Surface Tensile Strain Research Articles

Investigation on cracking characteristics of Al–Si coating on hot stamping boron steel parts based on surface strain analysis

The purpose of this study is to investigate the relations between surface strains and cracking characteristics of Al–Si coating on hot stamping parts. A high-temperature laser confocal microscope system was used to dynamically observe coating surface appearance evolution during tensile procedure. The results suggest that the cracking behavior of Al–Si coating after austenization shows a strong sensitivity to tensile deformation. Based on hot tensile tests of coated boron steel on Gleeble 3500, Johnson-Cook constitutive parameters were solved and adopted in forming simulations to calculate surface strain distributions of two U-shape parts with different geometries. Hot stamping experiments of the parts were also conducted for coating detection. Coating cracking characteristics including crack morphology, crack width distribution and crack density were obtained using scanning electron microscope and optical microscope. The results indicate that widened coating macro-cracks are dominant in regions subjected to tensile surface strains. At a tensile surface strain higher than 2%, through-thickness macro-cracks are widely distributed in the coating. Additionally, macro-crack width variation in coating shows a similar trend with surface strain distribution. A higher strain rate could weaken this similarity and result in larger crack density and smaller crack width difference. To sum up, it could be feasible to estimate coating cracking characteristics of hot stamping parts based on surface strain analysis.

Spatially arranged chains of Ge quantum dots grown on Si substrate prepatterned by ion‐beam‐assisted nanoimprint lithography

AbstractJoint experimental and theoretical study of Ge nanoislands growth on groove‐patterned Si(001) substrate prepared by ion‐beam‐assisted nanoimprint lithography is carried out. Prepatterning procedure includes ion irradiation of Si substrate through imprinted resist mask with linear mounds and subsequent multistep oxidation/etching of irradiated Si domains. It is shown that the temperature of subsequent heteroepitaxy on the groovepatterned substrate affects the location of Ge nanoislands. The effect is attributed to additional surface tensile strain formed inside grooves by residual irradiationinduced defects. The interplay of strain and surface curvature makes the critical size of 3D nanoisland larger at the concave regions in grooves than between them. At lower temperatures this results in nanoisland nucleation at the top of mounds. At higher temperatures due to the intensive migration of Ge inside grooves the formation of large nanoislands in grooves occurs. The effect of temperature on the location and size of nanoislands is described by Monte Carlo simulations. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Lateral Displacement of the Grip on Single lap Composite-to-Aluminum Bolted Joints

Single lap bolted joints subjected to tensile load are essential joining methods in engineering design. Lateral displacement of the grip in single lap bolted joint experiment was examined and analyzed. This was different from early investigations that considered the joint fully gripped with no lateral degree of freedom. The lateral stiffness of the grip was tested to obtain the test machine properties. Tensile experiments on single lap composite-to-aluminum bolted joints were conducted, and the lateral displacement of the grip measured. Other measurements included tensile displacement, out-of-plane displacement, and surface strains. By allowing for lateral displacement, the novel finite element model predicted good results. The influence of lateral displacement of the grip was analyzed using the novel and traditional models. The novel model predicted 13 % smaller joint stiffness than traditional model. The parameters related to secondary bending were found different and the failure load of the joint was delayed because of lateral displacement of the grip.

Influence of the tensile strain on CH4 dissociation on Cu(1 0 0) surface: A theoretical study

Tensile strain is widespread on the catalyst surface due to the lattice mismatch between the catalyst and substrate, such as Cu/MgO in this work. Thus, it is important to investigate the influence of tensile strain on the catalytic properties. In this study, we have investigated the CH4 dissociation on Cu(100) surface by considering the tensile strain. Our results showed that compared with the unstrained Cu(100) surface, the most stable sites for dissociation species CHx (x=0⿿3) and H adsorption on strained surface remain unchanged. The surface strain strengthens CHx (x=0⿿3) adsorption, while weakens H adsorption. The elementary reaction for CH4 dissociation with the largest electronic energy barrier changes from CH⿿C+H on the unstrained surface to CH4⿿CH3+H on the strained surface (for strain equal to and larger than 3%), in agreement with the experimental observation that CH4 dissociation into CH3 and H is the most difficult reaction. The tensile strain accelerates C migration while has no obvious influence for C polymerization. Both DFT calculations and microkinetic model demonstrated that the strain hinders the CH4 dissociation process on Cu(100) surface. CH4 dissociation rate depends sensitively on the magnitude of the surface tensile strain.

Cartilage Strain Distributions Are Different Under the Same Load in the Central and Peripheral Tibial Plateau Regions

There is increasing evidence that the regional spatial variations in the biological and mechanical properties of articular cartilage are an important consideration in the pathogenesis of knee osteoarthritis (OA) following kinematic changes at the knee due to joint destabilizing events (such as an anterior cruciate ligament (ACL) injury). Thus, given the sensitivity of chondrocytes to the mechanical environment, understanding the internal mechanical strains in knee articular cartilage under macroscopic loads is an important element in understanding knee OA. The purpose of this study was to test the hypothesis that cartilage from the central and peripheral regions of the tibial plateau has different internal strain distributions under the same applied load. The internal matrix strain distribution for each specimen was measured on osteochondral blocks from the tibial plateau of mature ovine stifle joints. Each specimen was loaded cyclically for 20 min, after which the specimen was cryofixed in its deformed position and freeze fractured. The internal matrix was viewed in a scanning electron microscope (SEM) and internal strains were measured by quantifying the deformation of the collagen fiber network. The peak surface tensile strain, maximum principal strain, and maximum shear strain were compared between the regions. The results demonstrated significantly different internal mechanical strain distributions between the central and peripheral regions of tibial plateau articular cartilage under both the same applied load and same applied nominal strain. These differences in the above strain measures were due to differences in the deformation patterns of the collagen network between the central and peripheral regions. Taken together with previous studies demonstrating differences in the biochemical response of chondrocytes from the central and peripheral regions of the tibial plateau to mechanical load, the differences in collagen network deformation observed in this study help to provide a fundamental basis for understanding the association between altered knee joint kinematics and premature knee OA.

An experimental investigation on the damage of granite under uniaxial tension by using a digital image correlation method

This paper presents an experimental investigation of the damage mechanisms of granites under uniaxial tension. The displacement distribution and surface tensile strain of the specimens were measured by using a digital image correlation (DIC) method. A substantially large strain localization region emerged on the surface of the specimens before the tensile stress approached its ultimate value; subsequently, this strain localization region coincided with the final crack. Based on the measured tensile strain, a parameter was proposed to describe the average gradient of the tensile strain. This parameter was found to be much larger near the crack than in the other regions. Experimental results showed that the damage was related to the strain as well as to the strain gradient. These results may provide a practical foundation for a new gradient damage theory for rocks under tensile loading.

Nucleation and epitaxial growth of Ge nanoislands on Si surface prepatterned by ion irradiation

Experimental study of Ge nanoislands growth on groove-patterned Si(001) substrate formed by ion-beam-assisted nanoimprint lithography is carried out. Prepatterning procedure includes ion irradiation of Si substrate through imprinted resist mask and subsequent selective etching of irradiated Si domains. It is shown that temperature during ion irradiation affects the location of subsequently grown Ge nanoislands. The effect is interpreted in terms of additional surface tensile strain formed inside grooves by residual irradiation-induced defects. The effect is stronger for cold irradiated samples due to higher density of residual defects.

Probing the three-dimensional strain inhomogeneity and equilibrium elastic properties of single crystal Ni nanowires

We employ three dimensional x-ray coherent diffraction imaging to map the lattice strain distribution, and to probe the elastic properties of a single crystalline Ni (001) nanowire grown vertically on an amorphous SiO2∥Si substrate. The reconstructed density maps show that with increasing wire width, the equilibrium compressive stress in the core region decreases sharply while the surface tensile strain increases, and gradually trends to a nonzero constant. We use the retrieved projection of lattice distortion to predict the Young’s Modulus of the wire based on the elasticity theory.

Harvesting single ferroelectric domain stressed nanoparticles for optical and ferroic applications

We describe techniques to selectively harvest single ferroelectric domain nanoparticles of BaTiO3 as small as 9 nm from a plethora of nanoparticles produced by mechanical grinding. High resolution transmission electron microscopy imaging shows the unidomain atomic structure of the nanoparticles and reveals compressive and tensile surface strains which are attributed to the preservation of ferroelectric behavior in these particles. We demonstrate the positive benefits of using harvested nanoparticles in disparate liquid crystal systems.

Optical anisotropy and strain evolution of GaAs surfaces at the onset of the formation of InAs quantum dots

By using reflectance difference spectroscopy we have studied the in-plane optical anisotropy of GaAs surfaces covered by ultrathin InAs layers. The strain evolution of the GaAs surface with the InAs deposition thickness can be obtained. It is found that the optical anisotropy and the surface tensile strain attain maximum values at the onset of the formation of InAs quantum dots (QDs) and then decrease rapidly as more InAs QDs are formed with the increase of InAs deposition. The origin of the optical anisotropy has been discussed.

Surface strain anomaly induced by the storage and drainage of englacial water in Koryto glacier, Kamchatka, Russia

AbstractTo investigate short-term flow-pattern variations of a temperate glacier, longitudinal surface strain was measured with a wire strainmeter in the ablation area of Koryto glacier, Kamchatka, Russia. Strain-rate anomalies were observed in late summer 2000 that were triggered by a water overflow from a moulin near the measurement site followed by the drainage of accumulated water. The strain event started with (compressive) strain rates of >–10–3 d–1 lasting for 6 hours, which then became tensile. Similar strain-rate variations were observed again on the next day. During the event, basal sliding speed measured at the margin in the lower reach of the glacier fluctuated by about ±50% of the daily mean. Smaller and larger sliding speeds corresponded to the compressive and tensile surface strains, respectively. These measurements suggest that the storage and sudden drainage of water caused spatially non-uniform water-pressure fluctuations along the glacier, changing the sliding regime over short time periods.

Origin of the stability of Ge(105) on si: a new structure model and surface strain relaxation.

The structure of Ge(105)-(1 x 2) grown on Si(105) is examined by scanning tunneling microscopy (STM) and first-principles calculations. The morphology evolution with an increasing amount of Ge deposited documents the existence of a tensile surface strain in Si(105) and its relaxation with increasing coverage of Ge. A detailed analysis of high-resolution STM images and first-principles calculations produce a new stable model for the Ge(105)-(1 x 2) structure formed on the Si(105) surface that includes the existence of surface strain. It corrects the model developed from early observations of the facets of "hut" clusters grown on Si(001).

Functional anatomy of articular cartilage under compressive loading Quantitative aspects of global, local and zonal reactions of the collagenous network with respect to the surface integrity

Objective To assess the influence of local compressive loading on the arrangement of the collagenous fibers in intact articular cartilage. To quantitate the zonal deformation of intact cartilage under load. To analyse the influence of removal of the tangential zone on the load-induced changes.Materials and Methods 380 cylinder shaped cartilage-on-bone samples (d=7mm) were harvested from 20 bovine femoral heads. In 120 of them the tangential zone was removed. All samples were loaded for 20min by 0.42MPa or 0.98MPa. After proteoglycan extraction, fixation in 4% formalin, dehydration by increasing concentrations of acetone, critical point drying, freeze-fracturing and gold-coating the samples were analysed by scanning-electron-microscopy.Results Fiber bulging away from the center of load occurred in an area larger than the directly loaded one and its extent increased parallel to loading (P< 0.01). Crimp was seen only under the indenter and spread with increasing load from the intermediate zone into the tangential zone and radial zone. The absolute height of tangential zone and intermediate zone together remained constant under all loading situations at the costs of the radial zone. All changes due to loading were fully reversible. Removal of the tangential zone reduced the area of bulging (P< 0.01) but markedly increased the amount of crimp. Overall radial strain was not altered, but overall superficial tangential strain was increased by up to 20% (P< 0.01) and high peaks in the local distribution of superficial tensile strain developed.Conclusions The collagenous architecture is a dynamic property of the articular cartilage adapting to its respective loading situation. Crimp reflects local compressive strain. Under compressive loading larger portions of cartilage than the directly loaded areas are functionally included in the process of load transmission. During this process the tangential zone and the intermediate zone form a common functional unit providing a high degree of fiber cross-linkage as a possible mechanism to increase zonal compressive stiffness. Removal of the tangential zone seems to impair distribution of a locally applied compressive load sideways and leads to a reduced cartilage volume included in the process of load transmission. An intact tangential zone contributes to prevent peaks of surface tensile strain.

Deformation and Fracture of Piezoelectric Ceramics(Student Poster Session)

The true stress-strain relation calculated from the relations of load against tensile and compressive surface strains under the Bernoulli's assumption of deformation of beam show nonlinearity and is different between tension and compression. The nonlinearity of the stress and strain relation comes from domain switching induced by external loading. The degree of nonlinearity increased with the easiness of domain switching in bent specimens. The fracture strength in terms of the nominal and true stresses follows the Weibull distribution. The shape parameter takes a large value around, 18 to 22, for PT and PS specimens, while it is the smallest, 7 to 8, for PL specimens. NP specimens take a value in between. The mean strength is the largest for NP specimen and is the lowest for PL specimen. Domain switching during loading will relive local stress concentrations of defects within the material, thus increase the strength and the shape parameter. The change in intensity ratio of the 002 to 200 diffractions can be used to assess the degree of domain switching caused by external straining.

Formation of InAs quantum dots on low-temperature GaAs epi-layer

InAs self-organized quantum dots (QDs) grown on annealed low-temperature GaAs (LT-GaAs) epi-layers and on normal temperature GaAs buffer layers have been compared by transmission electron microscopy (TEM) and photoluminescence (PL) measurements. TEM evidences that self-organized QDs were formed with a smaller size and larger density than that on normal GaAs buffer layers. It is discussed that local tensile surface strain regions that are preferred sites for InAs islands nucleation are increased in the case of the LT-GaAs buffer layers due to exhibiting As precipitates. The PL spectra show a blue-shifted peak energy with narrower linewidth revealing the improvement of optical properties of the QDs grown on LT-GaAs epi-layers. It suggests us a new way to improve the uniformity and change the energy band structure of the InAs self-organized QDs by carefully controlling the surface stress states of the LT-GaAs buffers on which the QDs are formed.

Fibre Waviness Generation and Measurement and Its Effect on Compressive Strength

Artificial fibre waviness was produced by laying up unidirectional carbon fibre-epoxy on a curved plate, and then straightening it before curing. A technique was developed for measuring out-of-plane waviness using a surface displacement transducer mounted on a traversing table. Measurements within the laminate were made by splitting it open along ply interfaces treated with release agent prior to curing. Typical maximum misalignment angles at the centre of a 2 mm thick panel were in the range 0.7 to 1 degree. In-plane waviness data was also generated by splitting the plies along the fibre direction. Tests in a pin-ended buckling rig gave compressive failures with reductions of compressive and tensile surface strain of only 17% and 26%, despite in-plane misalignments of up to 24 degrees in the surface plies.

An energy dissipation-based model for damage stimulated bone adaptation

Based on experimental observations, several researchers have proposed a role for damage processes in stimulating an adaptive response in bone. In the current study we propose a model for bone adaptation based on cyclic energy dissipation as a measure of bone damage creation. By reanalyzing the fatigue data of Pattin et al. (1996), we derive a uniaxial form of the damage based formulation applicable to cortical regions experiencing primarily longitudinal stresses. Because of the experimentally observed difference between damage formation under tension and compression ( Pattin et al., 1996), this formulation naturally predicts a difference in the adaptive response to tensile and compressive loading. This feature distinguishes the new formulation from existing strain energy based adaptation theories which treat tensile and compressive strains identically. Thus, developmental adaptation in response to unequal generation of damage provides one possible explanation for the experimentally observed difference between peak tensile and compressive bone surface strains.

Biaxial Flexing of a Unidirectionally Reinforced Aluminum Composite

Aluminum disks reinforced unidirectionally with silicon carbide con tinuous fiber were supported circumferentially on one side and loaded at the center of the other side with a pin. Maximal principal tensile surface strains were determined during flexing with strain gages. Failure under monotonic loading initiated on the convex side of the disks with the for mation of multiple surface matrix cracks which were parallel to the fibers. These cracks formed soon after matrix yielding which initiated at a strain 0.0015-0.002. On cyclic ten sile biaxial flexing, surface matrix cracking was found to be the main failure mechanism. A limited number of disks failed by fiber cracking. The endurance strain limit for 107 cycles of life was 0.001. This strain is only 11 % of the uniaxial monotonic tensile strain to failure. Ultrasonic velocity scans successfully identified the damage generated during cyclic loading.

Biaxial Flexing of a Fiber Reinforced Aluminum Composite

Disks of silicon carbide continuous fiber reinforced ([0°/90°]4s) aluminum were supported circumferentially on one side and loaded at the center of the other side with a pin. Maxima principal tensile surface strains were determined during flexing with strain gages. Failure under monotonic loading initiated on the convex side of the disks with the for mation of multiple breaks in the first layer of fibers. With further flexing cracking extended to inner fiber layers. Finally, fracture extended through the convex surface layer of the alu minum matrix. On cyclic flexing, fiber cracking was found to be the failure mechanism whenever the cyclic principal surface strain range was 0.0035 or greater. For cyclic strain ranges less than 0.0035, slip bands and cracks were formed in the matrix in addition to the cracks formed in the fibers. The cyclic strain range limit for 10 6 cycles of life was found to approach 0.0015. The latter limit corresponded to a maximum cyclic fiber strain of 0.00132, which is only 15 % of the fiber strain to failure under monotonic uniaxial compos ite loading.

Effect of ion bombardment during deposition on the x-ray microstructure of thin silver films

The effect of argon ion bombardment, during deposition on the microstructure of several tens of nanometers thick Ag films, has been studied. The structure of the Ag films was analyzed by x-ray powder diffraction method. Results show that Ar ion bombardment not only influenced the film growth process but had a significant effect on the structure of the resulting films. In comparison to an evaporated thin Ag film, our films showed much less [111] preferred orientation and a lattice expansion normal to the film surface instead of contraction, with compressive rather than tensile surface strain and plane stress. We also observed much smaller grain sizes, and higher twin fault probabilities, microstrains and dislocation densities. These structural parameters varied systematically with the normalized energy En, that is, the energy deposited by incident energetic Ar+ at the film surface per arriving Ag atom; at first rapidly, then leveling off when En≥42% eV/Ag atom. Preferential orientation is believed to be dependent on film thickness as well as on En. Unlike other parameters, twin fault probability increased to a maximum at En=20 eV/Ag atom and then decreased as En increased further due to self-annealing during deposition.