normal operations in the airports, a collision probability evaluation scheme based on collision-course trajectories modeling is proposed in this work. Firstly, a trajectory planning model of drones intruding restricted airspace is derived based on a given trajectory of the commercial aircraft (CA) and the collision-course scenario of the drone. Subsequently, according to the trajectories of the drone and CA, a probabilistic model based on the stochastic kinematic model is developed to implement the collision risk evaluation. The proposed method is first comparatively demonstrated with the Monte-Carlo (MC) simulation and several special cases with known drone’s trajectories. Subsequently, the cases covering different drone’s initial positions, positions updates, and different collision zones are simulated and analyzed using the proposed collision-course based model. The simulation results show that the established model can be employed to evaluate the collision probability, even if the trajectory information of the intruding drone is limited.

Miocene Subsidence and Surface Uplift of Southernmost Tibet Induced by Indian Subduction Dynamics

AbstractThe Indus‐Yarlung suture of southernmost Tibet marks the initial collisional zone, the ongoing India‐Asia collision, and yet more than ~30 million years after the onset of collision, a thick detrital sedimentary unit was deposited just north of the suture: the Kailas Formation. The mechanism permitting subsidence of the deep intracontinental Kailas basin in a compressional tectonic regime remains uncertain. We present new apatite (16–11 Ma) and zircon (24–19 Ma) fission track (AFT and ZFT) ages from the Gangdese batholith just north of the Kailas basin. ZFT analysis of modern‐river sand from the northern Gangdese magmatic arc indicates an exhumation at 27.3 ± 1.3 Ma. Thermal modeling indicates that the batholith experienced reheating between 28 and 20 Ma, coeval with deposition in the Kailas basin (between 26 and 21 Ma), followed by overall rapid cooling between 20 and 17 Ma. We interpret this thermal history as a phase of regional Oligocene‐Miocene sedimentary burial followed by exhumation. By modeling mantle dynamics in the geodynamic framework of the India‐Asia collision, we show that transient dynamic topography over the relative southward folding of the Indian slab is consistent with burial and exhumation of the Gangdese magmatic arc during Oligocene‐Miocene time. The northward migration of the Indian continent relative to its own stati onary slab created a wave of dynamic topography that caused subsidence in the overriding plate north of the Himalaya, followed by a phase of surface uplift since ~27 Ma of the northern Gangdese magmatic arc. During latest Oligocene‐early Miocene time, the dynamic deflection center was in the Kailas area, and it progressively relocated southward to its present position at the Ganges basin.

Magmatic Processes at the Oman Ophiolite Paleoridge – Perspectives on the Role of Water

AbstractThe Oman ophiolite is regarded as best proxy for accreted oceanic crust from typical fast‐spreading ridge systems on land. However, the Oman ophiolite is influenced by initial subduction zone initiation, and the nature of the details of the subduction zone setting is still under controversial debate. While a first magmatic phase shows features of magmatic accretion very similar to those known from the East Pacific Rise, except that the primary melts were slightly water‐enriched, a second type of magmatism is characterized by an apparent subduction‐zone related imprint, producing rocks like FAB basalts and boninites in the upper crust, as well as cross‐cutting gabbronorites and wehrlites in the deeper crust. In this paper, we apply diverse experimental studies in wet tholeiitic and peridotitic systems performed at lower pressures (100 to 500 MPa) in the experimental lab of the University Hannover, in order to constrain the details of the magmatic processes proceeded at the Oman ophiolite paleoridge during the Cretaceous, with special focus on the influence of water on the phase stabilities and phase relations. The experiments were performed in vertically oriented internally heated pressure vessels (IHPV) (see Berndt et al., 2002; Fig. 1). This facility uses as pressure medium mixtures of Ar and H2 in order to adjust the required fH2 in the vessel, enabling us to control the redox conditions. The fH2 prevailing in the IHPV at high P and T was measured with a Shaw‐membrane made of platinum. The overall variation in fO2 in all experimental series was in the range between ∼FMQ‐1 and ∼FMQ+3.2, thus covering the range of oxygen fugacities prevailing in natural MORB magmas (Bezos and Humler, 2005).For understanding the magmatic processes during the Oman ophiolite paleoridge accretion, transects through the lower (GT1) and middle (GT2) crust have been drilled in the frame of ICDP (International Continental Scientific Drilling Program). Drill sites have been selected in the Wadi Tayin massif, which is known that the influence of magmatic phase 2 characterized by subduction‐related primary melts is minimal. Details and progress obtained in the Oman Drilling Project (OmanDP) can be found here: (https://www.omandrilling.ac.uk/). Regarding the first magmatic phase of the processes at the Oman ophiolite paleoridge, a characteristic observation made during the description of the drilled cores GT1 (lower crust) and GT2 (mid‐curst) was that quite often layers in the layered gabbro series occur which show the presence of clinopyroxene joining olivine instead of plagioclase (under near liquidus conditions). In terms of lithologies this could be interpreted as presence of wehrlitic crystal mushes as early cumulates instead of troctolitic, which are the typical ones for primary magmatism at typical fast‐spreading ridges. This situation could be experimentally simulated by adding a moderate to high water activity to primitive MORB at pressures ≥ 200 MPa, resulting in a shift of the clinopyroxene‐in curve to higher temperatures above the plagioclase‐in curve (Feig et al. 2006; see Fig. 2).Regarding the second, late‐stage magmatic phase, the formation of typical Oman high‐Ca‐boninites could be experimentally simulated by water‐saturated partial melting of Oman harzburgite at 200 MPa and relatively low temperatures between 1100 and 1200°C. Depleted gabbronorites crosscutting layered gabbros of phase 1 magmatism can be regarded as cumulates formed in these boninitic melts. Late wehrlites crosscutting layered gabbro could be produced by accumulation of olivine and clinopyroxene at temperatures between 1040 and 1080°C in a hydrous gabbroic system at pressures &gt; 100 MPa with bulk water content of 2–3 wt%.

Numerical simulation of violent breaking wave impacts on a moored offshore wind turbine foundation over nonuniform topography

Breaking wave impact on a moored offshore wind turbine foundation over a variable-depth seabed is considered in time domain, based on the fully nonlinear potential theory. An adiabatic model is used to simulate the variation in air cavity volume and pressure imposed on the dynamic boundary condition of the inner free surface. The whole impact process is solved using the dual coordinate system, where a local stretched coordinate system is adopted to determine both the shape and location of the initial impact zone, while the global coordinate system is applied to track further development of both the upper and lower jets. A higher-order boundary element method is introduced to establish water integral equations of the main fluid domain and the thin jet, which are combined together with the match conditions of pressure and velocity on the interface. By employing auxiliary functions, the temporal derivative of velocity potential is accurately obtained to decouple the mutual dependence of body and fluid motions. A specified global coordinate-based finite element method is used to derive the dynamic equilibrium equation of the mooring line element. Through the hinged condition at the fairlead location, the motion equations of the wind turbine and its mooring system are simultaneously solved using the Newton–Raphson iterative method. Extensive simulations are performed and discussed for the free surface profile, pressure distribution, body motion, and air cavity features. The wind turbine moored at the seabed with larger slope was found to experience relatively higher air cavity pressure and achieve larger rotational speed, smaller horizontal, and vertical speed.

Fatigue life assessment in notched injection-molded specimens of a short-glass fiber reinforced Polyamide 6 with different injection gate locations

Based on a previously published Through Process Modeling (TPM) for multiaxial fatigue life assessment of injection-molded components, this work aimed to capture the difference of fiber orientation distribution ahead of notch tips in flat notched samples of PA6GF30 tested in tension at ambient temperature. The fiber orientation originated from different locations of the injection gate for an unchanged macroscopic geometry. Good lifetime estimations were obtained in Side- (resp. Top-) injected samples, regardless the choice of the sample type from which the fatigue criterion was identified. The experimentally observed differences of crack initiation zones were correlated to numerical simulations.

Generality of Starobinsky and Higgs inflation in the Jordan frame

We revisit the problem of generality of Starobinsky and Higgs inflation. The known results obtained in the Einstein frame are generalized for the case of an arbitrary initial energy of the scalar field. These results are compared with the results obtained directly in the Jordan frame, which, to our knowledge, has not been thoroughly explored in the literature previously. We demonstrate that the qualitative picture of initial conditions zone in the $(\phi, \dot \phi)$ plane, which leads to sufficient amount of inflation, is quite similar for both the frames in the case of Higgs inflation. For Starobinsky inflation, the conformal transformation between the frames relates the geometrical variables in the Jordan frame with the properties of an effective scalar field in the Einstein frame. We show that the transformation $(H, R) \to (\phi, \dot \phi)$ is not regular everywhere, leading to some peculiarities in the zone of good initial conditions in the $(H, R)$ plane.

Evolution of Mechanical Properties of Ti–6Al–4V Alloy in the Temperature Range of 20 to − 196 °C

Cryogenic cooling is becoming an attractive method for machining difficult-to-cut materials to extend their machinability. However, it’s a challenging task to analyze the effect of cryogenic cooling on the machining. In order to better understand the various physical phenomena in the cryogenic cutting process, cryogenic impact test, and tensile test of titanium alloy Ti–6Al–4V were undertaken in this work. The impact and tensile properties of Ti–6Al–4V alloy in the temperature range of 20 to − 196 °C were investigated. Later on, the macroscopic and microscopic morphology of the produced fractures were analyzed. Findings have depicted a decreasing impact toughness and an increase of tensile and yield strength of Ti–6Al–4V alloy in the temperature range from 20 to − 196 °C. The impact fracture appeared as a tendency of becoming material brittle. Meanwhile, three kinds of zones of shear-lip, fiber, and radiation were found on the fracture morphology. Those zones correspond to the shear fracture zone, crack initiation zone, and crack extension zone, respectively. With the temperature decrease, the proportion of fiber zone was decreased, while a gradual increase in the radiation zone was observed. Besides, the fiber zone was observed for the macroscopic morphology of the fracture under the temperature of − 196 °C. Some dimples were found in the tensile fracture at − 196 °C indicating the ability of Ti–6Al–4V alloy to deform plastically under such low temperature. This work is a fundamental support to analyze the behavior of Ti–6Al–4V alloy under cryogenic cooling conditions.

Dynamic fracture in a semicrystalline biobased polymer: an analysis of the fracture surface

The fracture behaviour of a semi-crystalline bio-based polymer was studied. Dynamic fracture tests on strip band specimens were carried out. Fracture surfaces were observed at different scales by optical and electron microscopy to describe cracking scenarios. Crack initiation, propagation and arrest zones were described. Three distinct zones are highlighted in the initiation and propagation zone: a zone with conical markings, a mist zone and a hackle zone. The conical mark zone shows a variation in the size and density of the conical marks along the propagation path. This is synonymous with local speed variation. Microcracks at the origin of the conical marks in the initiation zone seem to develop from the nucleus of the spherulites. In the propagation zone with complex roughness, the direction of the microcracks and their cracking planes are highly variable. Their propagation directions are disturbed by the heterogeneities of the material. They branch or bifurcate at the level of the spherulites. In the arrest zone, the microcracks developed upstream continue to propagate in different directions. The surface created is increasingly smoother as the energy release rate decreases. It is shown that the local velocity of the crack varies in contrast to the macroscopic speed. A specific setup allowing to estimate the minimum fracture energy of the material in order to maintain the rapid propagation of the crack is proposed for materials with antagonistic behaviour: ductile at initiation and brittle in propagation.