Surface Flaws (surface + flaw)

Distribution by Scientific Domains


Selected Abstracts


Effect of shot peening on fatigue limit of surface flawed samples

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3-4 2008
F. TAKAHASHI
ABSTRACT The effects of shot peening on the fatigue limit of specimens having a semicircular notch of varied surface length, 2a, are investigated. In the case of un-peened specimens, the fatigue limit of specimens having a notch of a= 0.05 mm was equal to that of the un-notched specimens. However, the fatigue limit of a= 0.3 mm was 46% smaller than that of the un-notched specimens. On the contrary, in the case of peened specimens, the fatigue limit of a= 0.2 mm was equal to that of the un-notched specimens and furthermore, that of a= 0.3 mm was only 5% smaller than that of the un-notched specimens. Multiple non-propagating cracks were observed in peened specimens after fatigue testing. The stress intensity factor of the maximum non-propagating crack size corresponded to that of a= 0.2 mm notch. These results indicate that shot peening increases fatigue limit and decreases the likelihood that a surface flaw will result in failure. [source]


Numerical and experimental investigation of mixed-mode fracture parameters on silicon nitride using the Brazilian disc test

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2010
G. LEVESQUE
ABSTRACT Engineering applications of ceramics can often involve mixed-mode conditions involving both tensile and shear loading. Mixed-mode fracture toughness parameters are evaluated for applicability to ceramics using the Brazilian disc test on silicon nitride. Semi-elliptical centrally located surface flaws are induced on the disc specimens using Vickers indentation and compression loaded to fracture with varying levels of mode mixity. The disc specimens are modelled via 3D finite element analysis and all three modes of stress intensity factors computed along the crack front, at failure load. We present a numerical and experimental investigation of four widely used mixed-mode fracture criteria and conclude that the critical strain energy release rate criterion is simple to implement and effective for silicon nitride under mixed-mode conditions. [source]


Fatigue behaviour of duplex stainless steel reinforcing bars subjected to shot peening

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2009
E. REAL
ABSTRACT The influence of shot peening on the fatigue properties of duplex stainless steel reinforcing bars manufactured using both hot- and cold-rolled processes was studied. The S-N curves of the bars before and after the shot-peening process were determined, showing that shot peening improves the fatigue behaviour of the rebars. This improvement is essentially due to the introduction of a compressive residual stress field in the surface of the reinforcing bars, but also to the smoothing of the surface flaws and cold working generated during the manufacturing process. This improvement is much greater in the case of the hot-rolled bars, mainly as a result of their much higher ability for plastic deformation, whereas cold-rolled bars had a much higher hardness. A more severe peening action capable of promoting greater plastic deformation on the bar surface is judged necessary to improve the fatigue resistance of cold-rolled rebars. [source]


Preliminary study of the crack healing and strength recovery of Al2O3 -matrix composites

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2004
L. JUN
ABSTRACT This study focused on the crack-healing behaviour of three commercial Al2O3,ceramic-matrix composites: TiCP/Al2O3, ZrO2/Al2O3 and SiCW/Al2O3. Vickers indentation was used to introduce surface flaws with different loads of 49, 98 and 196 N. Then the cracked specimens were annealed in air for 1 h at 1000, 1200 and 1400 °C. The annealing treatment was also conducted at 1200 °C in vacuum for 1 h. Results showed that the annealing treatments increased the indentation strength, but the extent of the increase was different. When annealed in air, the main crack-healing mechanism of TiCP/Al2O3 and SiCW/Al2O3 composites was chemical reaction. When annealed in vacuum, stress relaxation caused much less strength recovery. The main crack-healing mechanism of ZrO2/Al2O3 was the existence of low melting eutectic and the rearrangement of grains caused by ZrO2(m), ZrO2(t) transformation in the crack-opening process zone. The effects of annealing temperature, atmosphere and indentation load on the degree of strength recovery were all related to the crack-healing mechanisms. [source]


Manufacturing, mechanical characterization, and in vitro performance of bioactive glass 13,93 fibers

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2006
E. Pirhonen
Abstract Fibers were manufactured from the bioactive glass 13,93 by melt spinning. The fibers were further characterized by measuring their tensile and flexural strength, and their in vitro performance was characterized by immersing them in simulated body fluid, which analyzed changes in their mass, their flexural strength, and surface reactions. The strength of glass fibers is highly dependent on fiber diameter, test method, and possible surface flaws, for example, cracks due to abrasion. In this study, the thinnest fibers (diameter between 24 and 33 ,m) possessed the highest average tensile strength of 861 MPa. The flexural strength was initially 1353.5 MPa and it remained at that level for 2 weeks. The Weibull modulus for both tensile and flexural strength values was initially about 2.1. The flexural strength started to decrease and was only ,20% of the initial strength after 5 weeks. During the weeks 5,40, only a slight decrease was detected. The flexural modulus decreased steadily from 68 to 40 GPa during this period. The weight of the samples initially decreased due to leaching of ions and further started to increase due to precipitation of calcium phosphate on the fiber surfaces. The mass change of the bioactive glass fibers was dependent on the surface area rather than initial weight of the sample. The compositional analysis of the fiber surface after 24 h and 5 weeks immersion did confirm the initial leaching of ions and later the precipitation of a calcium phosphate layer on the bioactive glass 13,93 fiber surface in vitro. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]