Cleavage Stresses Research Articles

Transcriptomic and Physiological Analyses Reveal Potential Genes Involved in Photoperiod-Regulated β-Carotene Accumulation Mechanisms in the Endocarp of Cucumber (Cucumis sativus L.) Fruit.

The accumulation of carotenoids in plants is a key nutritional quality in many horticultural crops. Although the structural genes encoding the biosynthetic enzymes are well-characterized, little is known regarding photoperiod-mediated carotenoid accumulation in the fruits of some horticultural crops. Herein, we performed physiological and transcriptomic analyses using two cucumber genotypes, SWCC8 (XIS-orange-fleshed and photoperiod-sensitive) and CC3 (white-fleshed and photoperiod-non-sensitive), established under two photoperiod conditions (8L/16D vs. 12L/12D) at four fruit developmental stages. Day-neutral treatments significantly increased fruit β-carotene content by 42.1% compared to short day (SD) treatments in SWCC8 at 40 DAP with no significant changes in CC3. Day-neutral condition elevated sugar levels of fruits compared to short-day treatments. According to GO and KEGG analyses, the predominantly expressed genes were related to photosynthesis, carotenoid biosynthesis, plant hormone signaling, circadian rhythms, and carbohydrates. Consistent with β-carotene accumulation in SWCC8, the day-neutral condition elevated the expression of key carotenoid biosynthesis genes such as PSY1, PDS, ZDS1, LYCB, and CHYB1 during later stages between 30 to 40 days of fruit development. Compared to SWCC8, CC3 showed an expression of DEGs related to carotenoid cleavage and oxidative stresses, signifying reduced β-carotene levels in CC3 cucumber. Further, a WGCNA analysis revealed co-expression between carbohydrate-related genes (pentose-phosphatase synthase, β-glucosidase, and trehalose-6-phosphatase), photoperiod-signaling genes (LHY, APRR7/5, FKF1, PIF3, COP1, GIGANTEA, and CK2) and carotenoid-biosynthetic genes, thus suggesting that a cross-talk mechanism between carbohydrates and light-related genes induces β-carotene accumulation. The results highlighted herein provide a framework for future gene functional analyses and molecular breeding towards enhanced carotenoid accumulation in edible plant organs.

Correlating point defects with mechanical properties in nanocrystalline TiN thin films

Defects significantly affect the mechanical properties of materials. However, quantitatively correlating the point defects with mechanical property could be a challenge. In this study, we explore the point defect effects on the structure and property of magnetron sputtered TiN nanocrystalline films (synthesized using different negative bias potential) via a combination of analytical techniques and density functional theory (DFT) calculations. We gain insights into the structural evolution and properties of nanocrystalline films at different length scales. It is found that nanocrystal microstructure and local electronic structure triggered by various point defects remarkably change. Along with the structural evolution and point defect changes, the electrical conductivity and the fracture toughness of TiN are improved. Furthermore, the fracture toughness, Young’s modulus, and cleavage energy and stresses for TiN films with different point defect structures are calculated. The experimental data is in excellent agreement with first-principle calculations. Our results suggest a direct correlation of the point defect structure with TiN films' mechanical properties.

Refined Mathematical Model of the Stress State of Adhesive Lap Joint: Experimental Determination of the Adhesive Layer Strength Criterion

A new mathematical model of adhesive joint was developed and experimentally validated, in which the Vlasov–Pasternak two-parameter elastic bed model was used to simulate the stress state of the bonding layer. According to this elastic model, the adhesive layer was regarded as a membrane located in the middle of the adhesive layer thickness, between which and the bearing layers there were elastic elements. The outer bearing layers were regarded as beams in the Timoshenko approximation. The tangential stresses were considered to be constant across the thickness of the adhesive layer, and the normal (cleavage) stresses to be variable. This approach allows one to describe different types of boundary conditions for tangential stresses in the adhesive layer at the ends of the adhesive line, viz.: there are no tangential stresses at the edge of the adhesive joint if there are no adhesive spews, or the tangential stresses reach a maximum at the edge of the adhesive line if these spews exist. The problem was reduced to a system of ordinary differential equations in displacements and rotation angles of bearing layers. The system was solved by the matrix method. It was found that the sagging of the adhesive greatly reduced the maximum cleavage stresses in the adhesive layer. Tensile tests of adhesive lap-jointed metal rods were carried out. The proposed model was used to evaluate the strength criterion of the adhesive layer. It was shown that the best approximation of calculated and experimental data was provided by the maximum principal stress criterion. The proposed approach can be used to solve joint design problems.

Mechanical behavior of (Ni, Fe)Cr2O4 spinel grain boundaries studied by molecular dynamics simulations.

Using molecular dynamics simulations, we study the fracture initiation of grain boundaries in NiCr2O4 and FeCr2O4 of spinel structure. These compounds are representative of corrosion layers of nickel-chromium-iron austenitic stainless alloys. Uniaxial deformation is applied to several symmetric tilt-, twist-, and random-grain boundaries until complete decohesion is reached, in order to measure the critical cleavage stresses. We find that this mechanical quantity depends on the chemical composition and the structure of the grain boundaries. A correlation between the critical stress and the misorientation angle of the grain boundaries can be established. It is also found than the twist- and the random-grain boundaries exhibit the weakest resistance. Furthermore, these simulations show a localization of the elastic response in the vicinity of the grain boundary plane. Therefore, we were able to compare our simulation results with those provided by the theoretical model based on the universal binding energy relation that relates the critical stress to the cleavage grain boundary energy. It shows that this model provides similar critical stresses than the molecular dynamics simulations if the localization distance parameter is defined as the distance related to the deformation of the grain boundary thickness during the deformation.

ADAIS: Automatic Derivation of Anisotropic Ideal Strength via high-throughput first-principles computations

Anisotropic ideal strength is a fundamental and important plasticity parameter in scaling the intrinsic strength of strong crystalline materials, and is a potential descriptor in searching and designing novel hard/superhard materials. However, to the best of our knowledge, an automatic derivation of anisotropic ideal strength has not been implemented in any open-source code available so far. In this paper, we present our developed ADAIS code, an automatic derivation of anisotropic ideal strength via high-throughput first-principles computations for both three-dimensional and two-dimensional crystalline materials with any symmetry, as well as for an ideal interface model. Several fundamental mechanical quantities can be automatically derived, including ideal tensile and shear strengths through affine deformation, universal binding energy and generalized stacking fault energy, as well as the ideal cleavage and slide stresses through alias deformation. The implementation of this code has been comprehensively demonstrated and critically validated by a lot of evaluations and tests of various crystalline materials with different symmetry, indicating that our code could provide a high-efficiency solution to quantify the strength of strong solids. Program summaryProgram title: ADAISProgram Files doi:http://dx.doi.org/10.17632/336hry5g66.1Licensing provisions: BSD 3-ClauseProgramming language: Fortran90Nature of problem: A scheme adapted to high-throughput first-principles computations is much necessary to automatically determine the anisotropic ideal strength along any crystallographic orientation under affine and alias deformations for crystalline solids with any symmetry.Solution method: To derive the ideal strength of a crystalline solid along a specific crystallographic orientation, a projection and/or redefinition of a lattice are firstly performed. The affine (alias) deformation is then applied to the projected (redefined) lattice, and a relaxation is done on the distorted structure by the simply modified VASP code optimizer with certain cell constraints. Afterwards, the resultant total energies and stresses vs strain are generated accordingly. Finally, the anisotropic ideal strengths are derived from the calculated stress/energy–strain relationship, and meanwhile the variation of bond length as a function of strain is revealed to illustrate the failure mode. Whenever an unexpected error happens, a message will be printed for further evaluation.

Cleavage fracture assessment of cold charged steel slabs using experimental and numerical approaches

Drop Weight Tear Test (DWTT) set-up has been used to investigate cleavage fracture of steel slabs at different elevated temperatures up to 500°C. Fracture surfaces of broken samples have been analyzed using Scanning Electron Microscope (SEM) to understand ductile and brittle fracture appearances at the elevated temperatures. The eXtended Finite Element Method (XFEM)-based cohesive segment technique has been used to simulate the dynamic crack propagation of the DWTT at all tested temperatures. The obtained numerical results were in good agreement with the observed experiments. Eventually, a hybrid experimental-numerical method is proposed to define a set of critical cleavage stresses for cold/hot charged steel slabs.

Geometric Factors Impacting Adhesive Lap Joint Strength and Design

Too often adhesive thickness, adherend thickness and other geometric factors are not explicitly considered in adhesive joint design. This study includes experimental and computational research exploring the means of enhancing the engineering design process for adhesive lap joints to include such effects. It clearly demon-strated that both the cleavage stresses and the shear stresses, near the bond termini, play important roles in lap 'shear' joint failure. Finite Element and Fracture Mechanics analyses were used to examine the energy release rate applied to growth of cracks in adhesive lap joints. Lap joints with similar geometries to those analyzed were designed, fabricated and tested. In a separate set of experiments the bond termini were constrained in the direction normal to the uniaxial loading. If the strength of lap shear joints is dominated by the adhesive shear strength, then constraining the lateral motion of the bond termini should have little or no effect on the overall shear strength of the adhesive joint. This work clearly demonstrates that this is not the case. If cleavage stresses are important in lap joints then constraining the bond termini, in a direction normal to the bond area, should have a commensurate effect on the overall strength of the lap joint. None of the ASTM standardized 'lap shear tests' provide any insight into this premise. This paper also presents analyses and experimental results for lap joints to which several methods of lateral constraint were applied near the bond termini. The analytical and numerical methods described and used for explaining and predicting such effects might be a useful adhesive joint design tool.

Method for the calculation of the stress fields for a wedge-shaped twin located at the surface of a crystal in the approximation of a continuous distribution of twinning dislocations along twin boundaries

A method is proposed to calculate the stress fields for a wedge-shaped twin located at the crystal surface. A graphic representation of the configuration of the fields of normal and cleavage stresses of a wedge-shaped twin has been obtained. It has been found that the stresses are localized not only at the twin boundaries and at its apex, but also in certain regions distant from the boundaries.

Calculation of the stress fields in a polysynthetic twin located near the crystal surface

Without using the thin twin approximation, assuming a continuous distribution of dislocations on the boundaries, a procedure to calculate the stress fields in a polysynthetic twin located near the crystal surface has been developed. It is shown that the stresses in the polysynthetic twin are localized at the boundaries and apices of the twins that enter into the composition of the former twin. Examples of calculations of the cleavage stresses of the polysynthetic twin having rectilinear and curvilinear boundaries with uniform and nonuniform distribution of dislocations at them are given.

Cleavage fracture of a crystal: Density functional theory calculations based on a model which includes structural relaxations

Based on density functional theory calculations, we study cleavage under loading mode I, in which the atomic layers are allowed to relax after a crack with a given opening was initiated. By introducing the new materials parameter ${l}_{r}$, the critical opening for relaxed cleavage, we derive a simple analytic formulation describing the decohesion energy and the corresponding stress for relaxed cleavage. In this model, for crack openings smaller than $x<{l}_{r}$ we assume linear elastic behavior, i.e., a quadratic form of the decohesive energy ${E}_{r}(x)=\frac{{G}_{r}}{{l}_{r}^{2}}{x}^{2}$, in which ${G}_{r}$ is the cleavage energy for structurally relaxed cleavage surfaces. The general applicability of this model is demonstrated by applying it to materials with different bonding properties, such as metals, intermetallic compounds, SiC, and Si. It turns out that the values of ${l}_{r}$ are equal or very similar to the localization length ${L}_{b}$ for ideal brittle cleavage as introduced recently [Lazar et al., Appl. Phys. Lett. 87, 261910 (2005)], manifesting that at the atomic scale the elastic energy during cleavage is a localized quantity. Critical or maximum stresses for relaxed cleavage ${\ensuremath{\sigma}}_{r}=2\frac{{G}_{r}}{{l}_{r}}$ are significantly larger than the stresses for ideal brittle cleavage, which is discussed in detail. Relations between cleavage stresses and cleavage energies or the uniaxial rigid elastic moduli are analyzed.

Dependence of critical cleavage stresses as a function of orientation and temperature in single crystals of Fe-18% Cr-14% Ni-2% Mo austenitic stainless steel containing hydrogen

The effect of electrolytic hydrogen saturation on the critical cleavage stress τ cr was studied as a function of test temperature, duration of hydrogen saturation, and orientation of the tension axis in single crystals of Fe-18% Cr-14% Ni-2% Mo austenitic stainless steel.

Thermal cleavage stresses in a piecewise-homogeneous plate

We analyze the thermal stressed state of a piecewise homogeneous body formed by a homogeneous matrix and a layer with different thermal properties applied to its surface. The free surface of the layer is heated by a uniformly distributed heat flow of limited duration. On the basis of the solution of the corresponding nonstationary boundary-value problem of heat conduction, we determine the fields of quasistationary thermal stresses and strains. The numerical analysis is performed to show the possibility of using the obtained solutions in modeling thermal cleavage of brittle materials.

Atomic-scale ab initio study of the Zr–H system: II. Interaction of H with plane defects and mechanical properties

The interaction of hydrogen with plane defects (free surfaces and stacking faults SF) in the α-Zr–H solid solution was studied using ab initio calculations based on density functional theory. A high amount of H strongly lowers surface excess energies but has little influence on critical cleavage stresses, in contradiction with usual models correlating both quantities. H significantly reduces SF excess energies, thus possibly enhancing planar slip and hindering cross-slip, in agreement with the predictions of the hydrogen-enhanced localised plasticity (HELP) model.

Novel Design of a Bonded Lap Joint

A new design of a single-lap joint was proposed and investigated experimentally. In this new design, load eccentricity as well as singular peel stresses in the joint interface were avoided. In fact, numerical calculations show that, in the new design, the peel stress becomes compressive in the joint end region, and the shear load is more evenly transferred over the length of the joint. Two adherend layups, that is, (0/90/0/90) 2s and (90/0/90/0) 2s, were considered. Experimental results show that the strength of the new joint is signie cantly higher than that of the conventional single-lap joint. It is believed that even higher strength can be obtained by optimizing the new design cone guration. ANY structures consist of a number of basic parts that are connected together to take up the load. The connections or joints are usually the weakest locations in the structure. Among the many technical challenges facing engineers using advanced com- posite materials is joining composite parts or composite to metallic components.Eventhoughtheuseofcompositematerialscangreatly reduce the number of parts, joining parts is still unavoidable. Tradi- tional joining methods for metals such as welding and soldering are apparently unsuitable for e ber-reinforced composites. Compared to mechanical fastening, adhesive bonding is attractive for joining e ber-reinforced composite structures because it reduces the local- ized stresses encountered when using bolts and rivets. Moreover, bolts and rivets cut the continuous reinforcing e bers, and, as a re- sult, may greatly reduce the overall load carrying capacity of the structure. Adhesively bonded joints are used in many different cone gura- tions, among which the most commonly used are single-lap joints, double-lap joints, scarf joints, and step-lap joints. 1 3 The single-lap jointisgenerallythesimplestandleastexpensiveofalljointstoman- ufacture. However, because of its intrinsic load eccentricity and the abruptchangeofload path,boththe normal (peel)and shearstresses are highly localized at the two joint ends; thus, the conventional lap jointsare not efe cient in load transfer. 4 Moreover,because theinter- facial normal stress is tensile and theoretically singular at the joint ends, it can initiate failure at these locations. Although tapering the adherend or adding adhesive e llets at joint ends can lead to some reduction of peel stresses in the lap joint, these improvements are, however, quite modest. 5;6 Structural adhesives have relatively poor resistance to peel or cleavage stresses. Therefore, an obvious step to improve joint strength is to reduce the magnitude of peel stress or to make it compressive. To obtain maximum joint efe ciency, the interfacial shear stress distributions should also be made more uniform. In this paper, a newwavy bonded lap joint is proposed and inves- tigated. With this new joint design, the interfacial normal stress is compressiveatthetwojointends,andtheinterfacialshearstressdis- tribution is less localized. Experimental results show that the wavy joint has much greater strength than the conventional lap joint. Conventional Single-Lap and New Wavy-Lap Designs For comparison, a two-dimensional sketch of the conventional single-lap joint is shown in Fig. 1. Only the case of identical ad- herends is considered in this study. The length of both outer ad- herends is L, the overlap (joint) length is l, and the thickness of adherend and adhesive are ta and tg, respectively. the waviness angles (Fig. 2) ® DD tan 1 .2ta=l 0 ) and round out sharp corners of the joint with an adequate radius R. The e nal joint shape selected is shown in Fig. 3. The shape chosen here is mainly for simplicity; other possible shapes may be as effective. Strictly speaking, the two adherends in this wavy joint are not in a collinear cone guration. The dashed lines in Fig. 2 show this. If a collinear cone guration is desired, then the thickness of the adhesive must be taken into account during the e rst design step. Because the thickness of the adhesive is very small compared with that of the adherends in this study, it is neglected during the design process. The values of the geometrical parameters for both conventional and wavy joints are given in Table 1. Even though l 0 <l, the overall bonding areas are the same for the two joints. This ensures that analysis and test results of these joints can be directly compared. TheonlydimensionthatisnotshownintheFigs.1and2isthewidth of specimen, which is d D25:4 mm. The material for adherends is AS4/3501-6 carbon/epoxy. Two different layups, (90/0/90/0) 2s and (0/90/0/90) 2s, are used. The 0-deg direction is parallel to the longitudinal (loading)directionofthejoint.Thereasonforchoosing these two layups is to study the difference between 90 -90 deg and 0-0 deg bonding interfaces. The material constants of AS4/3501-6 are listed in Table 2. The two adherends are bonded together with a layer of e lm adhesive FM73M, which is treated as an isotropic material.Theelastic constants forFM73Mare also listed in Table2.

K562 cells implicate increased chromatin accessibility in Alu transcriptional activation.

Alu repeats in K562 cells are unusually hypomethylated and far more actively transcribed than those in other human cell lines and somatic tissues. Also, the level of Alu RNA in K562 cells is relatively insensitive to cell stresses, namely heat shock, adenovirus infection and treatment with cycloheximide, which increase the abundance of Alu RNA in HeLa and 293 cells. Recent advances in understanding the interactions between DNA methylation, transcriptional activation and chromatin conformation reveal reasons for the constitutively high level of Alu expression in K562 cells. Methylation represses transcription of transiently transfected Alu templates in all cell lines tested but cell stresses do not relieve this repression suggesting that they activate Alu transcription through another pathway. A relatively large fraction of the Alus within K562 chromatin is accessible to restriction enzyme cleavage and cell stresses increase the chromatin accessibility of Alus in HeLa and 293 cells. Cell stress evidently activates Alu transcription by rapidly remodeling chromatin to recruit additional templates.

Theory and Analysis of Peel Adhesion: Adhesive Thickness Effects

Abstract The existing assumptions concerning boundary stress concentrations in peel adhesion are extended to treat the effects of adhesive thickness. In adhesive bonds involving the all-angle peeling of a flexible elastic adherend from a rigid substrate the varying of adhesive thickness is shown theoretically to predict a proportional increase of peel force (P) with adhesive interlayer thickness (a) when the product (βCa) of the cleavage stress concentration β, cavitation scale factor C, and adhesive thickness a is less than unity. When the product (βCa) becomes greater than unity the new theory predicts that cleavage stresses concentrate within a fractional layer of the total adhesive thickness f(a) and the peel force P tends to achieve a constant value Pmax. This new theory is verified by experimental studies and the experimental analysis suggests new optimizations in the design and measurement of the peel adhesive bond.

A tensile stress criterion for cleavage in precracked, notched and smooth bars

Using a statistical model derived for cleavage induced by hard particles, an analysis has been carried out of a newly defined critical tensile stress for cleavage, i.e. the statistical mean stress with respect to cleavage fracture probability. The results of the analysis show that the critical tensile stress (cleavage stress) is highest for a precracked bar, intermediate for a notched bar and lowest for a smooth bar, owing to the fact that small particles are possible to trigger cleavage when stress distribution in a bar is uneven. The cleavage stress for the precracked bar is found to decrease rapidly with increasing temperature while those for the notched and smooth bars remain almost constant. The cleavage stresses for the precracked, notched and smooth bars can be correlated through a definite formula. For a pure-bending notched bar, the conventional cleavage stress (maximum stress in the bar) is found to be a good approximation of the new cleavage stress. The difference between the two will increase when stress gradient becomes steeper.

Crack in an imperfect interface in composites

The behavior of cracks at the interface of composites is studied. The geometry of the composite is idealized as two-dimensional, isotropic, linearly “elastic” infinite strips made of two different materials joined by a damaged layer approximated by continuous distributed shear and tension springs. The damage considered in the layer is an interface crack. A general formulation is developed in terms of two simultaneous integral equations. An asymptotic analysis of the integral equations based on Muskhelishvili's techniques reveals logarithmic singularities in the normal (cleavage) stresses and strain functions at the crack tips. The special case of two bonded half-planes is also discussed. Parametric studies at a microscopic level are conducted for an interphase crack between the fiber and the matrix, and at a macroscopic level for an adhesive layer crack between two laminae.

The application of coherent optics to the study of adhesive joints II. Holographic interferometry

AbstractThe technique of holographic interferometry is complementary to the technique of speckle photography described previously. It allows the out‐of‐plane motion to be visualized with a sensitivity of about 0.3 μm. This technique has been applied to the study of the behavior of model glass‐glass joints bonded by different adhesives under shear stress. Its high sensitivity allowed the presence of stress concentrations at the ends of the joints to be shown in the case of high‐modulus adhesives and the existence of additional torsion and/or cleavage stresses to be demonstrated in the case of lower modulus adhesives. Work in progress should lead to more quantitative data.

Dislocation retardation due to the destruction of short-range order in the L12 superstructure

The magnitude and temperature dependence of the dislocation retardation due to the destruction of short-range order are calculated in the quasichemical approximation. The atomic interaction in two coordination spheres and dislocation slip in cubic and octahedral planes are taken into account. The retardation stress for the first superdislocation is essentially the same in these planes for T < T k (where T k is the phase-transition temperature), while the retardation stress for subsequent superdislocations is much lower, so large planar accumulations of superdislocations may arise. The retardation stress is maximal at T = T k , and for T > T k the first dislocations should move in pairs. Comparison of the experimental cleavage stresses with calculated values shows that, by itself, superdislocation retardation due to correlation destruction cannot explain the behavior of the yield point.