Fracture Point Research Articles

Effect of laser surface modification on the tensile properties of ultra-thin titanium sheet

Laser scanning irradiation (LSI) was a promising method to improve the surface hemo-compatibility of vascular stent (VS). This paper firstly studied the effect of LSI on the tensile properties of ultra-thin Ti sheet, the thickness of which was close to that of VS’s wall. Meanwhile, the influence of plastic deformation on the hydrophilicity of LSI sheets and the hydrophobicity of the ones modified with fluorosilane was evaluated. The results indicated that the tensile properties of Ti sheets gradually declined with increasing laser fluence (Fp) and decreasing scanning speed (v). As using laser gentle ablation (LGA) with Fp = 1.1 ∼ 2.9 J/cm2, the declination degree of tensile properties was relative slight, but it was obviously sharper as using laser strong ablation (LSA) with Fp = 4.0 ∼ 6.6 J/cm2. In addition, the tensile and yield strengths of LSA samples using v = 42 mm/s were much smaller than those using higher v of 126 ∼ 630 mm/s, owning to the much larger laser-ablated depth in the surfaces. All of the LSA surfaces exhibited superhydrophilicity, and after fluorination they rapidly turned to be superhydrophobic with low adhesion to water. Interestingly, plastic deformation within the tensile fracture point slightly improved the super-hydrophilicity or superhydrophobicity of these LSA surfaces rather than destroyed it. Therefore, LSA with v = 126 ∼ 630 mm/s was more suitable to be applied in the stent, which could not only obtain super-hydrophilicity/hydrophobic surfaces with hierarchical microtextures but just slightly affect the stent’s tensile properties.

마그네슘 합금 판재(AZ31B)의 인장 변형에서 AE 신호 발생 특성 분석

In this study, acoustic emission (AE) signals associated with the behavior of materials in the magnesium alloy (Mg AZ31B) tensile test were analyzed. The AE sensor was attached with the material to measure the AE signals. During the tensile experiment, the AE sensor measured the elastic waves generated inside the specimen. The AE parameters, such as, the signal energy, duration, and frequency centroid, were studied. We also analyzed the effect of the materials size and tensile speed on the AE signals. As a result, the lowest frequency centroid value occurred at the yield and fracture points. As the width and length of the specimen increased, the number of hit counts increased and the peak frequency occurred. Other AE parameters, such as, the duration and frequency centroid, were not affected. As the tensile speed increased, the hit decreased and the frequency centroid decreased in the elastic region. It was found that in the detection of the yield and fracture deformation, the number of counts, and frequency centroid were appropriate.

Uniaxial compression of dry wood: experiment and modeling

The paper considers the dependence of the load on displacement during uniaxial compression of spruce wood samples with an adjustable deformation rate (1 mm/min); the water content in the samples was equal to 6.4%. The study focuses on the analysis of criteria for brittle destruction of wood and its transition to a plastic state. The concept of virtual material transformation (CoViMT) forms the basis of the research. At the idea level, this concept is a variant of the well-known equivalent material concept (EMC). An integral criterion for brittle fracture was developed. Comparison with experimental data showed that the integral criterion and the known differential criterion lead to mismatched points of brittle fracture and transition of wood to the plastic state. Therefore, it is possible to determine the boundaries of the region of plastic states with the help of these criteria. Experiments confirmed the adequacy of the criteria when compressing wood with 6.4% and 18.0% moisture content. However, the volume of studies of the problem touched upon is small, so further research is necessary to better understand the stages of deformation of wood of different species.

Influence of V addition on the mechanical properties of FeCo alloys: a molecular dynamics study

Interatomic potentials for the Fe-Co and Fe-V binary systems have been developed based on an Fe interatomic potential with enhanced mechanical capabilities and merged to describe the Fe-Co-V ternary system based on the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. Emphasis has been placed on the correct prediction of FeCo elastic properties and antiphase boundary (APB) energies to ensure proper description of the mechanical behaviors. The potentials are then used to analyze the crack nucleation and propagation mechanisms in polycrystalline FeCo and FeCo-2V alloys under different ordering degrees at grain boundaries (GB) and within the grains. The results show that disordering inside grains has a larger impact on the ductility of the binary FeCo. The mobility of the antiphase domains (APD) inside the grains delays the ultimate tensile strength (UTS) and fracture point. The observed fracture procedure shows that triple junctions of GBs serve as the focal points of stresses concentration. The poor mobility at the triple GBs promotes crack nucleation and crack propagation, leading to an intergranular fracture in ordered and disordered binary alloys. The effects of adding 2 at. % V to the FeCo alloy have also been investigated via molecular dynamics (MD) and hybrid grand canonical Monte Carlo-MD (GCMC-MD) simulations. It was shown that V prefers to migrate to (a) the GBs in an ordered state, and (b) GBs and APBs in a disordered state. The ordered FeCo-2V displays a decreased UTS and loss of ductility at room temperature. Introducing V exclusively to the APBs greatly increases the mobility of APD and migration of atoms to GBs boosting the ductility of the alloy.

DETERMINATION, ANALYSIS AND SYNTHESIS OF THE ROOTS OF VALID ALGEBRAIC EQUATIONS USING LOGARITHMIC AMPLITUDE-PHASE FREQUENCY CHARACTERISTICS

The article considers the method of approximate determination, analysis and synthesis of the roots of real algebraic equations of high order. The solution of such problems is relevant in the case of designing information-measuring and control systems, studying the dynamics of movement of various mechanisms (industrial robots, quadrocopters, etc.), determining the trajectories of aircraft, etc. The analytical solution of such problems is limited to equations of the third (sometimes fourth) degree, in other cases it is necessary to use either special sequential algorithms or packages of applied computer programs such as "Wolfram.Matematica", which allow only to find the roots of the equations, but not to synthesize them. The proposed method is based on the application for the decomposition of the studied polyomial (corresponding to the equation) into the simplest multipliers corresponding to aperiodic and/or oscillatory links, asymptotic logarithmic amplitude and phase-frequency characteristics. The form and values of the roots of the equation are proposed to be judged by the slopes at the fracture points of the logarithmic amplitude and phase-frequency characteristics of the polyparticle under study. The construction of logarithmic amplitude and phase-frequency characteristics is carried out by discarding the "small" terms of the polygamy at separate frequency intervals. A feature of the method is the possibility of its use both in conjunction with the computer and without it. Manual use of the method assumes that the user has a calculator and a ruler. The method allows to determine not only the roots of real algebraic equations (both real and complex), but also to establish a visual relationship between the coefficients for the terms of the equations with the type and values of the roots and purposefully change the necessary coefficients to change the parameters and type of roots. The possibilities of the method are not limited to solving real algebraic equations with positive coefficients and integer powers, it shows quite satisfactory results for equations with mixed coefficients and fractional powers. The method is quite simple, clear, has a small error in the case of far spaced roots, but in the case of closely spaced roots, its error increases, although it remains quite acceptable. The article presents the substantiation of the method, shows numerous examples of its capabilities, compares the results obtained with the results obtained with the help of the package of applied computer programs "Wolfram.Matematica".

Grasping Local Participation: The Implementation of the Women, Peace and Security Agenda in the Western Balkans and North Africa

ABSTRACT This article focuses on those “points of fracture” (Kirby and Shepherd 2020, 12) that have manifested in the implementation of the Women, Peace and Security (WPS) Agenda in the Mediterranean region by examining National Action Plans (NAPs) in two distinct sub-regions – the Western Balkans and North Africa. We develop a comparative framework to shed light on the dimension of participation of these plans in four countries where the debate on WPS has reached different stages: Bosnia–Herzegovina, Kosovo, Tunisia and Morocco. By empirically investigating participation as both modality and focus of WPS debate and practice in these countries, we show that NAPs are unable to produce “meaningful local ownership” (Basini and Ryan 2016, 390) and that the international discourse on WPS should be re-thought to resonate with women’s needs, experiences and perspectives in post-conflict and post-revolutionary settings.

Spatial and Scalar Multitudes: Thinking with World, Globe, and Planet

Abstract: "Spatial and Scalar Multitudes: Thinking with World, Globe, and Planet" offers a theoretical framework and overview of the themed issue "World, Globe, Planet." This themed issue considers the recourse to macroscopic categories in early modern cultures and argues for their value as a resource for understanding present-day invocations of large-scale categories in conversations about the global, globalization, and geopolitics, on the one hand, and in conversations about the planetary, the environmental, and the Anthropocene, on the other. The tensions between such approaches encourage also a reconsideration of scale, interconnection, universality, modernity, cosmopolitanism, and other foundational concepts. Pieces in the collection, both scholarly and pedagogical, take up other keywords and points of fracture around totality, horizon, collectivity, and sphere.

Simulation and experimental investigation of the surgical needle deflection model during the rotational and steady insertion process.

Needle insertion is executed in numerous medical and brachytherapy events. Exact needle insertion into inhomogeneous soft biological tissue is of useful importance due to its significance in clinical diagnosis (especially percutaneous) and treatments. The surgical needles used in such processes can deflect during the percutaneous process. Needle deflecting which affects needle - soft tissue interface and needle controllability have a crucial role in establishment precision. In this paper, we have analyzed a mechanics-based model both rotational and non-rotational needle insertion, and studied the deflection phenomenon in both insertion cases, we validated it with a real-time nonlinear Dassault Systèmes® ABAQUS simulation model. For definite contact force, the maximum the contact stiffness was, the minimum it inserted, the cohesive surface model was used to investigate the needle insertion analysis, where the fracture point was defined by a failure strain and with the help of the in, the fully failed components would be removed. Using living tissue comparable PVA gel materials, the needle insertion force model is developed from insertion experimentations with the help of two different processes (rotational and non-rotational needle insertion). In a rotational needle, deflection is less than in a non-rotational needle. The preliminary insertion was observed in the rotational needle at 1.261 mm (experiment), and 1.538 mm (simulation), and for non-rotational needle insertion, the initial insertion was noticed at 1.756 mm (experiment) and 1.982 mm (simulation). The main aim of this study is to navigate the surgical needle in an accurate way to reduce the erroneousness for a clinical diagnosis like anesthesia, brachytherapy, biopsy, and modern microsurgery operation.

Fracture and Fatigue of Dental Implants Fixtures and Abutments with a Novel Internal Connection Design: An In Vitro Pilot Study Comparing Three Different Dental Implant Systems.

The aim of this study was to compare the mechanical behaviors of three dental implant fixtures with different abutment connection designs. Three implant systems were studied: the control (BLX implant), test group 1 (TORX++ implant), and test group 2 (IU implant). Three samples from each group were subjected to static compression to fracture tests to determine the maximum fracture load, and twelve samples were exposed to fatigue tests that measured how many cycles the implants could endure before deformation or fracture. Detailed images of the implant-abutment assemblies were obtained using micro-computed tomography imaging, and fractured or deformed areas were observed using a scanning electron microscope (SEM). The mean maximum breaking loads of 578.45 ± 42.46 N, 793.26 ± 57.43 N, and 862.30 ± 74.25 N were obtained for the BLX, TORX++, and IU implants, respectively. All samples in the three groups withstood 5 × 106 cycles at 50% of the nominal peak value, and different fracture points were observed. All abutment connection designs showed suitable mechanical properties for intraoral use. Microscopic differences in the fracture patterns may be due to the differences in the fixture design or abutment connection, and mechanical complications could be prevented by lowering the overload reaching the implant or preventing peri-implantitis.

Temperature effect on the mechanical behavior of shale: Implication for shale gas production

• The variation in mechanical strength parameters of shale at elevated temperatures. • Tensile strength, mode-I fracture toughness and point load strength investigation. • Mechanical strength attributes were supported with XRD and SEM analysis. • Micro-crack and thermal behaviour of minerals induced thermal behaviour of shale. Deformational shale attributes such as fracture toughness, tensile strength, and axial point load strength (PLS) index under elevated temperatures are crucial for the petroleum and gas industries. Here, an attempt has been made to investigate the thermal response of shale from room temperature to 400°C. Three-point bending (TPB) test using semi-circular bending (SCB) specimen, Brazilian tensile test, and the point load strength index test were conducted to evaluate mode-I fracture toughness, tensile strength, and PLS index, respectively, with varying temperatures. Additionally, the X-ray Diffraction (XRD) analysis was performed to determine the bulk rock composition and the resulting phase changes with increasing temperature. Furthermore, Scanning Electron Microscope (SEM) was used to study the induced microcracks in the sample due to thermal treatment. It was found that the mode-I fracture toughness increased from 25°C up to 100°C and, after that, a slight decline up to 400°C. The fracture toughness of the shale got increases from 0.256 MPa·m 1/2 to 0.454 MPa·m 1/2 in a transition from ambient room condition to 400°C. The same trend was obtained for tensile strength and PLS index. With the same temperature range, the tensile strength of the shale changed from 7.94 MPa to 9.75 MPa. The SEM images of the thermally treated samples demonstrate the formation of noticeable microcracks at 400°C.

Exploring the effect of relative humidity on dynamic evolution of flax fibre’s microfibril angle through in situ tensile tests under synchrotron X-ray diffraction

Tensile properties of elementary flax fibres were investigated through in situ Synchrotron X-ray diffraction in order to understand the effect of tensile loading, on the internal reorganisation of crystalline cellulose; for the first time, these experiments were conducted for different RH conditions. Synchrotron radiation experiments were considered under reduced spot size and short acquisition times to quantify the variation of cellulose microfibril angle (MFA) in a single fibre during tensile loading, while limiting the fibre damage during X-ray exposure. The acquisitions were possible at various relative humidity (RH) conditions (from 25 % to 92 %) in order to quantify the effects of different hygro-mechanical actions upon elementary flax fibres. The results show that the MFA decreases with the increase of the applied loading, indicating a partial realignment of the cellulose microfibrils with the loading axis. The MFA at fracture point shows a decrease between − 11 and − 15 % compared to the initial MFA at all relative humidity conditions studied. The strain at break of the fibres increases with increasing relative humidity. This mechanical behaviour shows the plasticizing effect of water on the non-cellulosic amorphous matrix of cell wall.

Physicochemical Characterization of Texture-Modified Pumpkin by Vacuum Enzyme Impregnation: Textural, Chemical, and Image Analysis

Texture-modified pumpkin was developed by using vacuum enzyme impregnation to soften texture to tolerable limits for the elderly population with swallowing and chewing difficulties. The impregnation process and macrostructural and microstructural enzyme action were explored by the laser light backscattering imaging technique and a microscopic study by digital image analysis. Texture was analyzed by a compression assay. The effect of enzyme treatment on antioxidant capacity and sugar content was evaluated and compared to the traditional cooking effect. Image analysis data demonstrated the effectiveness of the impregnation process and enzyme action on plant cell walls. Enzyme-treated samples at the end of the process had lower stiffness values with no fracture point, significantly greater antioxidant capacity and significantly lower total and reducing sugars contents than traditionally cooked pumpkins. The results herein obtained demonstrate the capability of using vacuum impregnation treatment with enzymes to soften pumpkins and their positive effects on antioxidant capacity and sugar content to develop safe and sensory-accepted texture-modified products for specific elderly populations.

Effects of plastic fragments on plant performance are mediated by soil properties and drought

In recent years, the effects of plastic contamination on soil and plants have received growing attention. Plastic can affect soil water content and thus may interact with the effects of drought on soil and plants. However, the effects of plastic on soil are highly context-dependent, and interactions with drought have been hardly tested. We conducted two greenhouse experiments to test the combined effects of plastic fragments (of varying size and concentration), water availability and soil texture, on soil water content and performance of the plant Arabidopsis thaliana. Plastic fragments had stronger negative effects on soil water content in low water availability, and the shape of this response (linear vs. unimodal) was mediated by soil texture. Conversely, increasing concentration of plastic had positive effects on plant growth. We suggest that plastic fragments introduce fracture points within soil aggregates. This increases number and size of soil pores favoring water loss but also facilitating root growth. Our results suggest complex interactive effects of plastic and drought, that may lead to a decoupling of plant and soil response. These processes should be taken into account in ecological studies and agricultural practices.

Helical single-walled carbon nanotubes under mechanical and electrostatic loading

Here, we characterize the axial response of helical single-walled carbon nanotubes (HSWCNTs) to mechanical and electrostatic loads, separately. The study considers low-pitch (closed) and high-pitch (open) HSWCNTs of different number of turns in their natural states. The computations are carried out using molecular dynamics near 0 K and at 300 K. Under mechanical loading, the low-pitch HSWCNTs show a bilinear load ( F ) - strain ( ϵ ) relation up to their elastic limit by overcoming; (i) the inter-coil van der Waals and the elastic restoring forces, and (ii) only the elastic restoring forces, in that order. However, a tunable plastic-like region emerges between the two linear regimes which is dependent of the number of active coils. Unloading of low-pitch HSWCNTs within the elastic limit exhibits hysteresis in F − ϵ graph. However, unloading both low- and high-pitch HSWCNTs from a point beyond their elastic limits results in accumulation of plastic strain. Electrostatic loading of HSWCNTs causes inter-coil Coulombic repulsion which after overcoming the van der Waal’s attraction between them and the mechanical restoring forces, produces a net elongation. Interestingly, the charge per atom ( q ) – strain ( ϵ ) graphs for the high-pitch HSWCNTs up to their elastic limit are found to follow the power law: q ∝ ϵ 3 / 5 . Discharging the HSWCNTs completely from a point beyond their elastic limit shows plastic deformation. Mechanical and electrostatic loading, unloading, and reloading of the HSWCNTs up to the fracture point are also examined. The study shows a direction towards developing nano-electro-mechanical actuators and precise positioners based on HSWCNTs.

Residual stress versus microstructural effects on the strength and toughness of phase‐separated PbO–B2O3–Al2O3 glasses

AbstractA few authors have reasonably proposed that liquid–liquid phase‐separated (LLPS) glasses could show improved fracture strength, Sf, and toughness, KIc, as the second phase could provide a barrier to crack propagation via deflection, bowing, trapping, or bridging. Due to the associated tensile or compressive residual stresses, the second phase could also act as a toughening or a weakening mechanism. In this work, we investigated five glasses of the PbO–B2O3–Al2O3 system spanning across the miscibility gap: Four of them undergo LLPS—three are binodal (two B2O3‐rich and one PbO‐rich) and one is spinodal—and one does not show LLPS (composition outside the miscibility gap). Their compositions were designed in such a way that the amorphous particles are under compressive residual stresses in some and under tensile residual stresses in others. The following mechanical properties were determined: the Vickers hardness, ball on three balls (B3B) strength, and toughness, KIc‐SEVNB (single‐edge V‐notch beam [SEVNB]). The microstructures and compositions were analyzed using scanning electron microscopy with energy‐dispersive X‐ray spectrometry. The spinodal glass showed, by far, the best mechanical properties. Its KIc‐SEVNB = 1.6 ± 0.1 MPa m1/2, which embodies an increase of almost 50% over the B2O3‐rich binodal composition, and 90% considering the PbO‐rich binodal composition. Moreover, its fracture strength, Sf = 166 ± 7 MPa, is one of the highest ones ever reported for an LLPS glass. Fracture analyses evidenced that the spinodal composition exhibited the lowest net stress at the fracture point. Moreover, calculations indicate that the internal residual stress level is the lowest in the spinodal glass. The overall results indicate that the microstructural effect of the spinodal glass is the most significant factor for its superior mechanical properties. This work corroborates the idea that LLPS provides a feasible and stimulating solution to improve the mechanical properties of glasses.

Theoretical and Experimental Study of the Effect of Plasma Characteristics on the Mechanical Properties of Ihram Cotton Fabric.

Theoretical and experimental investigations of the radial distribution function of the electron temperature (RDFT), for the abnormal glow region in a low-density plasma fluid and weakly ionized argon gas, are provided. The final proved equation of RDFT agrees with the experimental data for different low pressures ranging from 0.2 to 1.2 torr, confirming that the electron temperatures decrease with an increasing product of radial distance (R) and gas pressures (P). A comparison of the two configurations: for the axial distance (L), from the tip of the single probe to the cathode electrode, and the cathode electrode radius (R), shows that, in both cases, the generated plasma temperatures decrease, and densities increase. The RDFT accurately depicts a dramatic decrease for L < R by 60% compared with the values for L > R. This indicates that, when L < R, the rate of plasma loss by diffusion is reduced. Under this investigation, the mechanical characteristics of treated and pre-treated Ihram Cotton Fabric Samples were compared under the Influence of the different two configurations of Plasma Cell discharge: . These characteristics included resiliency, strain hardening, tensile strength, elongation percentage, yield strength, ultimate tensile strength, toughness, and fracture (breaking) point. Furthermore, the mechanism parameters of plasma interaction with textile membrane will be discussed, such as: process mechanism, interaction, and gas type.

Numerical and Experimental Mechanical Analysis of Additively Manufactured Ankle-Foot Orthoses.

Growing age and different conditions often require the replacement of orthoses, and FDM-based 3D printing can produce them quickly with less investment. In today’s market for orthotics, these characteristics are highly desired. Therefore, this study is fully focused on the optimization and strength analysis of FDM 3D-printed ankle–foot orthoses (AFO) fabricated using PLA and PLA reinforced with carbon fiber (PLA-C). An increase in ankle plantar-flexor force can be achieved by reinforcing thermoplastic AFOs with CFs. Specially designed mechanical strength tests were conducted at the UTM to generate force–displacement curves for stored elastic energy and fracture studies. The mechanical behavior of both AFOs was predicted with the help of an FEA. The model predictions were validated by comparing them with mechanical strength testing conducted under the same loading and boundary conditions as the FEA. In both the prediction and experimental analysis, the PLA-C-based AFOs were stiffer and could withstand greater loads than the PLA-based AFOs. An area of high stress in the simulation and a fracture point in experimentation were both found at the same location. Furthermore, these highly accurate models will allow the fabrication of AFOs to be improved without investing time and resources on trials.

Typescenes by Rodney A. Brown

Reviewed by: Typescenes by Rodney A. Brown Jeffrey Cyphers Wright (bio) typescenes Rodney A. Brown Unlikely Books https://www.unlikelystories.org/unlikely-books/typescenes 70 pages; Print, $13.00 Welcome to a vision where the mirror is simultaneously melting and regenerating … an experimental exercise hijacking poetic forms and reimagining them as philosophical inquiries into social heteromorphoses … an equationary leveler where volition and entropy are conflated. Recent literature has reflected civil upheaval and racial oppression with responses that record and research the soul of a nation. Claudia Rankine's Citizen: An American Lyric, from 2017, is a seminal text that employs hybrid methods and reached a large audience. The Ferguson Project, a series of interviews conducted by Ama Birch, focuses on a single tragedy through the eyes of community activists. Now we have a searing new entry in an unfolding genre of reality-based and structurally diverse methodologies for addressing and overcoming disparities. Rodney A. Brown's Typescenes centers on what Brown calls "component parts of Black living_which when read together create some singular convent of Blackness." And the twenty-five list poems (presented in prose) are singularly unique. Theoretical underpinnings are outlined in a foreword, a publisher's preface, and an author's preface, which together comprise about a third of the book. In a rigorous exegesis of the text, Jonathan J. Detrixhe declares, "This is no katabasis." No, for while recognizing unjust incidents and weaving them into a loose narrative, Brown does not leave us with a descent. We are instead, [End Page 156] offered more, not less. The world opens rather than shrinks. The reader is given agency rather than being diminished. Detrixhe continues: "From the poet we get self-overcoming on a massive scale, but we also get the torture chamber in which the training for mastery took place." This book is built on one word: enter. This word is repeated about a thousand times, serving as a mechanism to introduce elements to the "typescenes." Yet exit, the natural obverse of enter, is scarce, implying that once entered, a mark remains. This a book you have to make space for, to let it enter you. And remember, enter has more than one meaning. An entry can be made into a place or an entry can be made into a diary or ledger. Brown plays with that duality between physical and verbal. A dancer (and founder of the Brown Dance Project) as well as a writer, the author originally created these "typescenes" as part of a performance, merging the meanings of enter. Multidisciplined, the work gives new ballast to the term "body of work." "Many beautiful minds continue to write about music," the publisher notes, "but fewer have the nerve to create a nonmusical work designed for dancing. Typescenes is such a work: some thirty-nine pages of dense language." Like good music without choreography, the book holds up without the accompaniment of dance. The subject matter and iterative rhythms call for contemplation about our evolution. It's worth quoting a longer sample from the first poem, "The Nightmare Passenger," to frame what will be an immersive, perhaps even cathartic, experience for a reader. In this opening salvo, Brown boldly outlines strategies, asking the reader what they might expect from this text and what's expected of them in return: Enter you own God. Enter words. Dance go. Enter worthlessness feelings. Enter the sound of your own voice. Mix that, the first, voice into a socratic seminar with the other voices present. Enter toy. Enter cultural trade. Enter aftermath. Enter activism. Enter results. Enter directions. The text confronts iniquity and suggests a capacity for responsibility. "Enter people in great financial need and those with lesser need." It reassembles iconic symbols of oppression: "Enter untaxed cigarettes." "Enter chokeholds." [End Page 157] The work stacks, fabricating a rich texture of wounds and resolutions, amulets and insults. "Black experience enter. Enter verdicts." "Enter selling cotton." Reminders of grievances mingle with chances for dignity. "Enter second chances. Enter third chances. Enter fourth chances." Brown finds the fracture points in the politics of our day … in the wake of the BLM movement … in the ongoing subjugation of minorities. The work offers a view...

Impact of high-pressure balloon aortic valvuloplasty on the hydrodynamic result after a transcatheter valve-in-valve procedure.

The aim of this study was to investigate the degree of functional improvement of a transcatheter heart valve (THV) for valve-in-valve after bioprosthetic valve fracture (BVF) of three small surgical aortic valve bioprostheses (SAVBP) using high-pressure balloon aortic valvuloplasty (HP-BAV) under standardized ex-vivo-conditions. A THV 26 mm (Evolut R) and SAVBP 21 mm (Perimount Magna Ease, Trifecta, and Epic supra [n = 4] were used. Mean pressure gradient (MPG), effective orifice area (EOA), geometric orifice area (GOA), minimal internal diameter (MID), and pinwheeling index (PWI) were analyzed before and after HP-BAV of the SAVBP using a noncompliant balloon. Fracturing of the SAVBP was done before implantation of the THV and the balloon pressures at the point of fracture were recorded. The Magna Ease and Epic fractured at balloon pressures of 18 and 8 atm, respectively. The Trifecta did not fracture up to a balloon pressure of 30 atm but was dilated. HP-BAV led to increased THV expansion as evident by straightened coaptation lines of the Evolut R 26 mm with reduced PWI, increased MID, and increased GOA in all 21 mm SAVBP. Evolut R showed significantly lower MPG and higher EOA as ViV in all prostheses after HP-BAV (p &lt; 0.001). MPG and EOA of Evolut R differed regarding the SAVBP. Evolut R presented the lowest MPG and highest EOA in Magna Ease and the highest MPG and lowest EOA in Epic supra. The degree of function improvement of the same THV as ViV after HP-BAV depends on the surgical valve model. Functional improvement can also be achieved without valve fracture.

Applying the new experimental midpoint concept on strain energy density for fracture assessment of composite materials

A mixed-mode I/II fracture criterion for predicting the fracture response of composite materials is proposed. This criterion is derived based on a comprehensive study and the consideration of the physics of fracture onset. The fracture phenomenon that causes the various damage mechanisms at the vicinity of the crack tip is examined. It is elucidated that the stress distribution at the crack tip ought to be defined using the reinforcement isotropic solid (RIS) stress state. This new criterion, which is called Improved Strain Energy Density with Mid-point (ISEDM), includes the effect of the fracture process zone (FPZ) and T-stress, which remarkably affect the mixed-mode fracture process, particularly, when mode II is dominant. Substituting the strain energy density in a pure mode I with the strain energy density in the midpoint of mixed-mode I/II is the creative idea employed in proposing this criterion. Because in pure mode I the effects of FPZ are minimal, change of fitting point on fracture limit curve (FLC) from KIc to midpoint critical stress intensity factors (CSIF’s) makes it possible to consider the effects of FPZ more accurately. In the ISEDM criterion, fracture behavior depends on mechanical properties and CSIF’s of the midpoint. Crack initiation angle is considered along minimum strain energy density and this angle is derived in the midpoint of mixed-mode I/II. RIS theory is used as an applicable theory for modeling orthotropic materials in this paper and causes valid and reliable fracture behavior to be extracted. In addition, changing fracture point from pure mode I to the mid-point of experimental data causes the effects of FPZ to be considered without estimating the toughening mechanisms in this zone, and the fracture behavior is extracted with higher accuracy. FLC’s in comparison with available experimental data prove that the ISEDM criterion anticipates the fracture behavior of orthotropic materials well. Finding KIIc based on the analytical method is a valuable achievement. In this article, KIIc can be predicted with appropriate accuracy, only by CSIF’s of mid-point and using ISEDM criterion.