Influence of Nanoscale Inhomogeneity Incorporating Interface Effect on Crack Nucleation at Intersection of Twin and Grain Boundary in Nanocomposite

Nanocracks can generate at the intersection of the deformation twin and grain boundary (GB). A mathematical model is built to study the nanoinhomogeneity effect on nanocrack nucleation and propagation in the nanocrystalline matrix. The boundary condition at the interface between the nanoinhomogeneity and the matrix is modified by incorporating the interface effect. The influence of the nanoinhomogeneity shear modulus, the nanoinhomogeneity radius, the nanoinhomogeneity position, the interface effect, and the external stress on the nanocrack nucleation and propagation is investigated in detail. The results indicate that the stiff nanoinhomogeneity suppresses nanocrack nucleation and propagation and thereby improves the tensile ductility of nanocomposites without loss of their predominantly high strength. Both the positive interface residual tension and interface elastic constants suppress nanocrack nucleation and propagation, while the negative interface residual tension and interface elastic constants promote nanocrack nucleation and propagation. Furthermore, the effect of interface residual tension is rather significant. The interface elastic constants have a weak effect on nanocrack nucleation and propagation.

The Effect of Composite Cement (ECC) as A High Performance Fiber Reinforced Composite Cement

Composite Cement (ECC) addresses a special type of high performance fiber reinforced composite cement with high tensile ductility. Fibers have been used to increase the toughness of quasi-brittle cement-based materials. As a result of its ability to produce high tensile ductility, ECC originally designed its strain-hardening behavior using a micromechanical concept, so that over-tensile strain capacity could be achieved in excess of 2% through multiple cracks. This research method is carried out by means of laboratory testing in accordance with data from literature studies both Indonesian SK SNI Standards and foreign standards, namely ASTM. The method applied in this research is an experimental method. The independent variable in this study is the reinforcement with the addition of fiber to the PVA ECC material mix, while the dependent variable in this study is the compressive strength value and the magnitude of the elastic modulus of the PVA ECC material. The results of the tensile strength of the ECC PVA material obtained on average at the age of 7, 14 and 28 days were 3.108 MPa, 3.547 MPa and 4.34 MPa, respectively. The tensile strength of the ECC PVA material increases with age. The average modulus of elasticity of PVA ECC material obtained at the age of 7, 14 and 28 days was 18763.02 MPa, 20788.81 MPa and 21060.03 MPa, respectively. Based on the modulus of elasticity, it also increases with the increase in compressive strength.

Deformation Twinning Induced High Tensile Ductility of a Gradient Nanograined Cu-Based Alloy

We investigated the tensile properties of gradient nanograined Cu and CuAl samples prepared by plastic deformation. Tensile tests showed that the gradient nanograined Cu-4.5Al sample exhibits a uniform elongation of ~22% without any cracks, while the uniform elongation of the gradient nanograined Cu sample is only ~18%. Numerous mechanical twinning retards the softening of the nanograins and accommodates a high tensile ductility in the gradient nanograined Cu-4.5Al sample. This work indicates that mechanical twinning is a potential deformation mechanism to achieve high tensile ductility of nanograined materials.

Effect of Raw Sugarcane Bagasse Ash as Sand Replacement on the Fiber-Bridging Properties of Engineered Cementitious Composites

The use of raw sugarcane bagasse ash (SCBA) as sand replacement in the production of engineered cementitious composites (ECCs) can improve its cost-effectiveness and practicality. A recent study by the authors showed that the use of raw SCBA as a replacement to sand in ECC mixtures substantially enhances the tensile ductility and provides mild improvements in tensile strength; however, it also indicated a need to further elucidate the mechanisms producing such improvements. Therefore, the present study examined the effects of raw SCBA as a sand replacement in ECC’s fundamental fiber-bridging relationship, [Formula: see text], through single crack tensile test (SCTT) using 1% polyvinyl alcohol (PVA) fiber volume fraction. The PVA fiber volume fraction was reduced from 1.5% in the previous study to 1% in this study to ensure that a single crack was produced, which is a necessary condition to obtain the fundamental [Formula: see text] relationship. A total of five mixtures were evaluated at different replacement levels of sand with raw SCBA (i.e., 0%, 25%, 50%, 75%, and 100%). SCTT results revealed that raw SCBA produced minor effects on the fiber-bridging capacity but significantly increased the complementary energy ( [Formula: see text]). A positive correlation was observed between the pseudo strain-hardening (PSH) strength index and raw SCBA content. Since the PSH strength index was higher than the recommended value (i.e., 1.3) for robust PSH behavior, it was concluded that the main factor contributing to tensile ductility enhancements was the increase in the PSH energy index resulting from the notable increase of [Formula: see text] and potential decrease in matrix fracture toughness.