High Tensile Strain Research Articles

The Influence of Partial Knee Replacement Designs on Tensile Strain at Implant-Bone Interface

Partial knee replacement (PKR) results in fast recovery and good knee mechanics and is ideal to treat medial knee osteoarthritis. Cementless PKR depends on bone growing into the implant surface for long-term fixation. Implant loosening may occur due to high tensile strain resulted from large mechanical loads during rehab exercises. The purpose of this study is to investigate whether external fixations such as superior screw and frontal flange could reduce the tensile strain at the implant-bone interface. Three medial PKRs were designed. The first PKR had no external fixations. A superior screw and a frontal flange were then added to the first PKR to form the second and third PKR designs, respectively. Finite element analysis was performed to examine the tensile strain at the implant-bone interface during weight-bearing exercises. The PKR with no external fixations exhibited high tensile strain at the anterior implant-bone interface. Both the screwed and flanged PKRs effectively reduced the tensile strain at the anterior implant-bone interface. Furthermore, the flanged PKR resulted in a more uniform reduction of the tensile strain than the screwed PKR. In conclusion, external fixations are necessary to alleviate tensile strain at the implant-bone interface during knee rehab exercises.

The Manufacture of Resorbable Suture Material from Magnesium – Drawing and Stranding of Thin Wires

AbstractWith the aid of multiple wire drawing passes, the magnesium alloys ZEK100, MgCa0.8, and AL36 were reduced to monofilament wires possessing diameters between 0.5 and 0.1 mm. These filaments were subsequently twisted into poly‐filament suture material using stranding. In order to analyze the microstructural constituents and the mechanical‐tribological properties, metallographic specimens were prepared and tensile tests were performed on both monofilament as well as poly‐filament wire strands. Appropriate parameters were ascertained for the wire drawing process with regard to forming rate, temperature, and heat treatment. During the investigations, the alloy ZEK100 exhibited particularly interesting mechanical properties which, owing to its high tensile strengths (up to 550 MPa for monofilament) and fracture strains (up to 30% for poly‐filament), are comparable to those of conventional polymer‐based suture materials. In addition to this, integrating a core (internal, individual wire) into the poly‐filament mesh of wire strands represents an interesting alternative for future research in which structures composed of different materials, and the advantages of combining their properties are brought into particular focus.

Nano-structured morphological features of pulsed direct current magnetron sputtered Mo films for photovoltaic applications

Historically, molybdenum thin films have been used as the back contact for Cu(In,Ga)Se 2 based solar cells and as such the properties of these layers play an important role in the overall cell structure. This paper describes the production of molybdenum films using pulsed d.c. magnetron sputtering from compressed molybdenum powder targets. The films were deposited at different substrate temperatures under constant power and constant current modes, and analysed using X-ray diffraction, scanning electron microscopy, atomic force microscopy and four point resistance probe. Mechanical strain and resistivity were found to decrease with substrate temperature together with a shift in the (110) crystallographic plane towards higher diffraction angles. All films were well adhered to the glass substrates irrespective of their high tensile strain. Surface morphology analysis revealed the presence of nano-structured stress relief patterns which can enhance the nucleation sites for subsequent CuInSe 2 deposition. A high-resolution cross sectional image showed the columnar growth of the films. Surface roughness analysis revealed that roughness increased with increase in substrate temperature.

Structural response and strain patterns of isolated ribs under lateral loading

Efforts to mitigate thoracic injury under lateral impact require an understanding of the structural and fracture characteristics of individual ribs under lateral loading. While a number of studies have loaded segments of rib under three-point bending, this study is the first to investigate lateral loading onto entire ribs. Fifteen individual ribs were extracted, positioned upright and a lateral displacement at 1 m/sec was applied. Displacements at the time of fracture were relatively constant across rib levels at 18.3 ± 3.7 mm. Fracture forces ranged from 27 N to 270 N at the anterior extremity and 103 N to 326 N at the posterior extremity; this was also insensitive to rib number. The strain gages indicated that the point immediately opposite the loader on the rib's internal surface experienced the highest tensile strains, while elsewhere the internal surface was in compression and the external surface was in tension. This structural-level rib characterisation can help to better understand the mechanisms of thoracic injury under lateral impact.

Critical tensile and compressive strains for cracking of Al2O3 films grown by atomic layer deposition

Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densities scaled as (1/h)1/2 where h is the Al2O3 ALD film thickness. The fracture toughness for cracking, KIC, of the Al2O3 ALD film was also determined to be KIC = 2.30 MPa m1/2. Thinner Al2O3 ALD film thicknesses also had higher critical strains for cracking from compressive strains. Field-emission scanning electron microscopy (FE-SEM) images revealed that Al2O3 ALD films with thicknesses of 30–50 nm on Teflon fluorinated ethylene propylene (FEP) substrates cracked at a critical compressive strain of ∼1.0%. The critical compressive strain increased to ∼2.0% at a film thickness of ∼20 nm. A comparison of the critical tensile strains on HSPEN substrates and critical compressive strains on Teflon FEP substrates revealed some similarities. The critical strain was ∼1.0% for film thicknesses of 30–50 nm for both tensile and compressive strains. The critical compressive strain then increased more rapidly than the critical tensile strain for thinner films with thicknesses < 30 nm. The high critical tensile and compressive strains for thin Al2O3 ALD films should be very useful for flexible gas diffusion barriers on polymers.

Tight-Binding Calculation of Deformation and Band Gap of Single-Walled Carbon Nanotubes under Axial Tension and Radial Compression

Application of carbon nanotubes (CNTs) to nanometer-scale electronic devices of the next generation is being highly expected owing to their prominent electronic properties and mechanical and chemical stability. Controlling local strain is a key issue to design and realize such devices because of the interplay between mechanical and electronic properties in carbon nanotubes. In this study, we performed semi-empirical tight-binding band calculation of single-walled carbon nanotubes (SWCNTs) with various chiral structures to investigate the deformation behavior and its relation to electronic properties. Firstly, we performed simulation of SWCNTs subject to axial tension, which is one of the simplest deformation modes, to investigate their mechanical properties and change in band gap energies. Pristine SWCNTs can hold high tensile strain. SWCNTs show transition between semiconducting and metallic features during tension, and the transition behavior depends on the chirality of the nanotubes. Secondly, we investigated the mechanical and electronic properties of SWCNTs under radial compression, as it is relatively easy to apply such deformation, for example by moving an AFM tip to a nanotube lying on a plate. SWCNTs are robust under large compression showing no bond breaking or rebonding. The mechanism of the peculiar elastic behavior is discussed. CNTs that have finite band gap energies (semiconducting) at unstrained state show transition to metallic state under radial compression

Cracking behaviour of cast in situ reinforced concrete slabs with control joints

This paper presents the results of a study on the cracking behaviour of cast in situ reinforced concrete slabs with control joints. Material property tests were conducted to establish time-dependent concrete mechanical properties. Cast in situ reinforced concrete slabs with control joints were tested for up to 6 months to study the distribution of concrete cracks and development of concrete strains. A finite element method based model was developed, verified and used for a parametric study. It was found that using control joints can successfully regulate the concrete cracks. The slabs with longer joints suffered less cracks at the edges. The influence of the joint depth was insignificant; however, the joints cut all the way through the slabs caused higher tensile strains than those of shallower cuts. It was also found that the reinforcement ratio and concrete proportion had a significant effect on the cracking of the jointed concrete slabs.

Inhomogeneous strain fields within silicon spheres under the point load test and the strain effect on the quantum valence-bands

This paper presents an exact solution for inhomogeneous strain and stress distributions within silicon spheres under the point load test. The contact problem between the spherical head of the steel cones and the surfaces of the silicon spheres is considered. Displacement functions are introduced in order to uncouple the governing equations. The Fourier–Legendre expansion technique is employed so that all of the boundary conditions can be satisfied exactly. When the isotropic limit is considered, the classical solution by Hiramatsu and Oka [20] is covered as a special case. It was found that the strain distributions are relatively uniform within central part (say r/R<0.6, where r and R are the distance from the center and the radius of the sphere, respectively) of the silicon spheres under the point load test, but very high tensile strain concentrations are usually developed near r/R=0.9. In addition, based on quantum mechanics and energy band theory, the effect of strain on three quantum valence-bands of silicon is analyzed. Numerical results show that the large strain induced at r/R=0.9 of the sphere under the point load test significantly breaks some symmetric property of quantum valence bands of silicon, and has obvious effect on the constant energy surfaces and the conductivity effective masses of heavy hole (HH) band, the light hole (LH) band and the split-off (SO) band, which is closely related to optical and electric property of silicon.

Mechanisms of initial endplate failure in the human vertebral body

Endplate failure occurs frequently in osteoporotic vertebral fractures and may be related to the development of high tensile strain. To determine whether the highest tensile strains in the vertebra occur in the endplates, and whether such high tensile strains are associated with the material behavior of the intervertebral disc, we used micro-CT-based finite element analysis to assess tissue-level strains in 22 elderly human vertebrae (81.5±9.6 years) that were compressed through simulated intervertebral discs. In each vertebra, we compared the highest tensile and compressive strains across the different compartments: endplates, cortical shell, and trabecular bone. The influence of Poisson-type expansion of the disc on the results was determined by compressing the vertebrae a second time in which we suppressed the Poisson expansion. We found that the highest tensile strains occurred within the endplates whereas the highest compressive strains occurred within the trabecular bone. The ratio of strain to assumed tissue-level yield strain was the highest for the endplates, indicating that the endplates had the greatest risk of initial failure. Suppressing the Poisson expansion of the disc decreased the amount of highly tensile-strained tissue in the endplates by 79.4±11.3%. These results indicate that the endplates are at the greatest risk of initial failure due to the development of high tensile strains, and that such high tensile strains are associated with the Poisson expansion of the disc. We conclude that initial failure of the vertebra is associated with high tensile strains in the endplates, which in turn are influenced by the material behavior of the disc.

On the anisotropic wafer curvature of GaN-based heterostructures on Si(1 1 0) substrates grown by MOVPE

We highlight the challenges of GaN growth on (1 1 0)-oriented Si substrates with respect to the substrate-induced anisotropic strain state. A 5:4 lattice matching relationship, which is valid for AlN and Si(1 1 1), is also expected for AlN on Si(1 1 0) along the [1 1 –2 0]AlN/[1 −1 0]Si direction. This reduces the effective lattice mismatch for AlN on Si(1 1 0) along [1 1 –2 0] AlN/[1 −1 0] Si from 23.4% to −1.3% (compressive), while in the [1 −1 0 0] AlN/[0 0 1] Si direction, the mismatch value remains at 0.7% (tensile). The opposite signs of the two mismatch values lead to an anisotropic strain state of the deposited AlN and GaN films, which makes it difficult to balance the tensile strain induced by thermal mismatch. For a simple growth scheme using 1 μm GaN on top of a 40 nm AlN layer, this situation is reflected in an aspherical wafer curvature, anisotropic X-ray diffraction (XRD) Ω scan full width at half maximum (FWHM) values, greater surface roughness and cracking, predominantly occurring parallel to the [1 1 –2 0] direction. The anisotropic XRD FWHM may be explained by a strain-induced anisotropic nucleation mechanism for GaN on AlN. Also, a partial relaxation of the GaN film during growth caused by very high tensile strain along [1 –1 0 0] AlN/[0 0 1] Si is assumed to contribute to the XRD anisotropy. The insertion of an AlN/GaN superlattice structure in between the AlN and GaN films inhibits this relaxation process and leads to a smoother surface morphology with less visible cracks.

Stress in (110)-textured phosphorus-doped polycrystalline diamond studied by Raman and cathodoluminescence spectroscopies

In this work, we investigate the stress developed in phosphorus-doped layers grown on (110)-textured polycrystalline diamond templates. To that end, we follow the shifts of the diamond Raman diffusion and the exciton recombination energies by Raman and cathodoluminescence spectroscopies, respectively. With each approach, a high tensile strain of several gigapascal is evidenced. Moreover, Raman mapping performed in cross section shows (i) at the grain boundaries, a strain in tension that propagates along the growth direction from the template to the deposited layer and (ii) at the center of each grain, a tensile strain of the phosphorus-doped layer with respect to the underlying undoped grain. Concerning the second, we observe also an increase in strain effects at high phosphorus incorporation, together with a structural degradation. The possible origins of such high lattice deformation of phosphorus-doped layers are discussed.

INFLUENCE OF POLY(ETHYLENE GLYCOL) ON PROPERTIES OF PAMPS/PAM DOUBLE NETWORK HYDROGELS

Double network (DN) hydrogels composing of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first network (FN) and poly(acrylamide) (PAM) as the second network (SeN),which were prepared by ultraviolet irradiation polymerization,were modified by poly( ethylene glycol) ( PEG). By adding PEG into single network (SN) hydrogels,many tiny meshes have been made in the network structures; meanwhile the PAM particles of SeN are in different sizes. DN hydrogels modified by PEG become tougher and softer than those without PEG. The swelling behavior was measured gravimetrically at 28℃. The absorbed amount of acrylamide (AM) in SN hydrogels was measured by brominate titration. The structures of different SN hydrogels were successfully characterized by scanning electron microscopy ( SEM). The compressive and tensile properties were examined by using Zwick /Roell tester. The results showed that:this PEG modified DN hydrogels exhibited higher swelling ratio than that of unmodified DN hydrogels,the former was twice times higher than the latter. Interestingly,the volume of DN hydrogels became larger with the gradual increasing amount of PEG in the hydrogels,likewise,the transmittance of DN hydrogels with various PEG amounts became lower. Modified SN hydrogels prefer to absorb AM,because the small meshes,which are in the network of hydrogels,enhance the absorbability of water and AM. Pictures of SEM demonstrate apparently that many small meshes of about 0. 05 ～ 10 μm are in the network structures and the thickness of mesh walls ranges from 0. 02 μm to 0. 2 μm. However,in the unmodified SN hydrogels no obvious meshes were found and the thickness of mesh walls is about 3 μm. Some compressive and tensile properties were enhanced,for example when the PEG = 1. 0 g,the compressive strain of modified DN hydrogels was 90% ,while that of the unmodified ones was 80%. Twice times higher tensile strain than that of unmodified DN hydrogels indicated that modified DN hydrogels had become tougher and softer.

Evaluation of toughness of textile concrete

High Performance Fibre Reinforced Cementitious Composites (HPFRCC) are characterized by a stress–strain response in tension that exhibits strain-hardening behaviour accompanied by propagation of multiple cracks. This process is often referred to as pseudo-ductility due to multiple cracking with relatively large energy absorption capacity. The cracking characteristics are dependent on matrix strength, fibre/matrix bond, fibre volume fraction and the aspect ratio of the fibre used in the composite. The matrix cracking strength and interfacial bond vary with the degree of hydration of cement in the matrix, which is time and environment dependent. This study analyses the multiple cracking patterns formed in weathered Textile Concrete (TC) samples due to direct tensile testing, and links the cracking patterns to the tensile behaviour. The specimens used for the study were thin laminates which were produced by casting six layers of specially made polypropylene (PP) textile in fine-grained mortar. The samples were cured under controlled laboratory conditions for 28 days, and thereafter exposed to different weathering regimes for different periods. The weathered samples were tested in direct tension in a Universal Testing Machine (UTM) over a range of stresses. For all the samples tested, it was observed that the tensile behaviour was characterised by strain hardening and multiple cracking, which gave high tensile strains in excess of 20% at final failure. It was further found that the cracking patterns varied mainly with age, weathering history and stress levels. Other factors that contributed to the cracking characteristics were moisture state of the specimen and the fibre/matrix bonding strength. A strong bond and dense matrix resulted in wide crack spacings compared with samples with a weaker bond which developed closely spaced cracks. A general trend of increasing crack widths and crack spacings with ageing was observed which was accredited to increased hydration accompanied by an increase in fibre/matrix bond strength.

Hybrid Measurement of CT and Strain Distribution of Internal Crack Using Synchrotron High-Energy Monochromatic X-Rays

Using high-energy monochromatic X-rays of energy 66.4keV from the synchrotron radiation source, SPring-8, we have developed a system to perform a hybrid measurement of imaging of cracks and strain distribution around cracks. This system was applied to a fatigue crack made in a round bar made of carbon steel with a diameter of 4 mm. Computed tomography of the specimen gave the three-dimensional shape of a thumb-nail crack. High tensile strain ahead of the crack was measured at the applied maximum stress, while the strain on the crack face was low because of stress relief due to crack opening. The full width at half maximum (FWHM) increased near the crack tip under loading, and then decreased after unloading. The recoverable part of FWHM by unloading was caused by the steep distribution of the applied stress in the vicinity of the crack tip. The FWHM increased by plastic deformation does not change when unloaded. The measured distributions of the lattice strain and FWHM agreed well with those of the elastic and plastic strains calculated by the finite element method, respectively.

Strain analysis of maxillary complete denture with three-dimensional finite element method

The fracture of maxillary complete dentures has been reported as the most common prosthesis failure. The purpose of this study was to evaluate strain distribution in dentures during application of occlusal load with 3-dimensional (3-D) finite element analysis (FEA). A maxillary complete denture was converted into a 3-D numerical model by an advanced topometric sensor digitizer (ATOS). The denture surfaces were scanned with fringes. Ten measurements were made for each scan of the denture in top, left, right, back, and front orientations by tilting the scanning table. The individual scans were merged by the digitizing software into a single image. A haptic device with a freeform system (PHANTOM) was used to create the mucosa in contact with the intaglio surface of the denture model. Supporting bone was then constructed from the mucosa model. The posterior teeth were loaded with an occlusal force of 230 N, and the basal bone was constrained for performing FEA. The highest tensile and compressive strains were found at the incisal and labial frenal notches, respectively. Strains on the intaglio surface of the denture were primarily compressive. The buccal flange exhibited tensile strains in the horizontal direction but compressive strains in the vertical direction. The labial flange showed compressive strains in both directions. The posterior border of the denture flexed away from the mucosa during occlusal loading. Three-dimensional FEA provided different views of strain distribution in the denture and indicated that denture failure was unlikely to occur at the shallow labial frenal notch because the strain is compressive. The high tensile strain concentration at the incisal notch is likely to be the cause of denture fracture during clinical service.

Numerical simulation of mechanisms of deformation, failure and energy dissipation in porous rock media subjected to wave stresses

The pore characteristics, mineral compositions, physical and mechanical properties of the subarkose sandstones were acquired by means of CT scan, X-ray diffraction and physical tests. A few physical models possessing the same pore characteristics and matrix properties but different porosities compared to the natural sandstones were developed. The 3D finite element models of the rock media with varied porosities were established based on the CT image processing of the physical models and the MIMICS software platform. The failure processes of the porous rock media loaded by the split Hopkinson pressure bar (SHPB) were simulated by satisfying the elastic wave propagation theory. The dynamic responses, stress transition, deformation and failure mechanisms of the porous rock media subjected to the wave stresses were analyzed. It is shown that an explicit and quantitative analysis of the stress, strain and deformation and failure mechanisms of porous rocks under the wave stresses can be achieved by using the developed 3D finite element models. With applied wave stresses of certain amplitude and velocity, no evident pore deformation was observed for the rock media with a porosity less than 15%. The deformation is dominantly the combination of microplasticity (shear strain), cracking (tensile strain) of matrix and coalescence of the cracked regions around pores. Shear stresses lead to microplasticity, while tensile stresses result in cracking of the matrix. Cracking and coalescence of the matrix elements in the neighborhood of pores resulted from the high transverse tensile stress or tensile strain which exceeded the threshold values. The simulation results of stress wave propagation, deformation and failure mechanisms and energy dissipation in porous rock media were in good agreement with the physical tests. The present study provides a reference for analyzing the intrinsic mechanisms of the complex dynamic response, stress transit mode, deformation and failure mechanisms and the disaster mechanisms of rock media.

Strained Single-Grain Silicon n- and p-Channel Thin-Film Transistors by Excimer Laser

We have investigated the carrier mobility enhancement of the n- and p-channel single-grain silicon thin-film transistors by the ¿-Czochralski process at a low-temperature process (< 350°C). The high laser energy density near the ablation phenomenon that completely melts the grain filter during the crystallization is responsible for the high tensile strain of the silicon grains, which leads to carrier mobility enhancement.

Direct-bandgap luminescence at room-temperature from highly-strained Germanium nanocrystals

Efficient room-temperature luminescence at optical telecommunication wavelengths and originating from direct band-to-band recombination has been observed in tensile-strained germanium nanocrystals synthesized by mechanical grinding techniques. Selected area electron diffraction, micro-Raman and optical-absorption spectroscopy measurements indicate high tensile-strains while combined photoluminescence spectroscopy, excitation-power evolution and time-resolved measurements suggest direct band-to-band recombination. Such band-engineered germanium nanocrystals offer great possibilities for silicon-photonics integration due to their superb light-emission properties, facile fabrication and compatibility with standard microelectronic processes.

Experimental Study on Fracture Behavior of UHTCC Overlay/Concrete Interfaces under Mixed-Mode Loading

Four-point bending tests are conducted on fiber reinforced cementitious composites (FRCC) overlaid concrete beams with a “T” notch. The objective is to evaluate the fracture behavior of the interface between the FRCC and the concrete substrates. Two types of FRCC overlays are prepared including a traditional steel fiber reinforced concrete (SFRC) composite and an ultra high toughness cementitious composite (UHTCC), which has a very high tensile strain capacity. All two types of FRCC are prepared in two forms: cast on-situ and prefabricated. Test results indicate that, in comparison with others, the prefabricated UHTCC overlay system has exhibited most desirable behavior in terms of the energy absorption in the interface as well as the crack distributions in the overlay, and therefore has a great potential for use in repair of concrete structures.

Functional implications of dicynodont cranial suture morphology

Cranial suture morphology of Lystrosaurus and the generalized dicynodont Oudenodon was investigated to determine the strain environment during mastication, which in turn may indicate a difference in cranial function between the two taxa. Finite element (FE) analysis indicated that less strain accumulated in the cranium of Lystrosaurus during orthal bite simulations than in Oudenodon. Despite the overall difference in strain magnitude, moderate to high FE-predicted strain accumulated in similar areas of the cranium of both taxa. The suture morphology in these cranial regions of Lystrosaurus and Oudenodon was investigated further by examination of histological sections and supplemented by observations of serial sections and computed tomography (CT) scans. The predominant type of strain from selected blocks of finite elements that contain sutures was determined, enabling comparison of suture morphology to strain type. Drawing from strain-suture correlations established in extant taxa, the observed patterns of sutural morphology for both dicynodonts were used to deduce cranial function. The moderate to high compressive and tensile strain experienced by the infraorbital bar, zygomatic arch, and postorbital bar of Oudenodon and Lystrosaurus may have been decreased by small adjustive movements at the scarf sutures in those regions. Disparities in cranial suture morphology between the two taxa may reflect differences in cranial function. For instance, the tongue and groove morphology of the postorbital-parietal suture in Oudenodon could have withstood the higher FE-predicted tensile strain in the posterior skull roof. The scarf premaxilla-nasal suture of Lystrosaurus provided an additional region of sutural mobility in the anterior surface of the snout, suggesting that Lystrosaurus may have employed a different biting regime than Oudenodon. The morphology of several sutures sampled in this study correlated with the FE-predicted strain, although other cranial functional hypotheses remain to be tested.