Key Engineering Materials Vols. 385-387

Abstract: Scattering of SH wave by an elastic half space with a lining structure and a crack in any position and direction is studied with Green’s function, complex function and multi-polar coordinate method. First, a suitable Green’s function is constructed, which is a fundamental solution to the displacement field for the elastic space possessing circular lining structure while bearing out-of-plane harmonic line source load at arbitrary point. Then a crack in any position and direction is constructed by means of crack-division in half space. Finally the displacement field and stress field are established in the case of coexistence of circular lining structure and crack, and the expression of dynamic stress intensity factor (DSIF) at the tip of crack is given. According to numerical examples, the influences of different parameters on DSIF are discussed.

Abstract: In this paper, 3D continuum damage mechanics (CDM) incorporated with layer-wise theory and interface element is employed to investigate the progressive damage inside and between the laminate's layers under quasi-static axial loading. For this purpose, a finite element program is developed. To simulate the delamination, a quadratic interface element is used which is compatible with the 8-node numerical layers of layer-wise theory. Matrix cracking and delamination initiation and propagation of [302/-302]s angle-ply laminate are investigated and the obtained results are compared with the available experimental evidence.

Abstract: The purpose of this study is to establish a simple approach to compute the chloride diffusivity of (non)carbonated concrete. The chloride diffusivity of concrete should is defined, based on engineering and scientific knowledge of cement and concrete materials. In this paper, parameters affecting the chloride diffusivity, such as the diffusivity in pore solution, tortuosity, micro-structural properties of hardened cement paste, volumetric portion of aggregate, are taken into consideration in the calculation of the chloride diffusivity of noncarbonated concrete. For carbonated concrete, reduced porosity due to carbonation is calculated and used for calculating the chloride diffusivity. The results are compared with experimental data and previous research works.

Abstract: Statistical analysis is presented for 108 groups of fatigue test data of concrete, including tests of abnormal value, variance and distribution-fitted with fuzzy optimization; analysis of variance, sample size and error. It is chiefly concluded that effect of stress level of repeated loading on the fatigue life of concrete is much more significant than that of stress rate and relative stress amplitude, and effect of stress rate and relative stress amplitude are of the same significance; Relationship of sample size, relative error and significant level is also presented; fatigue life of concrete is more fitted for lognormal distribution than Weibull distribution. Suggestion for relevant code, standard and regulation are presented.

Abstract: The amount of waste glass sent to landfill has increased over recent years due to an ever growing use of glass products. Landfilling can cause major environmental problems because the glass is not biodegradable material. However, waste glass can be used as fine aggregate, coarse aggregate and powder form in concrete. The fine and coarse aggregate can cause alkali-silica reaction (ASR) in concrete, but the powder form can suppress their ASR tendency and acts as a pozzolanic material. This paper studies the expansion properties in concrete containing waste glass, silica fume, rice husk ash and polypropylene fibers in detail.

Abstract: Based on compliance testing of a straight-notch compact tensile (SN-CT) or a single edge bending (SEB) specimen, this paper present a formula with increment form to calculate plastic part of J-integral, two formulas for a SN-CT specimen and a SEB specimen to transform crack mouth opening displacement (CMOD) v0 to the crack opening displacement (COD) q along load line, and simplified formulas to estimate crack length a and effective young’s modulus E. Furthermore, the relation between v and q of the SN-CT specimens of 45 steel and SEB specimens of 30Cr steel were investigated. The results show that the formulas to describe the relation between the ratio v/q and the dimensionless crack length a/w of the specimens accord with the testing results better.

Abstract: The fracture resistance of asphalt materials significantly influences the service life of asphalt pavements and consequently affects the maintenance and rehabilitation costs of the pavement network. Therefore, there is significant interest in understanding the mechanism of fracture in asphalt pavements and in developing analysis tools that would lead to the selection of asphalt materials with increased fracture resistance. Study of cracking behavior of asphalt mixtures should be conducted in a micro-scale level to have a real simulation of crack propagation. Using SIEMENS SOMATOM plus X-ray CT (computerized tomography) and multi-functional testing rig, a dynamic observation of cracking propagation of hot mix asphalt was conducted in this research. Failure process under compressive pressure was recorded using CT images and CT numbers. The direct responses in density change of Marshall Samples under a CT-compressive process are change of CT numbers. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. The tests reported provide important theoretical fundamentals to study the cracking behavior and failure mechanism of asphalt mixtures.

Abstract: Cracking has long been accepted as a major mode of premature failure in flexible pavements. Expected life of pavements, pavement condition and maintenance cost are directly related to pavement cracking. It is crucial to have a sufficient understanding of cracking mechanism in order to produce a sound and safe material and structural design of asphalt pavements. Simulation, surveying, observation, and measurement of cracking in pavement structures have been reported in literature in last three decades. However, cracking process in asphalt mixtures in a three dimensional scale is still a great challenge to road engineers. Using SIEMENS SOMATOM plus X-ray CT (computerized tomography) and multi-functional testing rig, a dynamic observation of cracking propagation of hot mix asphalt was conducted in this research. Marshall samples of AC20 were used under uniaxial compressive stress state. Stress and strain behavior was observed during the compressive failure process of asphalt mixtures. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. Research results show that loading rate is a critical factor influencing cracking velocity and cracking density.

Abstract: A new sort of high performance concrete is introduced which combines most advantages of prestressed concrete and steel fiber concrete, named steel fiber reinforced self-stressing concrete(SFFRSSC for short). Self-stressing concrete is actually a kind of expansive concrete which self-stresses, namely pre-compressive stresses, are induced by dint of some restrictions generally provided by steel bars to concrete expansion after hydration of expansive cement. As a result of chemical reaction, concrete archived prestresses by itself different from mechanical prestressed concrete, so called self-stressing concrete. By distributing short-cut steel fibers into self-stressing concrete at random, prestresses( self-stress) are created in concrete under combined restriction of steel bars and steel fibers. Thank to the pre-stresses tensile strength of concrete are significantly increased as well as cracking strength. In addition, expansive deformation of SFFRSSC can compensate the shrinkage of concrete to decrease shrinkage crack, and the steel fibers play an important role in post-crack behavior. On the other hand, self-stressing concrete can avoid the troubles of construction compared with conventional mechanical prestressed concrete. For purpose of understanding the properties of SFFRSSC, in this paper some researches were carried out to investigate the special expansive behaviors of restrained expansive deformation with restriction of steel bar as well as steel fiber. The test results indicated that steel bar and steel fiber both provide effective restrict to self-stressing concrete as result of forming prestresses in concrete.

Abstract: In this paper, the dynamical behaviors of the centrifugal flywheel governor with external disturbance are discussed, and the system exhibits exceedingly complicated dynamic behaviors. The influence of system parameter on the chaotic system is discussed through Lyapunov-exponents spectrum and global bifurcation diagram, which accurately portray the partial dynamic behavior of the system. It is chaotic with proper system parameter, and we utilize Poincaré sections to study the Hopf bifurcation and chaos forming of the centrifugal flywheel governor system. Then, we utilize coupled-feedback control and adaptive control to realize the chaotic synchronization and obtain the conditions of chaos synchronization. Finally, we carry on the theory proof using the Lyapunov stability theory to the obtained conditions, the theoretical proof and number simulation shows the effectiveness of these methods.