Numerical analysis of bending property of bi-modulus materials and a new method for measurement of tensile elastic modulus

In nature,there are widely distributed bi-modulus materials with different deformation characteristics under compressive and tensile stress states,such as concrete,rock and ceramics.Due to the lack of constitutive model that could reasonably consider the bi-modulus property of materials,and the lack of simple and reliable measurement methods for the tensile elastic parameters of materials,scientists and engineers always neglect the effect of the bi-modulus property of materials in engineering design and numerical simulation.To solve this problem,this study utilizes the uncoupled strain-driven constitutive model proposed by Latorre and Montáns(2020)to systematically study the distributions and magnitudes of stresses and strains of bi-modulus materials in the three-point bending test through the numerical method.Furthermore,a new method to synchronously measure the tensile and compressive elastic moduli of materials through the four-point bending test is proposed.The numerical results show that the bi-modulus property of materials has a significant effect on the stress,strain and displacement in the specimen utilized in the three-point and four-point bending tests.Meanwhile,the results from the numerical tests,in which the elastic constitutive model proposed by Latorre and Montáns(2020)is utilized,also indicate that the newly proposed measurement method has a good reliability.Although the new measurement method proposed in this study can synchronously and effectively measure the tensile and compressive elastic moduli,it cannot measure the tensile and compressive Poisson’s ratios.

Tensile Elastic Modulus, Strength and Fracture of δ-Al_2O_(3f)/Al Alloy Composites

Based on the experimental and theoretical analysis, the tensile elastic modulus, strength and fracture characteristics of squeeze casting δ-Al2O3/Al alloy composites were studied. The fracture characteristics of composites were observed by SEM. The elastic modulus was predicted by the finite element method based on the energy equivalence principle, and the strength was predicted by the statistical integration average method using the maximum energy criterion of composite strength. In the prediction, the distribution density functions of the fiber's. orientation and length were considered. These functions were gained by experimental measurement. It is shown that the predicted results are in agreement with the experimental values well and the microstructure feature of composites controls the fracture characteristics.

Study on the Tangential Tensile Mechanical Properties of Moso Bamboo

In this work,we used tensile tests to analyze the tangential failure forms of raw bamboo and determine a relationship between tangential tensile strength,elastic modulus,position,density,and moisture content.We found that the tangential mechanical properties of the culm wall were mainly dependent on the mechanical properties of the basic structure of the thin wall.Formulas for calculating the tangential tensile strength of moso bamboo and adjusting the moisture content were also determined.The tangential tensile strength and the tangential tensile modulus of elasticity(TTMOE)followed:outer>middle>inner,and diaphragm>bamboo node>culm wall.Below the fiber saturation point,the tangential tensile strength and TTMOE values of the bamboo gradually decreased with increasing moisture content.When the moisture content was 15%,the tangential tensile strengths of the inner,middle,outer,culm wall,bamboo node,and diaphragm samples of the five-year-old moso bamboo were 3.17,3.29,3.31,3.24,3.67,and 8.85 MPa,respectively.Furthermore,their TTMOE values were 215.09,227.98,238.45,224.04,267.21,and 559.27 MPa,respectively.Hence,this study provides a theoretical basis for future research on bamboo cracking.

Effect of Aramid/Carbon Hybrid on the Tensile Properties of Multilayered Biaxial Weft Knitted Fabric Reinforced Composites

The effects of aramid/carbon on tensile properties of multilayered biaxial weft knitted( MBWK) fabric reinforced composites are analyzed by experiments. The tensile tests are inducted by the SHIMADZU AG-250 KNE universal material testing machine and Aramis V6 digital image correlation( DIC) technique.More specifically,the composite samples own four hybrid ratios(Na∶ Nc= 12∶ 0,8 ∶ 4,6 ∶ 6 and 4 ∶ 8). The results showed that the aramid/carbon hybrid MBWK fabric reinforced composites showed nearly linear response until reaching the maximum load and the inserting yarns distribution on the surface of MBWK fabrics reinforced composites had a great influence on the strain pattern distribution. Besides,the tensile strength,the tensile modulus and the elongation at breakage of 0° samples and 90° samples increased with the decreasing of aramid/carbon hybrid ratio. In a word,the changes of tensile strength, tensile modulus and elongation at breakage have a lot to do with the difference of aramid/carbon hybrid ratio.

Size and strain rate effects in tensile strength of penta-twinned Ag nanowires

Penta-twinned Ag nanowires（pt-AgNWs） have recently attracted much attention due to their interesting mechanical and physical properties. Here we perform largescale atomistic simulations to investigate the influence of sample size and strain rate on the tensile strength of pt-AgNWs. The simulation results show an apparent size effect in that the nanowire strength（defined as the critical stress for dislocation nucleation） increases with decreasing wire diameter. To account for such size effect, a theoretical model involving the interaction between an emerging dislocation and the twin boundary has been developed for the surface nucleation of dislocations. It is shown that the model predictions are in quantitative agreement with the results from atomistic simulations and previous experimental studies in the literatures. The simulations also reveal that nanowire strength is strain-rate dependent, which predicts an activation volume for dislocation nucleation in the range of 1–10b^3,where b is the magnitude of the Burgers vector for a full dislocation.

CRYSTALLIZATION AND MECHANICAL PROPERTIES OF BLENDS OF METALLOCENE SHORT CHAIN BRANCHED POLYETHYLENE WITH CONVENTIONAL POLYOLEFINS

Metallocene-catalyzed short chain branched polyethylene (SCBPE) was blended with LDPE, HDPE, PS, EPDM and iPP in the weight proportions of 80 and 20. The crystallization and mechanical properties of these blends were studied by PLM, DSC and DMA. It has been observed in PLM that SCBPE/LDPE, SCBPE/HDPE and SCBPE/EPDM can form band spherulites whose band width and size are both smaller than that of the pure SCBPE. Tiny crystallites are observed in the completely immiscible SCBPE/PS blend. The crystallites in SCBPE/iPP are very small and only irregular spherulites are seen. The crystallization kinetics and mechanical properties of SCBPE are greatly affected by the second polyolefin, but in a different way, depending on the phase behavior and the modulus of the second components. SCBPE may be phase miscible in the melt with HDPE, LDPE and EPDM and co-crystallize together with HDPE or LDPE during cooling. A big change of crystal morphology and crystallization kinetics is seen in SCBPE/iPP blend compared with pure SCBPE and the lowest tandelta is also seen for this system. DMA results show that the tensile modulus of the blends has nothing to do with phase behavior, but only depends on the modulus of the second component.

Mechanical Properties of Polyimide/Multi-walled Carbon Nanotube Composite Fibers

A series of polyimide（PI）/multi-walled carbon nanotube（MWCNT） composite fibers were prepared by copolymerizing a mixture of monomers and carboxylic-functionalized MWCNTs, followed by dry-jet wet spinning, thermal imidization, and hot-drawing process. The content of the carboxylic groups of MWCNTs significantly increased when treated with mixed acid, whereas their length decreased with treatment time. Both the carboxylic content and length of MWCNTs influenced the mechanical properties of the composite fibers. Fiber added with 0.1 wt% MWCNTs treated for 4 h exhibited the best mechanical properties, i.e., 1.4 GPa tensile strength and 14.30% elongation at break, which were 51% and 32% higher than those of pure PI fibers, respectively. These results indicated that a suitable MWCNT content strengthened and toughened the resultant PI composite fibers, simultaneously. Moreover, raising draw ratio resulted in the increase of tensile strength and tensile modulus of the composite fibers.

Mechanical properties of U-0.95 mass fraction of Ti alloy quenching and aging treatment:a first principles study

First principles plane wave pseudopotential method was executed to calculate the mechanical properties with respect to the uranium-0.95 mass fraction of titanium （U-0.95 mass fraction of Ti） alloy for quenching and aging, including the elastic modulus, the value of shear modulus to bulk modulus （G/B） and the ideal tensile strength. The further research has also been done about the crack mechanism through Griffith rupture energy. These results show that the elastic moduli are 195.1 GPa for quenching orthorhombic ~ phase and 201.8 GPa for aging formed Guinier-Preston （G.P） zones, while G/B values are 0.67 and 0.56, respectively. With the phase change of uranium-titanium （U-Ti） alloy via the quenching treatment, the ideal tensile strength is diverse and distinct with dif- ferent crystal orientations of the anisotropic ~ phase. Comparison of quenching and short time aging treatment, both of the strength and toughness trend to improve slightly. Further analysis about electronic density of states （DOS） in the electronic scale indicates that the strength increases continuously while toughness decreases with the aging proceeding. The equilibrium structure appears in overaging process, as a result of decomposition of metastable quenching 7 phase. Thereby the strength and toughness trend to decrease slightly. Finally, the ideal fracture energies of G.P zones and overaging structure are obtained within the framework of Griffith fracture theory, which are 4.67 J/m2 and 3.83 J/m2, respectively. These results theoretically demonstrate strengthening effect of quenching and aging heat treatment on U-Ti alloy.

Tough and Multi-responsive Hydrogels Based on Core-Shell Structured Macro-crosslinkers

Novel hydrogels based on core-shell structured macro-crosslinkers were synthesized, which exhibited high toughness and multiple responsiveness. Sodium dodecyl sulfate（SDS） micelles mediated by Na Cl were used to encapsulate hydrophobic stearyl methacrylate（C18） in the core, and hydrophilic 2-acrylamido-2-methyl-1-propanesulfonic（AMPS） monomers in the corona. Such core-shell micelles were simultaneously copolymerized with acrylamide monomers through free radical polymerization. As a result, hydrogels crosslinked by amphiphilic “poly（C18）-PAMPS” macro-crosslinkers were obtained. These hydrogels showed excellent tensile and compression strength and toughness. Cyclic compression loadingunloading tests demonstrated that the hydrogels were of outstanding fatigue resistance, and showed partial damage of energy dissipation mechanism. The damaged energy dissipation mechanism could be recovered at room temperature and the recovery could be accelerated at elevated temperatures. The hydrogels were sensitive to the change in p H and ion strength, showing reversible swelling/deswelling behaviors.

Reinforcement of Hydroxypropylcellulose Films by Cellulose Nanocrystals in the Presence of Surfactants

Hydroxypropylcellulose（HPC） films were prepared by casting with cellulose nanocrystals in the presence of anionic surfactant sodium dodecylsulphate（SDS） and cationic surfactant hexadecyltrimethyl ammonium bromide（CTAB）. The cellulose nanocrystals were isolated from maize straw, a biomass source produced in huge quantities as an agrowaste in Brazil. These bionanocomposite films had good transparency and their surface hydrophilic character was evidenced by static contact angle measurements. Thermogravimetry（TGA） measurement revealed that nanocrystals and surfactants changed the thermal stability of the HPC films. Dynamic mechanical analysis（DMA） showed that the tensile storage and loss moduli of the HPC films increased by increasing the contents of cellulose nanocrystals and surfactants, especially in the case of CTAB. This good reinforcing effect of HPC matrix can be explained as due to electrostatic attractive interactions brought about by the presence of CTAB and the nanocrystals.