Compressive and Tensile Elastic Properties of Concrete: Empirical Factors in Span Reinforced Structures Design

Concretes with the same strength can have various deformability that influences span structures deflection. In addition, a significant factor is the non-linear deformation of concrete dependence on the load. The main deformability parameter of concrete is the instantaneous modulus of elasticity. This research aims to evaluate the relation of concrete compressive and tensile elastic properties testing. The beam samples at 80 × 140 × 1400 cm with one rod Ø8 composite or Ø10 steel reinforcement were experimentally tested. It was shown that instantaneous elastic deformations under compression are much lower than tensile. Prolonged elastic deformations under compression are close to tensile. It results in compressive elasticity modulus exceeding the tensile. The relation between these moduli is proposed. The relation provides operative elasticity modulus testing by the bending tensile method. The elasticity modulus’s evaluation for the reinforced span structures could be based only on the bending testing results. A 10% elasticity modulus increase, which seems not significant, increases at 30–40% the stress of the reinforced span structures under load and 30% increases the cracking point stress.

Can UVA-light-activated riboflavin-induced collagen crosslinking be transferred from ophthalmology to spine surgery? A feasibility study on bovine intervertebral disc

Background Collagen cross-links contribute to the mechanical resilience of the intervertebral disc (IVD). UVA-light-activated riboflavin-induced collagen crosslinking (UVA-CXL) is a well-established and effective ophthalmological intervention that increases the mechanical rigidity of the collagen-rich corneal matrix in Keratoconus. This study explores the feasibility, safety and efficacy of translating this intervention in reinforcing the IVD. Methods Annulus fibrosus (AF) cells were isolated from bovine IVDs and treated with different combinations of riboflavin (RF) concentrations (0.05–8 mM) and UVA light intensities (0.3–4 mW/cm2). Metabolic activity (resazurin assay), cell viability (TUNEL assay), and gene expression of apoptosis regulators C-FOS and PT5 were assessed immediately and 24 hours after treatment. Biomechanical effects of UVA-CXL on IVDs were measured by indentation analysis of changes in the instantaneous modulus and by peel-force delamination strength analysis of the AF prior and after treatment. Results Different intensities of UVA did not impair the metabolic activity of AF cells. However, RF affected metabolic activity (p < 0.001). PT53 expression was similar in all RF conditions tested while C-FOS expression decreased 24 hours after treatment. Twenty-four hours after treatment, no apoptotic cells were observed in any condition tested. Biomechanical characterizations showed a significant increase in the annular peel strength of the UVA-CXL group, when compared to controls of UVA and RF alone (p < 0.05). UVA-CXL treated IVDs showed up to 152% higher (p < 0.001) instantaneous modulus values compared to the untreated control. Conclusion This is the first study on UVA-CXL treatment of IVD. It induced significantly increased delamination strength and instantaneous modulus indentation values in intact IVD samples in a structure–function relationship. RF concentrations and UVA intensities utilized in ophthalmological clinical protocols were well tolerated by the AF cells. Our findings suggest that UVA-CXL may be a promising tool to reinforce the IVD matrix.

Correlation of Biomechanical Alterations under Gonarthritis between Overlying Menisci and Articular Cartilage

Just like menisci, articular cartilage is exposed to constant and varying stresses. Injuries to the meniscus are associated with the development of gonarthritis. Both the articular cartilage and the menisci are subject to structural changes under gonarthritis. The aim of this study was to investigate biomechanical alterations in articular cartilage and the menisci under gonarthritis by applying an indentation method. The study assessed 11 menisci from body donors as controls and 21 menisci from patients with severe gonarthritis. For the simultaneous examination of the articular cartilage and the menisci, we only tested the joint surfaces of the tibial plateau covered by the corresponding menisci. Over the posterior horn of the meniscus, the maximum applied load—the highest load registered by the load cell—of the arthritic samples of 0.02 ± 0.02 N was significantly greater (p = 0.04) than the maximum applied load of the arthritis-free samples of 0.01 ± 0.01 N. The instantaneous modulus (IM) at the center of the arthritic cartilage covered by the meniscus with 3.5 ± 2.02 MPa was significantly smaller than the IM of the arthritis-free samples with 5.17 ± 1.88 MPa (p = 0.04). No significant difference was found in the thickness of the meniscus-covered articular cartilage between the arthritic and arthritis-free samples. Significant correlations between the articular cartilage and the corresponding menisci were not observed at any point. In this study, the biomechanical changes associated with gonarthritis affected the posterior horn of the meniscus and the mid region of the meniscus-covered articular cartilage. The assessment of cartilage thickness as a structural characteristic of osteoarthritis may be misleading with regard to the interpretation of articular cartilage’s biomechanical properties.

MATHEMATICAL SIMULATION OF KNIFE PROFILE RESISTANCE FORCE DURING FISH CUTTING

The article focuses on studying the fish cutting process and modeling forces of harmful resistance. The fish muscular tissue rheological properties are described by a Maxwell-Thomson model. The conditions of constrained compression of the material across the width and the absence of constrained compression in the direction of movement of the knife are accepted. On the basis of the energy approach, the profile resistance force of the double-edged knife has been interpreted as deformational force of the friction at the macroscopic scale level, provided that the surface of the faces is smooth. The mathematical models for dimensional and dimensionless profile resistance forces of the knife without side edges have been developed. The dependence of the dimensional force on the sharpening angles, knife thickness, rheological properties and cutting speed has been established. The dependence of the dimensionless force on the dimensionless cutting speed and measure of the muscle tissue elasticity has been shown. The profile resistance forces of flat-back knife and double-edged knives have been analyzed. With sharpening angle of back edges = 5°; 10°; 20°; 50°, force maximums are 0.317; 0.306; 0.288; 0.274, respectively. When the values of instantaneous modulus of elasticity 1.5·105; 2.0·105; 2.5·105; 3.0·105 N/m2, the maximums of the specified force are 0.310; 0.411; 0.513; 0.614 N, respectively. With the values of elasticity = 4; 7; 11; 15, dimensionless force maximums of flat-back knife are 1.959; 3.166; 4.774; 6.381 and without side edges - 1.193; 1.864; 2.764; 3.663, respectively.

Viscoelastic Responses of Inorganic-Oranic Hybrids Polymers

ABSTRACTThe properties of nano-structured plastics are determined by complex relationships between the type and size of the nano-reinforcement, the interface and chemical interaction between the nano-reinforcement and the polymeric chain, along with macroscopic processing and microstructural effects. In this paper we investigated the thermal and viscoelastic property enhancement on crosslinked epoxy using two types of nano-reinforcement, namely organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS) macromers. Glass transitions of these nano-composites were studied using differential scanning calorimetry. Small strain stress relaxation under uniaxial deformation was examined to provide insights into the timedependent viscoelastic behavior of these nano-composites. Since the size of POSS macromer is comparable to the distance between molecular junctions, hence as we increase the amount of POSS macromers, the glass transition temperature, Tg, as observed by DSC increase. However for epoxy network reinforced with clay, we did not observe any effect on the Tg due to the presence of clay reinforcements. In small strain stress relaxation experiments, both types of reinforcement provided some enhancement in creep resistance, namely the characteristic relaxation time as determined using a stretched exponential relaxation function increased with the addition of reinforcements. However, due to different reinforcement mechanisms, enhancement in the instantaneous modulus was observed for clay-reinforced epoxies, while the instantaneous modulus was not effected in POSS-epoxy nano-composites.

Biomechanical Tissue Properties as an Indicator of Organ Vitality Prior to Transplantations

An organ's vitality prior to transplatation can be evaluated by analysis of its mechanical properties. A new apparatus was designed to measure these properties. The organ to be tested is placed in a reservoir with saline and submitted to the load of a cylindrical element. The load is applied in a stepwise mode and results in a small local deformation of the organ. This deformation is identical to the displacement of the cylinder and is measured as a function of time. This is compared to a theoretical analysis of the deformation of a viscoelastic halfspace. This theory was used to interpret the results of experiments which were carried out on eight rabbit kidneys. The instantaneous modulus of elasticity reaches a maximum within 15 minutes, then decreases and reaches a steady state after 30 minutes of warm ischemia. The method is easy to apply and appears to be useful for the quantification of an organ's vitality and in particular recognizes the level of the organ's edema before transplantation