Papers by Keyword: Loading Frequency

Abstract: For the sake of studying the influence of loading frequency on the hydroxyl-terminated polybutadiene (HTPB) coating’s dynamic mechanical properties during aging, the one month’s thermal accelerated aging test was carried out at 70°C. The dynamic mechanical properties of the aged HTPB coatings were tested through dynamic mechanical analysis (DMA) Q800 with the loading frequency range of 0~100Hz, the dynamic strain amplitude of 0.1% and the test temperature of 25°C. The change models of the dynamic modulus with the loading frequency were established. The results showed that with the extension of the aging time, the storage modulus and the loss modulus both rose, which were related with the change of the crosslinking network structure. The storage modulus increased exponentially with the loading frequency, and the correlation coefficients fitted by the exponential models were all greater than 0.96. The loss modulus changed in sections. When the loading frequency was less than 70 Hz, the loss modulus showed a cubic function growth relationship with the loading frequency, and the correlation coefficients were larger than 0.98; when the loading frequency was between 70 Hz and 100 Hz, the loss modulus showed a quadratic function relationship with the loading frequency that first decreased and then increased, and the correlation coefficients were all larger than 0.97.

Abstract: The flexural modulus of composite laminates subjected to cyclic loads of varying cycle periods are experimentally investigated in this work. GFRP composite laminate specimen of configuration 0/R/0/0/0, 0/R/30/60/0, 0/R/90/90/0 and 0/R/45/-45/0 are prepared by hand lay-up technique with a uniquely processed resin-rich intermediate layer for the testing. Specimens are exposed to constant amplitude cyclic loading of frequencies 4.6 Hz and 8.6 Hz. A cantilever configuration of specimen with cyclic tip loading is considered to simulate the conditions of a leaf of a laminated automobile leaf spring. The flexural response of the laminate is measured using three point bend test as per ASTM D 790 and damping by hysteresis loop. The observed reduction in flexural modulusand the increase in damping factor after loading are compared with virgin. Minimised flexural modulus deviations between the loading frequencies are favoured by the cushioning of resin rich intermediate layer in the lay-up.

Abstract: In 3-point bending fatigue experiments of sandwich plate with visoelastic core and steel faceplates, it is found that response loading of specimen is very sensitive to cycling frequency. From fatigue test, different loading response of sandwich beam obtained in various cycling frequencies. Based on viscoelastic theory, responses of deformation of sandwich plate in cyclic square load wave are calculated. And an explanation of influences of cycling frequency is elaborated.

Abstract: Based on the theory of viscoelasticity, the Dynamic Shear Rheology test is used as study method. Study subjects are AH70 asphalt, SBS modified asphalt and MAC modified asphalt. Study objective is to analyze the effects of both high temperature and loading frequency on asphalt binder in asphalt mixture. Results from studies have revealed that: At high temperature and low loading frequency, the elasticity of asphalt binder decreases or low possibility of strain recovery, rutting resistance parameter decreases or the risk of rutting increases; At high temperature and high loading frequency, the viscosity of asphalt binder decreases or the strain speed of asphalt binder increases; At low temperature and high loading frequency, the fatigue resistance parameter increases, in other words there exists high fatigue cracking potential.

Abstract: It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation of X60 pipeline steel was employed to experimentally simulate the influence of dents and the fatigue fracture surfaces of X60 pipeline steel after per-tension deformation under cyclic loading were investigated. The results indicate that the static state tensile mechanics is the dominant factor in the fracture mechanisms at high stress ratio. With the decrease of the stress ratio R, the fractograph presents evident fatigue facture characteristics. The amount and intensity of MnS inclusion evidently increase with the loading frequency decrease and the typical cleavage fracture characteristics have been found.

Abstract: To study the mechanical properties of high modulus asphalt mixtures, dynamic modulus and phase angle of these two mixtures are tested with Simple Performance Testing System under different temperatures, loading frequencies and confining pressures. Testing results show the superiority of high modulus asphalt mixture in aspect of high temperature performance. Furthermore, the changing rules of dynamic modulus and phase angle are also discussed.

Abstract: Through tensile tests of shape memory alloy(SMA) wires, bars and plates, this paper analyzes hysteretic energy-dissipating capacities of these smart SMA materials in cyclic loading conditions. According to the test results, this article demonstrates the influence on energy dissipating capacity of SMA wires, bars and plates by different strain amplitudes, loading frequencies, cyclic numbers and pre-strains, then obtains change rules of hysteretic energy-dissipation. The test results show that the SMA wires is better than the other two SMA bars and plates, the SMA wires, bars and plates had better to be training before civil engineering application.

Abstract: In order to investigate the influence of loading frequency on the fatigue behaviors of the high strength steel, ultrasonic fatigue tests were carried out for a high-carbon-chromium steel and the results were compared with those of fatigue tests using conventional rotary bending fatigue test machine with a frequency of 52.5Hz. The different of fatigue strength at ultrasonic frequency level and conventional frequency level is very small and the S-N curve obtained from 20 kHz or 52.5 Hz shows the step-wise shape. The fatigue crack occurred from inclusions on the subsurface site in the long life regime and the typical surface fracture occurred in the short life one though the loading frequency level is different. It is indicated that ultrasonic fatigue method is an effective method to investigate the fatigue properties in super-long life region.

Abstract: James performed a series of experimental study on austenitic stainless steels and suggested an equation for assessing the influences of temperature, stress ratio and loading frequency on the fatigue crack growth rate. Authors have studied the effect of either loading frequency alone or of temperature alone on the fatigue crack growth rate by employing the mechanical behaviors of material. In this study, the mechanical behaviors of material are employed for evaluating the combined effect of loading frequency and temperature. Using the derived dimensionless functions of yielding stresses and Young’s modulus, the equation represented the combined effect of loading frequency and temperature on fatigue crack growth rate of 304SS was proposed.

Abstract: Titanium alloy matrix composites (TMCs) have received considerable interest as structural materials for aeronautical applications, because of their higher specific strength and stiffness. When applying TMCs at elevated temperatures, high temperature isothermal low-cycle fatigue (LCF)failure is one of critical issues to be concerned. A unidirectionally reinforced SCS-6/ SP-700 composite is a tentative target in this work, where the matrix alloy, SP-700 is a new generation high strength Titanium alloy developed by NKK Inc., and the SCS-6 is a beta-SiC fiber developed by Textron Specially Materials, respectively. A merit to employ the SP-700 is that this alloy enables to reduce a fabrication temperature, because of its capability for superplasticity at relatively lower temperatures. The 7-plies composite specimen was produced by hot isostatic pressing (HIP) at 800°C for 0.5 hrs. in vacuum, alternating layers of thin-foils of the SP-700 and the green tapes of the SCS-6 fibers, so that the fibers were uniformly distributed as a hexagonal array in the matrix. The volume fraction of the fibers in the composite is about 28 %. In this work, the following articles in a unidirectionally reinforced SCS-6/SP-700 composite have been studied and evaluated: (i)mechanical properties of the SCS-6/SP-700 composite and the matrix alloy at temperatures ranged between room temperature and 450°C; (ii) LCF lives and the failure modes of the composite and the matrix alloy at room temperature and 450°C; (iii) fiber push-out tests at elevated temperatures ranged between room temperature and 600°C, to represent the fiber/matrix interfacial strength; and (iv) observation and the characterization of the interfacial reaction zone by means of a transmission electron microscope (TEM) and an energy dispersive X-ray spectrometer (EDS). Based on these experimental results, the effects of temperature and the loading frequency on LCF failure of the SCS-6/SP-700 composite were discussed.