Papers by Keyword: Cyclic Fatigue

Abstract: The aim of this study was to analyze the flexural strength of ceramics based on yttria-stabilized zirconia (YTZP) , used in the manufacture of dental prostheses infrastructure before and after aging with cyclic fatigue in moisture. The samples were made by pre-sintered blocks of ZirkonTransluzent (Zirkonzahn GMHB) from YTZP ceramics with and without feldspathic ceramic coating, divided into groups: G1 = YTZP control; G2 = YTZP aged; G3 = YTZP + feldspathic; G4 = YTZP + aged feldspathic. The samples were submitted to a three-point bending test with a speed of 0.5 mm / min. The mean values of the flexural strength values were G1 = 645 MPa (DP ± 124), G2 = 681 MPa (DP ± 129), G3 = 904Mpa (DP ± 157) and G4 = 954Mpa (DP ± 243). The values of groups G1 and G2; G3 and G4 were statistically similar, depending on the presence or absence of coating. Cyclic stresses did not affect the flexural strength of the material

Abstract: Abstract. To characterize the thermomechanical cyclic response, especially Pseudo-elastic behavior of NiTi shape-memory alloy (SMA) at different temperatures and different loading frequencies, a series of tests of both quasi-static and dynamic uniaxial compression cyclic loading have been performed on cylindrical samples, using an Instron servohydraulic testing machine and the Hopkinson technique. Transformation temperature, after dynamic loading is measured and compared with that of as-received state. The influence of the annealing temperature on the fatigue response is also examined. A few noteworthy conclusions are as follows: (1) Transformation temperature, can be changed under higher strain rates; (2) By changing the annealing temperature, the transformation stress and the dissipated energy of NiTi can also be obviously changed, so as it changes the transformation temperature, Af ;(3) In cyclic loading, the dissipated energy over cycles tends to be a minimum stable value, and it seems that cyclic loading leads to a stable Pseudo-elastic behavior of the alloy; (4) Repeated impact tests of the alloy produce slightly changes in the shape of the Pseudo-elastic loop and in the dissipated energy comparing with the quasi-static cyclic tests.

Abstract: The paper presents the concept of division of the total strain amplitudes. Simulations were performed for high-alloy steel X6NiCr3220 for proposing a new curve of cyclic strain based on the best fit to the experimental points and plotted the hysteresis loop. Proposed allocation of the total strain amplitude in three parts: the plastic strain amplitude, strain amplitude and the amplitude of the linearly elastic strain coupled. In order to preserve the forms of popular formula Ramberg-Osgoda and Manson-Coffin-Basquin modified them in such a way that added to their member responsible for the description of the coupled strain. Inclusion of additional term leading to closer representation of the actual material properties.

Abstract: The residual stress profile in a shot-peened Al alloy component was studied by a recently proposed method based on the known procedure of progressive thinning and X-ray Diffraction measurements. The effect the cyclic stress on the fatigue life was studied in detail, showing the correlation between nominal load and residual stress relaxation. Besides showing the expected decrease of compressive stress with the load and number of cycles, the present work highlights the importance of changes in the through-the-thickness residual stress distribution.

Abstract: In this research paper, the cyclic stress amplitude controlled fatigue response and fracture behavior of an Al-Cu (Aluminum Association designation 2219) is presented and discussed. The alloy was provided as a thin sheet in the T62 temper in the fully anodized condition. A small quantity of the as-provided sheet was taken and the surface carefully prepared to remove the thin layer of anodized coating. Test specimens of the alloy, prepared from the two sheets (anodized and non-anodized), were cyclically deformed under stress amplitude control at two different load ratios with the primary objective of establishing the conjoint influence of magnitude of cyclic stress, load ratio and intrinsic microstructural effects on cyclic fatigue life and final fracture characteristics. The high cycle fatigue resistance of the alloy is described in terms of maximum stress, load ratio, and microstructural influences on strength. The final fracture behavior of the alloy sheet is discussed in light of the concurrent and mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the alloy microstructure, magnitude of cyclic stress, and resultant fatigue life.

Abstract: In this research paper, the cyclic stress amplitude controlled fatigue response and fracture behavior of an Al-Cu-Mg alloy (Aluminum Association designation 2024) is presented and discussed. The alloy was friction stir welded in the T8 temper to provide two plates one having high tensile ductility and denoted as Plate A and the other having low tensile ductility and denoted as Plate B. Test specimens of the alloy, prepared from the two plates, were cyclically deformed under stress amplitude control at two different load ratios with the primary objective of documenting the conjoint influence of magnitude of cyclic stress, load ratio and intrinsic microstructural effects on cyclic fatigue life and final fracture characteristics. The high cycle fatigue resistance of the alloy is described in terms of maximum stress, R-ratio, and microstructural influences on strength. The final fracture behavior of the friction stir welded alloy is discussed in light of the concurrent and mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the alloy microstructure, magnitude of cyclic stress, and resultant fatigue life.

Abstract: This study presents the results of mechanical tests of commercial 2D SiCf/SiC ceramic matrix composite for fusion reactors applications. The creep behaviour was investigated by means of flexural constant load stress-rupture tests, in controlled atmosphere at 600 and 1000°C. The creep strain and time to failure vary with applied load according to a power law. Cyclical tests at room temperature and at high temperature showed that the material has a good fatigue behaviour at room temperature, as no evident fatigue damage was detected after 80.000 cycles at a peak load up to 98 % of MOR. Conversely at high temperature (1000°C) the specimens showed a progressive compliance increase and limited cycles to failure even at peak load as low as 40 % of MOR. Creep phenomena seem to influence the fatigue behaviour. Creep strain analysis, crack growth and fracture surface observations allowed to investigate the mechanisms that affect the crack propagation, the fracture process and the rupture life under cyclic loading and under constant stress loading at different temperatures.

Abstract: A compliance function is used to quantify the shielding capacity of grain bridging, the degradation of which is the main cyclic fatigue mechanism in alumina. Materials with different grain sizes were processed and the fatigue experiments were performed using the double torsion test. Significant degradation is observed in the coarse grain material and a marked sensitivity to the loading level is outlined. At moderate loads, bridging degradation occurs prior to fatigue crack growth during an incubation period. At low cyclic loads, the shielding capacity can be entirely degraded, leading to a cyclic fatigue threshold equivalent to that of the fine grain material.

Abstract: The torsion property and rotary fatigue fracture behavior of SmartÒ K file and R reamer made of nickel titanium alloy have been studied by means of Shimadzu Autograph DDS-10T universal tester and man-made cyclic system with curved copper tubes as simulated root canal. The instrument surface and the cyclic fatigue fracture surface have been investigated by optical microscope and scanning electron microscope. Comparing with ANSI/ADA specification no.28, maximum torsion values of both SmartÒ K and R endodontic instruments are satisfied in practice. Tensile stresses on the outer surface of the endodontic instruments play a dominant role in fracture initiation during cyclic fatigue fracture. The cyclic number corresponding to cyclic fatigue fracture decreases with the increase of the instrument size number/ curvature. SmartÒ K- and R endodontic instruments exhibit good ductility characteristics, therefore superior resistance to fracture.