Studying the Failure Behavior of Cement-fiber-treated Sand under Triaxial Direct Tension Tests

The main goal of this research is to study the failure behavior of cement-fiber-treated sand under triaxial direct tension condition tests. Thus, a new loading system and triaxial cell was designed and built for tensile loading. Samples were prepared with content cement of 3 and 5% (dry wt.) of the sand, while two types of polypropylene fibers 0.024 m in length and 23 μm and 300 μm thick were added at 0.0% and 0.5% (dry wt.) of the sand and cement mixture. After a seven-day curing period, the samples were loaded under triaxial direct tension tests under confining pressures of 100, 200, and 300 kpa in drained conditions. Stress-strain behavior, changes in volume and energy absorbed by cement-fiber reinforced sand were measured and compared with the results of other studies. Adding fibers resulted in reduced peak deviatoric stress and increased residual deviatoric stresses of the cement-fiber reinforced sand, with changes from brittle to ductile behavior. The initial stiffness and stiffness at 50% maximum tensile stress of the samples is decreased with the addition of fibers and with an increase in fiber diameter, the reduction rate of this stiffness is more evident. The absorbed energy for fibers with a thickness of 23 μm is less than fibers with a thickness of 300 μm. The effect of adding fibers to strength parameters showed that the cohesion intercept decreases, while the internal friction angle increases.

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.

A Most-Unfavorable-Condition Method for Bridge-Damage Detection and Analysis Using PSP-InSAR

The main contribution of this study is to provide a new idea to detect bridge damage by using PSP-InSAR technology. A most-unfavorable-condition method is proposed for bridge-damage detection and analysis. The method can determine the specific damaged location and occurrence time by using the differential deformation values of persistent scatterer (PS) points on bridge piers. Taking Beijing Suzhou Bridge as an experimental area, 96 COSMO-SkyMed time-series SAR images were used from September 2011 to November 2017. Deformation values of PS points around Suzhou Bridge were acquired and analyzed. Experimental results show that in July 2017, the unusual maximum differential deformation value was 25.73 mm. It occurred between piers D3 and D4 of Suzhou Bridge, and it was deduced that the main girder between piers D3 and D4 may have been damaged in July 2017. As a validation, taking the differential deformation value between piers D3 and D4 as an input, the maximum tensile stress, and the maximum compressive stress were calculated as 2.1 MPa and 8.4 MPa, respectively, through a finite element model. The tensile stress exceeded the design value of the concrete, further confirming the damage of the girder between piers D3 and D4. Moreover, all results are consistent with the Suzhou Bridge damage information shown in existing records, which verify the accuracy and reliability of the proposed method.

Flexible crosslinking of polyurethane using grafted poly(dimethylsiloxane) with Epichlorohydrin and Bisphenol A end groups and its impact on the mechanical properties and low-temperature flexibility

Poly(dimethylsiloxane) (PDMS) was grafted onto polyurethane (PU), and Epichlorohydrin and Bisphenol A were attached to the free ends of PDMS groups and used to link the grafted PDMS to thereby introduce flexible crosslinks between the PU chains. The flexible crosslinks enhanced the crosslink density and solution viscosity of PU but did not change the melting and crystallization behaviors of the soft segments of PU. In particular, the flexible PDMS crosslinks increased the maximum tensile stress by up to 300% and the maximum tensile strain up to 180%. The shape recovery capability at 10°C and the shape retention capability at −25°C were maintained above 90% with the flexible crosslinking. Grafted PDMS moderately improved the low-temperature flexibility of PU due to its flexibility at low temperature. The flexible crosslinks of grafted PDMS successfully improved the tensile strength, shape recovery, and low-temperature flexibility of the PU.

Additional forces on continuously welded rails of a long-span high-speed railway suspension bridge under single effect and multiple effects: A case study

This paper investigates the track–bridge interactions of the Wufengshan Yangtze Bridge, the longest high-speed railway suspension bridge in China. A finite element model of the track and bridge is built using the commercial software ANSYS. The longitudinal additional forces of the track under a single effect and combination effects of temperature rising load, bending load, and braking load are calculated. The numerical results show that strong additional forces appear in the continuously welded rail of the Wufengshan Yangtze Bridge. Temperature effect is the dominant factor for the residual internal forces. The maximum tensile stress is 115.5 MPa and the extreme compressive stress reaches 329.9 MPa. Rail expansion joints are needed for this long-span suspension bridge.

Measuring and Testing Composite Materials Used in Aircraft Construction

This paper is focused on the use of special composite materials for the construction of aircraft components. It focuses on measuring and testing the strength of reinforced composite materials used in damaged aircraft parts repairs. To determine the layer required to repair a part of the aircraft, it is necessary to know the strength limit of the material and its parts. The article describes experimental measurements of manufactured composite samples that have been subjected to tensile stress. Aim of the performed tensile tests was to determine the maximum tensile stress that the composite materials are able to transmit until they are damaged. Measurement determining the maximum stress level is important to ensure the required safety of the aircraft structure on which the composite structure was repaired.

Effect of T-stress on Fracture of a Long Cracked Plate in Unsteady Heat Transfer

In order to accurately predict the structure fracture caused by thermal load, a modified maximum tensile stress (MTS) criterion combined with T-stress is proposed. The modified MTS uses a two-parameter model (stress intensity factor K and T-stress) to describe the fracture behavior under thermal load. The T-stress and stress intensity factor at the crack tip are solved by using J-integral in the theoretical calculation of a cracked strip with temperature difference. The results show that T-stress can affect the fracture toughness and the stress at the crack tip of the cracked strip with temperature difference. This provides a basis for the simulation of structural fracture under thermal load.

Study On The Effect of Tunicate Cellulose Nanocrystals in The Preparation of Sodium Alginate-Based Enteric Capsule

In this work, the tunicate cellulose nanocrystal (tCNC) was extracted from tunicate by bleaching and acid hydrolysis. It was used as filler in the preparation of sodium alginate-based enteric capsule. The addition of tCNC with high aspect ratio (65) rendered the enteric capsule excellent physical properties. Compared with the control sample, when the addition of tCNC was 10% (wt), the water contact angle of the capsule was enhanced by 46.0%, the opacity was increased by 356.8%, the maximum tensile stress was increased by 142.6%, the modulus of elasticity was increased by 240.3%, and the elongation at break was increased by 133.8%. In the in vitro degradation experiments, the capsule hardly degraded in the gastric environment (pH 1.2), while in the intestinal environment (pH 6.8), the degradation became slower with the increase of tCNC content, which was consistent with the properties of enteric capsule. This research developed a new direction for the application of tCNC in the pharmaceutical material productions.

Mixed Mode Crack Propagation in Iliac Bone

Bone is a complex material that can be regarded as an anisotropic elastic composite material. The problem of crack propagation in human bone is analyzed by using a generalization of the maximum tensile stress criterion (MTS). The results concern the critical stress for crack propagation and the direction of the crack path in Iliac bone.

High-Performanced Hemicellulose Based Organic-Inorganic Films with Polyethyleneimine

For the high-value utilization of hemicellulose-based composite films, the poor film-forming and mechanical properties of hemicellulose-based composite films must be surmounted crucially. Based on this, hemicellulose-based organic-inorganic composite films with good mechanical properties were prepared from quaternized hemicelluloses (QH), bentonite, and polyethyleneimine (PEI). The QH/PEI/bentonite composite films were prepared by vacuum filtration, and the properties of the composite film were investigated. The results showed that the QH was inserted into bentonite nanosheets through hydrogen bonding and electrostatic interactions. PEI was cross-linked with hemicellulose by hydroxyl groups, electrostatically attracted by the bentonite flake layers. The mechanical properties of the composite films were significantly increased by the incorporation of PEI. When the PEI content was 20%, the tensile stress of the composite film was increased by 155.18%, and the maximum tensile stress was reached 80.52 MPa. The composite films had strong UV absorption ability with the transmittance was almost 0 in the UV region from 200 to 300 nm. The thermal property of composite film was also improved, and the residual mass increased by three times compared to QH. These results provide a theoretical basis for the use of hemicellulose-based composite films in packaging applications.