Decreased Shear Modulus Research Articles

Structure, mechanical properties and thermal decomposition of carbon-alloyed TiAlN thin films: A first-principle study

TiAlCN thin films have been known for their high hardness, favorable toughness and wear properties. Nevertheless, a comprehensive theoretical study conveying the mechanism for the effects of dissolved carbon on the mechanical properties, and thermal stability of TiAlN is still missing. Here, we studied the influence of carbon addition on the structure, modulus and thermal stability of TiAlN by first-principle calculations. The calculated formation energies indicate that carbon preferentially occupies nitrogen site and decreases the solubility of Al in cubic TiN. Furthermore, the enhanced ductility and decreased shear modulus by carbon addition revealed by our calculations, nicely explain the experimentally observed exceptional toughness of TiAlCN. The decomposition enthalpy calculations suggest that c-Ti(C,N) and c-AlN are the most probable decomposition products of TiAlCN. The reduced diffusion barriers of Al, the dominant diffusing atoms, indicate promoted spinodal decomposition process by carbon addition.

Speed-up Measures and Associated Problems for Large-scale DEM-Models

This contribution discusses the possibilities to increase the efficiency of large Discrete Element Method (DEM) simulations. Simulations were conducted to test particle upscaling, decreasing shear modulus and using GPU instead of CPU for the computation. The conducted simulations modelled a simple ore extraction process from a defined outlet of a stope in a cave mine. The analysis is based on the influence of the approaches on the computation speed-up and the accuracy of the result. It was found that the real shear modulus could be decreased in the simulation by a factor of 103 without interfering strongly with the result, provided that the decreased shear modulus is not smaller than 108 Pa. However, a reduction of 102 was found to bring the highest speed-up to the present application.For the particle upscaling in this contribution without parameter calibration, the upscaling factor should not exceed 3. Higher upscaling factors affect the results significantly. However, the flow dynamics was already differing for an upscaling factor of 2, even though the flow zones were comparable. Using a GPU instead of a CPU is only recommended if the simulation contains a high number of particles. The speed-up for a simulation with almost 250,000 particles was over 8, but the advantage diminished for less particles. Furthermore, differences in the results between CPU and GPU computation could be found, which could be a starting point for future work. In summary, this research significantly aids in the development of more efficient DEM simulations for large-scale applications, such as cave mining.

A revisit to the role of Mo in an MP35N superalloy: An experimental and theoretical study

Molybdenum (Mo) has been recognized as an essential alloying element of the MP35N (Co35.4Cr22.9Ni35.5Mo6.2, at.%) superalloy for enhancing strength and corrosion resistance. However, a full understanding of the addition of Mo on microstructure and mechanical properties of the Mo-free parent alloy is lacking. In this work, we consider five (Co37.7Cr24.4Ni37.9)100-xMox (x = 0, 0.7, 2.0, 3.2, and 6.2) alloys, and reveal that yield/tensile strength and ductility are continuously increased for these alloys with increasing Mo content while a single-phase face-centered cubic structure remains unchanged. It is found that strong solid solution strengthening (SSS) is a main domain to the improved yield strength, whereas grain boundaries are found to soften by the Mo addition. The first-principles calculations demonstrate that a severe local lattice distortion contributes to the enhanced SSS, and the grain boundary softening effect is mostly associated with the decreased shear modulus. Both first-principles calculations and scanning transmission electron microscopy observations reveal that the stacking fault energy (SFE) reduces by the Mo addition. The calculated SFE value decreases from 0.4 mJ/m2 to -11.8 mJ/m2 at 0 K as Mo content increases from 0 at.% to 6.2 at.%, and experimentally measured values of SFE at room temperature for both samples are about 18 mJ/m2 and 9 mJ/m2, respectively. The reduction of SFE promoted the generation of stacking faults and deformation twins, which sustain a high strain hardening rate, thus postponing necking instability and enhancing tensile strength and elongation.

Effect of alloy elements on iridium shear modulus by Ab initio analysis.

The effect of the addition of rhodium (Rh), rhenium (Re), tungsten (W), gold (Au), and platinum (Pt) on the shear modulus of face-centered cubic iridium (Ir) was investigated using an ab initio method. The shear modulus was calculated using the second derivative of the strain energy with respect to strain. It was found that both the bulk modulus (G) and the ratio (G/B) between bulk and shear modulus decreased with the addition of elements to the Ir, which meant that all five of these alloy elements lowered the brittleness of the bulk Ir. The decreased shear modulus was the main factor for the lowered brittleness. And the decreasing order of shear modulus in the [112] and [100] crystalline directions was Ir > Rh > Pt > W = Au > Re and Ir > W > Rh > Pt > Au > Re respectively. The reason for the order was both the atomic distance and the bond strength between alloy atoms and Ir atoms. The larger bond strength meant the larger shear modulus, and the smaller atomic distance meant the smaller shear modulus.

In Vitro Effects of Bupivacaine on the Viability and Mechanics of Native and Engineered Cartilage Grafts

Background: Although the toxic effects of bupivacaine on chondrocyte monolayer culture have been well described, its cellular and mechanical effects on native and engineered articular cartilage remain unclear. For the repair of articular cartilage defects, fresh autologous and allogenic cartilage grafts are commonly used, and engineered cell-based therapies are emerging. The outcome of grafting therapies aimed at repairing damaged cartilage relies largely on maintaining proper viability and mechanical suitability of the donor tissues. Purpose: To investigate the in vitro effects of single bupivacaine exposure on the viability and mechanics of 2 cartilage graft types: native articular cartilage and engineered neocartilage. Study Design: Controlled laboratory study. Methods: Articular cartilage explants were harvested from the bovine stifle femoral condyles, and neocartilage constructs were engineered from bovine stifle chondrocytes using the self-assembling process, a scaffold-free approach to engineer cartilage tissue. Both explants and neocartilage were exposed to chondrogenic medium containing a clinically applicable bolus of 0.5%, 0.25%, or 0% (control) bupivacaine for 1 hour, followed by fresh medium wash and exchange. Cell viability and matrix content (collagen and glycosaminoglycan) were assessed at t = 24 hours after treatment, and compressive mechanical properties were assessed with creep indentation testing at t = 5 to 6 days after treatment. Results: Single bupivacaine exposure was chondrotoxic in both explants and neocartilage, with 0.5% bupivacaine causing a significant decrease in chondrocyte viability compared with the control condition (55.0% ± 13.4% vs 71.9% ± 13.5%; P < .001). Bupivacaine had no significant effect on matrix content for either tissue type. There was significant weakening of the mechanical properties in the neocartilage when treated with 0.5% bupivacaine compared with control, with decreased aggregate modulus (415.8 ± 155.1 vs 660.3 ± 145.8 kPa; P = .003), decreased shear modulus (143.2 ± 14.0 vs 266.5 ± 89.2 kPa; P = .002), and increased permeability (14.7 ± 8.1 vs 6.6 ± 1.7 × 10−15 m4/Ns; P = .009). Bupivacaine exposure did not have a significant effect on the mechanical properties of native cartilage explants. Conclusion: Single bupivacaine exposure resulted in significant chondrotoxicity in native explants and neocartilage and significant weakening of mechanical properties of neocartilage. The presence of abundant extracellular matrix does not appear to confer any additional resistance to the toxic effects of bupivacaine. Clinical Relevance: Clinicians should be judicious regarding the use of intra-articular bupivacaine in the setting of articular cartilage repair.

Acute and Prolonged Effects of Stretching on Shear Modulus of the Pectoralis Minor Muscle.

Increased muscle stiffness of the pectoralis minor (PMi) could deteriorate shoulder function. Stretching is useful for maintaining and improving muscle stiffness in rehabilitation and sport practice. However, the acute and prolonged effect of stretching on the PMi muscle stiffness is unclear due to limited methodology for assessing individual muscle stiffness. Using shear wave elastography, we explored the responses of shear modulus to stretching in the PMi over time. The first experiment (n = 20) aimed to clarify the acute change in the shear modulus during stretching. The shear modulus was measured at intervals of 30 s × 10 sets. The second experiment (n = 16) aimed to observe and compare the prolonged effect of different durations of stretching on the shear modulus. Short and long stretching duration groups underwent 30s × 1 set and 30s × 10 sets, respectively. The assessments of shear modulus were conducted before, immediately after, and at 5, 10, and 15 min post-stretching. In experiment I, the shear modulus decreased immediately after a bout (30 s) of stretching (p < 0.001, change: -2.3 kPa, effect size: r = 0.72) and further decreased after 3 repetitions (i.e., 90 s) of stretching (p = 0.03, change: -1.0 kPa, effect size: r = 0.53). In experiment II, the change in the shear modulus after stretching was greater in the long duration group than in the short duration group (p = 0.013, group mean difference: -2.5 kPa, partial η2 = 0.36). The shear modulus of PMi decreased immediately after stretching, and stretching for a long duration was promising to maintain the decreased shear modulus. The acute and prolonged effects on the PMi shear modulus provide information relevant to minimum and persistent stretching time in rehabilitation and sport practice.

Decreased passive muscle stiffness of vastus medialis is associated with poorer quadriceps strength and knee function after anterior cruciate ligament reconstruction

BackgroundMuscle deficits of the quadriceps and hamstrings are common after anterior cruciate ligament reconstruction, and increase the risk of knee reinjury. Muscle stiffness is an important factor for dynamic joint stability. However, the changes in quadriceps and hamstring muscle stiffness and its influence after anterior cruciate ligament reconstruction remain unclear. MethodTwenty-five male subjects with anterior cruciate ligament reconstruction and twenty-one matched healthy subjects participated in this study. The passive muscle stiffness of the quadriceps and hamstrings was assessed by shear modulus using ultrasound shear wave elastography. The isokinetic muscle strengths of the quadriceps and hamstrings were tested. Knee function was evaluated by the International Knee Documentation Committee and Lysholm score. Muscle stiffness was compared between limbs via non-parametric tests. Correlation analysis was used to detect the relationship between muscle stiffness, isokinetic muscle strength and knee functional scores. FindingsThe involved limb exhibited significantly decreased shear modulus in the vastus medialis compared to the dominant limbs(z = −3.585;P = 0.001;ES = 1.13) and non-dominant limbs(z = −3.551;P = 0.002;ES = 1.24) of healthy controls. The shear modulus of ST was also significantly lower in the involved limb when compared with the contralateral limbs(z = −3.996;P < 0.001;ES = 1.33), dominant limbs(z = −4.477;P < 0.001;ES = 1.65) and non-dominant limbs(z = −4.234;P = 0.001;ES = 1.43) of healthy controls. The shear modulus of the vastus medialis was associated with quadriceps peak torque at 60°/s(r = 0.470; p < 0.001) and knee functional score(r = 0.459; p = 0.021). InterpretationThe passive muscle stiffness of the vastus medialis decreased after anterior cruciate ligament reconstruction, which is associated with poorer quadriceps strength and knee function. The effect of modulation of muscle stiffness on improving knee function warrants future investigation.

Effect of anisotropic consolidation and rubber content on dynamic parameters of granulated rubber-sand mixtures

To investigate the shear modulus and damping ratio of granulated rubber-sand mixtures, cyclic triaxial tests were conducted on specimens prepared with different granulated rubber content (by weight) and consolidated under different consolidation ratios. The specimens were then sheared under two cyclic shear strain amplitudes of 0.002 and 0.004 up to 300 cycles. The results show that adding granulated rubber has decreased shear modulus (G) and increased damping ratio (D) under both shear strain amplitudes, but rubber has been helpful in reducing the degradation rate of the shear modulus irrespective of the initial consolidation state. Overall, anisotropic consolidation has had little effects on the variations of shear modulus and damping ratio of granulated rubber-sand mixture (GRSM) compared to clean sand. The sand-rubber mixtures have become more isotropic by increasing the rubber percentage even under anisotropic consolidation. The point that the granulated rubber has significantly contributed to reducing the degradation potential of G with number of cycles makes it attractive in executing backfills and earth structures using rubber-sand mixtures in seismically active zones. The results of this study are also promising in efficient application of granulated rubber-sand mixtures as an isolation system under the foundation of buildings.

Effect of Nb content on the phase composition, densification, microstructure, and mechanical properties of high-entropy boride ceramics

Dense high-entropy (Hf,Zr,Ti,Ta,Nb)B2 ceramics with Nb contents ranging from 0 to 20 at% were produced by a two-step spark plasma sintering process. X-ray diffraction indicated that a single-phase with hexagonal structure was detected in the composition without Nb. In contrast, two phases with the same hexagonal structure, but slightly different lattice parameters were present in compositions containing Nb. The addition of Nb resulted in the presence of a Nb-rich second phase and the amount of the second phase increased as the Nb content increased. The relative densities were all >99.5 %, but decreased from ∼100 % to ∼99.5 % as the Nb content increased from 0 to 20 at%. The average grain size decreased from 13.9 ± 5.5 μm for the composition without Nb additions to 5.2 ± 2.0 μm for the composition containing 20 at% Nb. The reduction of grain size with increasing Nb content was due to the suppression of grain growth by the Nb-rich second phase. The addition of Nb increased Young’s modulus and Vickers hardness, but decreased shear modulus. While some Nb dissolved into the main phase, a Nb-rich second phase was formed in all Nb-containing compositions.

Magnetic resonance elastography of skeletal muscle deep tissue injury.

The current state‐of‐the‐art diagnosis method for deep tissue injury in muscle, a subcategory of pressure ulcers, is palpation. It is recognized that deep tissue injury is frequently preceded by altered biomechanical properties. A quantitative understanding of the changes in biomechanical properties preceding and during deep tissue injury development is therefore highly desired. In this paper we quantified the spatial–temporal changes in mechanical properties upon damage development and recovery in a rat model of deep tissue injury.Deep tissue injury was induced in nine rats by two hours of sustained deformation of the tibialis anterior muscle. Magnetic resonance elastography (MRE), T2‐weighted, and T2‐mapping measurements were performed before, directly after indentation, and at several timepoints during a 14‐day follow‐up.The results revealed a local hotspot of elevated shear modulus (from 3.30 ± 0.14 kPa before to 4.22 ± 0.90 kPa after) near the center of deformation at Day 0, whereas the T2 was elevated in a larger area. During recovery there was a clear difference in the time course of the shear modulus and T2. Whereas T2 showed a gradual normalization towards baseline, the shear modulus dropped below baseline from Day 3 up to Day 10 (from 3.29 ± 0.07 kPa before to 2.68 ± 0.23 kPa at Day 10, P < 0.001), followed by a normalization at Day 14.In conclusion, we found an initial increase in shear modulus directly after two hours of damage‐inducing deformation, which was followed by decreased shear modulus from Day 3 up to Day 10, and subsequent normalization. The lower shear modulus originates from the moderate to severe degeneration of the muscle. MRE stiffness values were affected in a smaller area as compared with T2. Since T2 elevation is related to edema, distributing along the muscle fibers proximally and distally from the injury, we suggest that MRE is more specific than T2 for localization of the actual damaged area.

Structural, elastic and electronic properties of Cr2N: A first-principles study

The superior hardness of hexagonal Cr2N makes it potential applications as hard film. In this paper, first principles calculations are firstly made to investigate the structural, elastic and electronic properties of Cr2N. The site preferences of N in Cr2N crystal are evaluated by the formation energies of various configurations. The theoretical elastic properties of Cr2N are obtained and show close relation with the N occupation. The N occupations of 1a and 2d sites enable Cr2N the enhanced stability and increased elastic modulus and shear modulus. The N occupation at 2c sites shows a softening effect indicated by decreased shear modulus. The analysis on the density of states clarifies the variations of the stability and elastic properties of Cr2N.

A novel cosmetic approach to treat thinning hair

Many of today's treatments associated with 'thinning hair', such as female pattern hair loss and telogen effluvium, are focused on two of the key aspects of the condition. Over-the-counter or prescription medications are often focused on improving scalp hair density while high-quality cosmetic products work to prevent further hair damage and minimize mid-fibre breakage. Fibre diameter is another key contributor to thinning hair, but it is less often the focus of medical or cosmetic treatments. To examine the ability of a novel leave-on technology combination [caffeine, niacinamide, panthenol, dimethicone and an acrylate polymer (CNPDA)] to affect the diameter and behaviour of individual terminal scalp hair fibres as a new approach to counteract decreasing fibre diameters. Testing methodology included fibre diameter measures via laser scan micrometer, assessment of fibre mechanical and behavioural properties via tensile break stress and torsion pendulum testing, and mechanistic studies including cryoscanning electron microscopy and autoradiographic analysis. CNPDA significantly increased the diameter of individual, existing terminal scalp hair fibres by 2-5 μm, which yields an increase in the cross-sectional area of approximately 10%. Beyond the diameter increase, the CNPDA-thickened fibres demonstrated the altered mechanical properties characteristic of thicker fibres: increased suppleness/pliability (decreased shear modulus) and better ability to withstand force without breaking (increased break stress). Although cosmetic treatments will not reverse the condition, this new approach may help to mitigate the effects of thinning hair.

Dynamics of Flow in a Mechanical Heart Valve: The Role of Leaflet Inertia and Leaflet Compliance

In this work, we examine the dynamics of fluid flow in a mechanical heart valve when the solid inertia and leaflet compliance are important. The fluid is incompressible and Newtonian, and the leaflet is an incompressible neo-Hookean material. In the case of an inertialess leaflet, we find that the maximum valve opening angle and the time that the valve remains closed increase as the shear modulus of the leaflet decreases. More importantly, the regurgitant volume decreases with decreasing shear modulus. When we examined the forces exerted on the leaflet, we found that the downward motion of the leaflet is initiated by a vertical force exerted on its right side and, later on, by a vertical force exerted on the top side of the leaflet. In the case of solid inertia, we find that the maximum valve opening angle and the regurgitant volume are larger than in the case of an inertialess leaflet. These results highlight the importance of solid compliance in the dynamics of blood flow in a mechanical heart valve. More importantly, they indicate that mechanical heart valves with compliant leaflets may have smaller regurgitant volumes and smaller shear stresses than the ones with rigid leaflets.

A single cell model for pretreatment of wood by microwave explosion

Abstract A theoretical model was developed to better understand the process of microwave explosion treatment of wood cells. The cell expansion and critical conditions concerning pressure and temperature of ray parenchyma cells in Eucalyptus urophylla were simulated during microwave pretreatment. The results indicate that longitudinal and circumferential stresses were generated in the cell walls owing to the internal steam pressure during extensive microwave treatment. The circumferential stress is twice as high as the longitudinal stress. The pressure difference reaches its maximum value of 0.84 MPa when the extension ratio is 1.20 for the longitudinal direction and 1.62 for the circumferential direction. The maximum pressure difference at the theoretical yielding point is the critical pressure difference that can eventually rupture the ray cell. The critical pressure difference decreases with increasing cell radius and decreasing shear modulus in the cell wall. This simulated result provides useful information to modify wood at the level of ray parenchyma cells.

Green's functions for vertical point load on an elastic half-space with depth-degrading stiffness

The response of an elastic, vertically non-homogeneous half-space to a time-harmonic surface point load is studied. The non-homogeneity is defined by a function that may describe both increasing and decreasing shear modulus with depth. The solution for the latter is obtained in the paper by simple transformations from the previously derived one for a half-space with increasing shear modulus with depth. The analysis shows that cut-off frequencies for the SV/P surface wave may occur. Graphs for the variation of the complex valued displacement field with distance from the source and frequency are presented for selected values of the non-homogeneity parameters.

Disorder effects on the strain response of model polymer networks

Molecular dynamics simulations are used to investigate polymer networks made by either end-linking or randomly crosslinking a melt of linear precursor chains. The resulting network structures are very different, since end-linking leads to nearly ideal monodisperse networks, while random crosslinking leads to polydisperse networks, characterized by an exponential strand length distribution. Networks with average strand length 20 and 100 were generated. These networks were used to study the effects of disorder in the network connectivity on observables averaged either over the entire network or selected sub-structures. Heterogeneities in the randomly crosslinked networks cause significant differences in the localization of monomers, however, neither the localization of crosslinks nor the microscopic strain response are significantly affected. Compared to end-linked networks, randomly crosslinked networks have a slightly increased tube diameter, and as a result a slightly decreased shear modulus, but otherwise identical stress–strain behavior. For the investigated systems, we conclude that the microscopic strain response, tube diameter, and stress–strain relation are all insensitive to the heterogeneities due to the linking process by which the network were made.

Natural-fibre-reinforced polyurethane microfoams

Polyurethane-based composites reinforced with woven flax and jute fabrics were prepared with an evenly distributed microvoid foam structure. The relationship between the resin-filled grade and the microvoid content and the density was described. The influence of the type of reinforcing fibre, fibre and microvoid content on the mechanical properties was studied. The investigation results for the static mechanical properties of the composites were described by approximate formulae. It was found that the specific data were only slightly dependent on microvoid content. Increasing the fibre content induces an increase in the shear modulus and impact strength. However, increasing the microvoid content in the matrix results in a decreased shear modulus and impact strength. The woven flax fibre results in composites with better mechanical strength than the woven jute fibre composites.

The creep behavior of glass-ionomer restorative materials

The creep of microspecimens of five glass-ionomer filling materials and one glass-ionomer-cermet cement was studied by means of a torsional creep apparatus. The glass-ionomer specimens were aged one week and conditioned in 37°C water. Shear stress of 2.47× 10 −4 N.m. was maintained for three h, and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50°C. The effect of temperature increase was studied. All the glass ionomers exhibited linear visco-elastic behavior at low deformations. Their shear moduli and resistance to creep were similar to those of some composites measured by the same method. The increase of temperature influenced the creep behavior and moduli of the materials (i.e., increased creep and residual strains and decreased shear modulus). Although the applied torque was very small. there was permanent deformation, the result of viscous flow in all experiments which was more pronounced at 50°C.

Analysis of the interfacial stresses produced by a pile-up of discrete edge dislocations in two phase materials

The local stresses associated with a pile-up of discrete edge dislocations against a welded interface at a second phase have been calculated using the elasticity solution of Dundurs. The calculations permit a study of the effects of applied stress, pile-up length, and the elastic properties of the two phases on the distribution of dislocations in the pile-up and on the stresses at the interface. The equilibrium positions of the dislocations and their discrete contributions to the stresses at the interface have been investigated for cases in which the shear modulus of the second phase is greater than and less than (or equal to) that of the matrix. For the latter case, the leading dislocation is assumed to be locked at the interface. The local stress is found to increase with applied stress and pile-up length, as expected. For a given applied stress and pile-up length, the stresses at the interface increase with decreasing shear modulus of the second phase and also depend on the Poisson's ratios of the two phases. The analysis is used to study the effects of microstructure on the plastic deformation of two phase alloys.