Effect of freeze and thaw cycle on the mechanical properties of engineered cementitious composites with un-oiled fibers containing liquid and solid polymers

Nowadays, the application of the engineered cementitious composites(ECC) is expected to highly develop. Due to the lack of access to oiled- polyvinyl alcohol (PVA) fibers in many parts of the world, the implementation of the ECC has contained many difficulties. In this study, to increase the mechanical properties of ECC with the use of un-oiled PVA fibers, the polymers of styrene butadiene rubber (SBR), and ethylene vinyl acetate (EVA) were taken into account to resolve the abovementioned issue. Herein, also in order to enhance the tensile and flexural properties of ECC, the cement was replaced by polymers. Accordingly, a total of 7 mix designs were planned to conduct the proposed tests. The compressive strength, uniaxial tensile strength, and three-point bending tests were performed on the ECC at their 28-day age with consideration of the freeze and thaw cycle. The results of this research illustrated that the use of polymers can enhance the tensile and flexural properties of the ECC with un-oiled PVA fibers. The tensile strain in this study increased by more than 3% after the application of the polymers. Furthermore, the compressive strength increased by more than 47 MPa, and the deflection at the mid-span reached more than 9 mm in the bending test. However, the results showed that the use of polymers was effective on the freeze and thaw cycle and almost preserved the mechanical properties of the ECC. SBR latex has higher compatibility with the ECC in comparison with EVA powder.

Experimental Investigation on the Mechanical Properties of Polypropylene Hybrid Fiber-Reinforced Roller-Compacted Concrete Pavements

To explore the effect of multi-scale polypropylene fiber (PPF) hybridization on the mechanical properties of roller-compacted concrete (RCC), the early-age (3, 7, 14, 28 days) compressive strength, splitting tensile strength and uniaxial tensile test of RCC reinforced with micro-, macro- and hybrid polypropylene fibers were investigated. Then, the tensile stress–strain curve of polypropylene fiber-reinforced roller-compacted concrete (PFRCC) and the corresponding tensile parameters were obtained. The uniaxial tensile constitutive equation of PFRCC and fiber hybrid effect function was also proposed. Finally, the enhancement mechanism of fiber hybridization on mechanical properties of RCC was analyzed. The results indicated that the strength and toughness of PFRCC improved with the incorporation of PPF, showing obvious plastic failure characteristics of PFRCC. Before curing the concrete for 7 days, micro-PPF played a major role in strengthening RCC, while macro-PPF played a major role in reinforcing concrete after that. Moreover, the tensile strength and toughness indexes of multi-scale PFRCC performed the best, indicating the positive hybridization of three types of PPF. The proposed PFRCC uniaxial tensile constitutive equation and fiber hybrid effect function based on existing researches were also well matched with the experimental results.

Experimental and numerical investigation of metal-polymer riveted joints

This paper presents the modeling and analysis of the joints of metal inserts with polyamide 6 using the injection technique. Based on the conducted experiments, modeling and numerical calculations of joints were carried out for various joint configurations. Metal parts, made of steel grade DC 04, are mechanically locked with polyamide 6 (PA6) with rivets. The mechanical connection with rivets of both elements was achieved by filling the holes in the metal parts in the injection process. As part of the work, mechanical-clamp connections made of steel / PA6 were mechanically tested in a single-axis joint tensile test using appropriate tabs. The main goal was to study and numerically analyze the number of rivets and their location on the metal plate for the strength of the connector. An important element of the work was the modeling process of both the PA6 material behavior and the joint itself. As part of the experimental research, the rivet deformation was also observed using computer thermography with the use of an IR camera. The tests and simulation showed that for the sample, the polymer-metal connected with less than three rivets was destroyed by shear. On the other hand, when the polymer-metal junction was made of three rivets, the jamming mechanism was mainly related to damage to the polymer part. For these joints, the maximum values of the breaking force of the joint were obtained in uniaxial tensile and shear tests where three rivets were used. Similar values were obtained during the numerical calculations performed with the use of Abaqus software.

Fabrication of Nanopore in MoS2-Graphene vdW Heterostructure by Ion Beam Irradiation and the Mechanical Performance

Nanopore structure presents great application potential especially in the area of biosensing. The two-dimensional (2D) vdW heterostructure nanopore shows unique features, while research around its fabrication is very limited. This paper proposes for the first time the use of ion beam irradiation for creating nanopore structure in 2D vdW graphene-MoS2 heterostructures. The formation process of the heterostructure nanopore is discussed first. Then, the influence of ion irradiation parameters (ion energy and ion dose) is illustrated, based on which the optimal irradiation parameters are derived. In particular, the effect of stacking order of the heterostructure 2D layers on the induced phenomena and optimal parameters are taken into consideration. Finally, uniaxial tensile tests are conducted by taking the effect of irradiation parameters, nanopore size and stacking order into account to demonstrate the mechanical performance of the heterostructure for use under a loading condition. The results would be meaningful for expanding the applications of heterostructure nanopore structure, and can arouse more research interest in this area.

Expanded (Black) Cork for the Development of an Eco-Friendly Surfboard: Environmental Impact and Mechanical Properties

Based on global needs for sustainable development, finding new sustainable materials that can replace oil-based ones for mass products is crucial nowadays. This paper focuses on employing an expanded cork-based composite to produce a surfboard. To evaluate the mechanical properties, uniaxial tensile and compression tests were performed on the skin and core materials, respectively. Bending tests were performed on the entire representative composite structure. Numerical models of the tests were arranged and validated from experimental results. From that, a surfboard prototype model was used to simulate some experimental conditions, permitting us to draw promising conclusions. An actual prototype was also produced. It was found that expanded cork performs very well when sandwiched between wood and polyester resin/glass fibre, being able to hold substantial loads and at the same time reduce weight and the environmental footprint of the composite by 62.8%. It can be concluded that expanded cork is an excellent candidate to replace oil-based foams in surfboard manufacturing. Despite a slight increase in weight, this sustainable material aligns with all the philosophies of surf practice worldwide.

An Analytical Model for the Uniaxial Tensile Modulus of Plain-Woven Fabric Composites and Its Application and Experimental Validation

With advantages in efficiency and convenience, analytical models using experimental inputs to predict the mechanical properties of plain-woven fabric (PWF) composites are reliable in guaranteeing the composites’ engineering applications. Considering the importance of the aspect above, a new analytical model for predicting the uniaxial tensile modulus of PWF is proposed in this article. The composite yarns are first simplified as the lenticular-shaped cross-sections undulate along arc-composed paths. Force analyses of the yarn segments are then carried out with the internal interactions simplified, and the analytical model is subsequently deduced from the principle of minimum potential energy and Castigliano’s second theorem. The PWF of T300/Cycom970 is chosen as the study object to which the proposed analytical model is applied. Microscopic observations and thermal ablation experiments are conducted on the specimens to obtain the necessary inputs. The uniaxial tensile modulus is calculated and tensile experiments on the laminates are performed to validate the analytical prediction. The small deviation between the experimental and analytical results indicates the feasibility of the proposed analytical model, which has good prospects in validating the effectiveness of the experimentally obtained modeling parameters and guaranteeing the accuracy of mesoscale modeling for the PWF.

Tensile Properties of 3D-printed Continuous-Fiber-Reinforced Plastics

Obtaining parts made of composite materials through 3D Printing Additive manufacturing have fully proved their usefulness due to a number of advantages such as: the possibility to directly create complex shapes without going through the classic process of transforming the semi-finished products into finished parts through technologies which consume resources and energy and are totally unfriendly to the environment. The main disadvantage of the parts made by 3D Printing technologies is that they are less resistant from a mechanical point of view. This was solved with the emergence of the 3D printers capable of printing composite parts consisting of a plastic matrix reinforced with continuous fibers. This research focuses on studying 4 types of composite materials from the point of view of their mechanical properties: Onyx - a rigid nylon in which micro carbon fibers are inserted and Onyx reinforced with carbon, fiber glass or kevlar. Standardized specimens were made for the uniaxial tensile test and the experimental program was designed evaluating: the Elastic modulus [GPa], the Maximum Tensile stress [MPa], the Tensile strain at maximum Tensile stress [mm/mm]. The principal strains were also determined, by means of the digital image technique made using the Aramis system from GOM. The experimental tests confirm that these new materials will be serious candidates to be used in the engineering applications in various fields.