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The main objective of this work is to evaluate the mechanical and thermal strength of a recently developed composite made of Cissus quadrangularis fiber coupled with Polylacticacid (PLA) in comparison to other natural fibers. This study investigated three different fiber and PLA compositions—20%, 30%, and 40%, respectively used to produce a composite. In contrast, another composite with the same volume percentage was created using calcium hydroxide Ca(OH)2 to coat the fibers in order to alter their microcrystalline structure and enhance their mechanical properties. The composite was created using an injection molding procedure. Tests were performed to assess the improved properties. According to a preliminary study, the mechanical characteristics of PLA combined with treated Cissus quadrangularis fiber are increased when compared to PLA coupled with untreated Cissus quadrangularis fiber and neat PLA. Calcium hydroxide acted as a binding agent in fiber to enhance stress transmission in the matrix, increasing tensile and flexural modulus as well as toughness elongation. Further DSC analysis showed that the inclusion of the preceding components increased the glass transition temperature and melting temperature. The temperature at the beginning of deflection has risen as a result of showing how increasing HDT, fiber–matrix adhesion, and fiber content are related. The morphological analysis was performed on both untreated and chemical-treated fiber composites by using an optical microscope to see the interaction with the fiber matrix. [ABSTRACT FROM AUTHOR]

• A thermodynamic model is developed to predict the property of stochastic heterogeneous material. • Metal wires with various gauge length are tensile tested to verify the feasibility of the model. • With decreasing gauge length, the failure strain decreases and fracture stress almost unchanged. • The newly developed random field model can well demonstrate the origination of size effect. • Size effect originates from the intrinsic stochasticity and correlation of mechanical property. Materials are intrinsic stochastic heterogeneity regardless of their natural or artificial origin. Traditional models for predicting mechanical properties of materials typically involve homogenization, which exhibits certain limitations in practical applications, such as investigating the size effect in stress–strain relationships. In this study, a random field thermodynamic theory for predicting the mechanical properties of stochastic heterogeneous materials was proposed, and its applicability and reliability were verified by testing hard-drawn 304 stainless-steel wires with gauge lengths of 10–500 mm. In these wires composed of the lamellar martensite with a thickness of ∼47.1 nm, it is found that failure strains decreased significantly with increasing gauge length, whereas fracture stresses show little dependence on the gauge length leading to a great increase of the effective modulus. Digital image correlation investigations revealed a significant strain heterogeneity during the tensile process, even at the elastic deformation stage. Nanoindentation tests show the non-uniformly distributed reduced modulus and hardness, which can be attributed to the intrinsic stochastic heterogeneity of materials. Taking Young's modulus as a one-dimensional stationary random field along the longitudinal direction, our random field model can well demonstrate the variation of failure strain and effective modulus with changing gauge lengths. The size effect on the macroscopic mechanical properties mainly originated from the microscopic mechanical property correlation of different points within the materials. These findings could provide new insights into the size effect on the mechanical properties of materials. [ABSTRACT FROM AUTHOR]

Highlights • A theoretical indentation model applicable to film/substrate systems with large modulus ratios (E f /E s = 102–105) is established. • A new convenient method for measuring the modulus of nanofilm with limited thickness by indentation on hard film/soft substrate system is proposed. • Compared with the free-standing indentation test or bulge test, this method is more convenient and cheaper. • The effectiveness of the model and method was verified by experiments and simulations. Abstract Two-dimensional (2D) materials have received extensive attention due to their excellent physical and chemical properties, whose mechanical properties play critical roles in their applications. In this paper, a new convenient method for measuring the modulus of nanofilm by indentation on hard film/soft substrate system is proposed. In order to verify the correctness of the new method, the graphene oxide (GO) nanofilm deposited on polydimethylsiloxane (PDMS) is tested. The modulus of the GO nanofilm is measured as 60.39 ± 7.82 GPa, which is consistent with the modulus measured by previous researches. Finally, the finite element method (FEM) is used to investigate the effectiveness of the new method and to evaluate its error sensitivity to the indenter size, film radius, and the surface roughness. The results show that this method can accurately measure the modulus of nanofilm through the indentation response of the hard film/soft substrate system. Compared with the free-standing indentation test, the method proposed by us eliminates the disadvantages of boundary adhesion and has the advantages of simple sample preparation, easy operation, and high success rate. [ABSTRACT FROM AUTHOR]

Mechanical properties and lithiation-induced stress are crucial to the performance and durability of lithium-ion batteries. Here, we report the evolution of elastic modulus and stress in a silicon/polyvinylidene fluoride (PVDF) composite electrode coated on a copper foil, along with a model for analyzing the large change in the radius of curvature of the composite electrode/copper foil cantilever. The radius of curvature of the cantilever is captured by a video camera during lithiation/delithiation. The elastic modulus of the composite electrode decreases from about 0.64 GPa to 0.18 GPa during lithiation. It decreases further to about 0.10 GPa after delithiation, which is caused by the fracture of the electrode. The magnitude of the compressive stress increases lineally during lithiation and decreases suddenly to reach a steady state value during delithiation. [ABSTRACT FROM AUTHOR]

Background: The purpose of this study was to compare the frequency-dependent viscoelastic properties of human and bovine cartilage. Methods: Full-depth cartilage specimens were extracted from bovine and human femoral heads. Using dynamic mechanical analysis, the viscoelastic properties of eight bovine and six human specimens were measured over the frequency range 1 Hz to 88 Hz. Significant differences between bovine and human cartilage viscoelastic properties were assessed using a Mann–Whitney test (p < 0.05). Results: Throughout the range of frequencies tested and for both species, the storage modulus was greater than the loss modulus and both were frequency-dependent. The storage and loss moduli of all human and bovine cartilage specimens presented a logarithmic relationship with respect to frequency. The mean human storage modulus ranged from 31.9 MPa to 43.3 MPa, while the mean bovine storage modulus ranged from 54.0 MPa to 80. 5 MPa; bovine storage moduli were 1.7 to 1.9 times greater than the human modulus. Similarly, the loss modulus of bovine cartilage was 2.0 to 2.1 times greater than human. The mean human loss modulus ranged from 5.3 MPa to 8.5 MPa while bovine moduli ranged from 10.6 MPa to 18.1 MPa. Conclusion: Frequency-dependent viscoelastic trends of bovine articular cartilage were consistent with those of human articular cartilage; this includes a similar frequency dependency and high-frequency plateau. Bovine cartilage was, however, ‘stiffer’ than human by a factor of approximately 2. With these provisos, bovine articular cartilage may be a suitable dynamic model for human articular cartilage. [ABSTRACT FROM AUTHOR]

An increase in environmental concern invites the development new eco friendly materials having light weight and superior mechanical performance. In this connection an attempt is made to manufacture composites reinforced with long time exposed dora hemp fibre at ambient conditions into the unsaturated polyester resin. The fabricated composite specimens are processed at P1, P2 and P3 conditions to assess their mechanical performance as per ASTM procedures. Out of all the composites investigated in the present work the dora hemp composites at P2 have shown good tensile and flexural properties, whereas the highest impact strength is achieved for the composites at P1. Hence this class of natural fibre composites is suitable for making automobile components after thorough investigation of necessary parameters. [ABSTRACT FROM AUTHOR]

Abstract: One of the crucial characteristics of a porous medium is its relative density ρ *, i.e. the volume fraction of the solid. For example, in low density foams (ρ * <0.1) the macroscopic material properties depend on the foam geometry only through the relative density. The relative density of nanoporous (NP) metal foams synthesized by dealloying is typically in the range ρ * ⩾0.4. This places NP metal foams in a previously unexplored parameter regime and necessitates reexamination of scaling laws derived for low density foams. In this work we demonstrate that the modulus of NP metal foams does not exhibit a clear correlation with the relative density. We trace this apparent disagreement with existing scaling laws to the agglomeration of mass in the junctions. We then derive and verify a new scaling relationship for the dependence of relative density and relative modulus on the geometric parameters such as strut thickness, length and junction size. We find good agreement between our model and experimental measurements for single crystal gold NP foams with large junction sizes. In contrast, polycrystalline NP platinum with nanosized grains within the struts shows an enhancement in the modulus that cannot be attributed to the foam geometry only. Based on this analysis, we infer a more than an order of magnitude enhancement of the modulus of the nanograined Pt struts compared to bulk platinum. [Copyright &y& Elsevier]

Abstract: Hydrogels prepared from poly-(ethylene glycol) (PEG) have been used in a variety of studies of cartilage tissue engineering. Such hydrogels may also be useful as a tunable mechanical material for cartilage repair. Previous studies have characterized the chemical and mechanical properties of PEG-based hydrogels, as modulated by precursor molecular weight and concentration. Cartilage mechanical properties vary substantially, with maturation, with depth from the articular surface, in health and disease, and in compression and tension. We hypothesized that PEG hydrogels could mimic a broad range of the compressive and tensile mechanical properties of articular cartilage. The objective of this study was to characterize the mechanical properties of PEG hydrogels over a broad range and with reference to articular cartilage. In particular, we assessed the effects of PEG precursor molecular weight (508 Da, 3.4 kDa, 6 kDa, and 10 kDa) and concentration (10–40%) on swelling property, equilibrium confined compressive modulus (H A0), compressive dynamic stiffness, and hydraulic permeability (k p0) of PEG hydrogels in static/dynamic confined compression tests, and equilibrium tensile modulus (E ten) in tension tests. As molecular weight of PEG decreased and concentration increased, hydrogels exhibited a decrease in swelling ratio (31.5–2.2), an increase in H A0 (0.01–2.46 MPa) and E ten (0.02–3.5 MPa), an increase in dynamic compressive stiffness (0.055–42.9 MPa), and a decrease in k p0 (1.2 × 10−15 to 8.5 × 10−15 m2/(Pa s)). The frequency-dependence of dynamic compressive stiffness amplitude and phase, as well as the strain-dependence of permeability, were typical of the time- and strain-dependent mechanical behavior of articular cartilage. H A0 and E ten were positively correlated with the final PEG concentration, accounting for swelling. These results indicate that PEG hydrogels can be prepared to mimic many of the static and dynamic mechanical properties of articular cartilage. [Copyright &y& Elsevier]

Abstract: Stress and plastic deformation analyses of catalyst layer have been conducted after experimentally investigating its mechanical properties at nano-scale. Interestingly, catalyst layer is found to have varying mechanical properties as a function of depth and therefore it is classified under graded material. Effect of gradation in catalyst layer on interfacial strength between membrane and catalyst layer is explained with the aid of numerical simulations. Stress redistribution near interface line is observed in graded model, while stresses are found to have concentrated at critical locations throughout the discrete model. However, it is outlined from this study that the gradation in catalyst layer leads to greater amount of plastic energy dissipation—an indication of enhanced ductility. An experimental coupled numerical approach is presented to characterize the effect of transitional variations of mechanical properties in catalyst layer on the interfacial line and membrane. [Copyright &y& Elsevier]

The elastic modulus and failure behavior of poly(urea-formaldehyde) shelled microcapsules were determined through single-capsule compression tests. Capsules were tested both dry and immersed in a fluid isotonic with the encapsulent. The testing of capsules immersed in a fluid had little influence on mechanical behavior in the elastic regime. Elastic modulus of the capsule shell wall was extracted by comparison with a shell theory model for the compression of a fluid filled microcapsule. Average capsule shell wall modulus was 3.7 GPa, regardless of whether the capsule was tested immersed or dry. Microcapsule diameter was found to have a significant effect on failure strength, with smaller capsules sustaining higher loads before failure. Capsule size had no effect on the modulus value determined from comparison with theory. [ABSTRACT FROM AUTHOR]

In materials science and engineering, a significant amount of research has been carried out using indentation techniques in order to characterize the mechanical properties and microstructure of a broad range of natural and engineered materials. However, there are many unresearched or partly researched areas, such as, for example, the investigation of the shape of the indentation load–displacement curve, the associated mechanism in porous materials with clastic texture, and the influence of the texture on the constitutive behavior of the materials. In the present study, nanoindentation is employed in the analysis of the mechanical behavior of a benchmark material composed of plaster of Paris, which represents a brand of highly porous-clastic materials with a complex structure; such materials may find many applications in medicine, production industry, and energy sectors. The focus of the study is directed at the examination of the influence of the porous structure on the load–displacement response in loading and unloading phases based on nanoindentation experiments, as well as the variation with repeating the indentation in already indented locations. Events such as pop-in in the loading phase and bowing out and elbowing in the unloading phase of a given nanoindentation test are studied. Modulus, hardness, and the elastic stiffness values were additionally examined. The repeated indentation tests provided validations of various mechanisms in the loading and unloading phases of the indentation tests. The results from this study provide some fundamental insights into the interpretation of the nanoindentation behavior and the viscoelastic nature of porous-clastic materials. Some insights on the influence of indentation spacing to depth ratio were also obtained, providing scope for further studies. [ABSTRACT FROM AUTHOR]

The longevity of indirect restorations is primarily determined by the appropriate selection of the luting material. The function of a luting material is to seal the restoration and hold it in place for the time required for service. The mechanical behavior of luting materials and in particular their aging behavior, therefore, play a decisive role. The study provides a comparative analysis of the static and dynamic mechanical behavior of the most commonly used luting material categories—zinc phosphate cement, glass–ionomer cement, resin-modified glass–ionomer cement, resin-based composites, and self-adhesive resin-based composites—and their aging behavior. It also takes into account that luting materials are viscoelastic materials, i.e., materials that respond to external loading in a way that lies between an elastic solid and a viscous liquid. Flexural strength and modulus were determined in a three-point bending test followed by fractography analysis. The quasi-static and viscoelastic behavior was analyzed by a depth-sensing indentation test provided with a dynamic mechanical analysis (DMA) module at 20 different frequencies (1–50 Hz). The fracture toughness was evaluated in a notchless triangular prism (NTP) test. Material type exhibits the strongest influence on all measured properties, while the effect of aging becomes more evident in the material reliability. The variation of the viscoelastic parameters with aging reflects cement maturation or polymer plasticization. [ABSTRACT FROM AUTHOR]

Energy storage and dissipation by composite materials are important design parameters for sensors and other devices. While polymeric materials can reversibly store energy by decreased chain randomness (entropic loss) they fail to be able to dissipate energy effectively and ultimately fail due to fatigue and molecular chain breakage. In contrast, composite tissues, such as muscle and tendon complexes, store and dissipate energy through entropic changes in collagen (energy storage) and viscous losses (energy dissipation) by muscle fibers or through fluid flow of the interfibrillar matrix. In this paper we review the molecular basis for energy storage and dissipation by natural composite materials in an effort to aid in the development of improved substrates for sensors, implants and other commercial devices. In addition, we introduce vibrational optical coherence tomography, a new technique that can be used to follow energy storage and dissipation by composite materials without physically touching them. [ABSTRACT FROM AUTHOR]