Applied Mechanics and Materials Vols. 226-228

Abstract: The effect of polyamide 6 (PA6) microfiber and porous polyurethane (PU) on tensile strength and softness of the PA6 microfiber reinforced porous PU composites was investigated. The tensile strength to break the composites is close to that of the corresponding PA6 microfiber nonwovens. It indicates that the PA6 microfiber provides the tensile strength for the composites. The porous PU has little effect on the tensile strength of the composites. The softness of the composites is dependent on PU modulus, which decreases with increasing the PU modulus. In this work, optical microscope and scanning electron microscope (SEM) were used to study the morphology of the composites. The micrographs showed that the diameters of the PA6 microfibers and bubble holes are relatively uniform which are in the range of about 1 to 3 μm.

Abstract: Polypropylene reinforced by hemp fibers composites were prepared by injection method. An aging chamber was used to simulate and accelerate the natural ageing process. The influence of moisture and UV aging on the mechanical properties of the composites is studied in this paper. A modified law of mixtures applying to polypropylene/hemp fibers composites is proposed. The microstructures of the composites during aging treatment were analyzed by means of digital microscope. We can see that the moisture and UV aging reduced the mechanical properties of the composites. The UV aging is more penalizing on the mechanical properties of composites, compared to the moisture aging after 4 weeks of exposure.

Abstract: Based on the least squares theory and a damage variable , a damage model is formed for the freeze-thaw degradation of the layered hybrid fiber reinforced concrete (LHFRC). By the model the degradation equations for the LHFRC and the plain concrete(PC) are regressed with the experimental data, which are identical in the initial phase and different in the damage propagation phase and the is used to describe the damage process of concrete subjected to freeze-thaw cycles. The of LHFRC is smaller than that of PC in the damage propagation phase. Furthermore, the frost resistance of LHFRC is stronger than that of PC due to steel fibers and polypropylene fibers having retarded the degradation of concrete.

Abstract: In this work, the adsorption of naphthalene-based water reducer (FDN) on slag ground with or without the composite retarder YP-3 and PN (YP) in alkali-activated slag cement (AASC) activated by water glass (WG) has been studied in detail. The results show that the effect of the adsorption of water reducer on AASC depends directly on the dosage of the water reducer and on the composite retarder used. For example, mixed slag particles adsorb thrice as much water reducer FDN than pure slag particles at 1% mass of the slag, and the absolute value increment of the zeta potential of the AASC suspension containing the composite retarder is 8.61 mV, compared with 1.99 mV in the system without the composite retarder. Moreover, the AASC pastes activated by WG containing the retarder YP show better rheological properties and lower fluidity loss over time.

Abstract: To study the problem of the relation between the performance of cement base composite material and the dosage of the iron ore. Because of the gradually reducing of natural sand, people will pay attention to the use of the iron ore. The study shows the effect of the iron ore dosage of cement base composite material on the performance based on this condition. We mix with different dosage of iron ore in the test. Try to do the flexural strength test and the flexural strength is the highest of all when the dosage of iron ore is 60%. At the same time try to analyse the energy and we find the energy needed in the process of fracture is highest when the dosage of iron ore is 60%. So we can choose the 60% the iron ore used in practical application instead of the natural sand.

Abstract: An improved passive confining pressure SHPB method was used to study the dynamic mechanical behaviors of asphalt concrete under quasi-one dimensional strain state. The effect of confining jacket material and its geometrical sizes on the confining pressure were discussed. The dynamic strength, dynamic modulus of elasticity and dynamic Poisson ratio of asphalt concrete were obtained. The influential rules of confining pressure on the dynamic properties were studied by comparing the stress-strain curves of asphalt concrete under different stress states. The study found that passive confining greater impact on the strength of asphalt concrete than elastic modulus and Poisson ratio, but the elastic modulus improved with the increase of confining pressure.

Abstract: Ultrasonic testing technique is an important nondestructive testing method, which has been widely used to the defect detection of CFST and is the preferred alternative for concrete close-grained degree and uniformity test. The test becomes difficult when the diameter of the concrete-filled steel tubular is less than 250mm,as the combination of different media and the reduction of dimension on CFST increase the difficulty degree of detection. As the experimental research basis, 4 different preinstalled-defect CFST are produced. The principle and methodology of Ultrasonic detection is comprehensive researched on the signal characteristics, such as wave speed, wave amplitude, sound speed and wave shape, etc. It gives useful suggestions for the theory and practice of identification of defect types and the quality control in small diameter CFST.

Abstract: In this paper, it makes a preliminary study on the material of carbon fiber sheet to reinforce rough sleeper beam in order to enhance the magnitude of ultimate flexural bearing capacity. Considering the actual construction technology and environment, four reinforced concrete sleeper beams are used to experiment simulation to study the influence of carbon fiber sheet to ultimate flexural bearing capacity of reinforced concrete structures. Experiment results show that pasting two layers of carbon fiber sheet under reinforced concrete beam can have about a 25% increase in flexural bearing capacity.

Abstract: A new criterion (failure stress criterion) is presented for the mixed-mode fracture of concrete by comprehensively evaluating several mixed-mode crack criteria. The new criterion absorbs some results fitting in with concrete from G.C.Sih and Erdogen’s maximum circumference stress criterion and G.C.Sih’s minimum strain energy intensity factor criterion. It combines concrete material fracture property with the condition of loads at the moment of concrete fracture by Weibull theory. It is concluded that concrete crack expands neither along the direction of maximum circumference stress nor along minimum strain energy factor S. The crack extends along the direction limited in the area controlled by two criteria. The accurate crack position is determined by failure probability of the strength of concrete structure. The experimental results indicate that the new criterion has better precision and adaptability comparing with other criteria and it can be applied to engineering very well.

Abstract: Different content of foaming agent in the lightweight aggregate concrete test, the apparent density and compressive strength of concrete assessment indicators. Studies have shown that, with the dosage increase, the variation of the apparent density of the concrete is first decreases and then increases when the content is 0.8kg/m3 dry apparent density minimum; as the foaming agent content continues to grow, dry apparent density continues to increase, but the magnitude of increase is less obvious. At this point, its 28 days compressive strength of only 0.7MPa, the wall strength of the material does not meet the insulation requirements. Taking into account the apparent density and strength of wall insulation materials, requirements, test data to determine the optimal dosage of the foaming agent should be 0.4 ~ 0.6kg, to determine the content of foaming agent in the lightweight aggregate concrete of the most good range.