Amir Sultan

Numerical simulation and experimental verification of CMOD in SENT specimen: Application on FCGR of welded tool steel

Single-edged notched tension (SENT) specimen is used to study the fatigue crack growth rate (FCGR) behavior of AISI 50100 steel using MTS 810. Calibration tests are run to get plots of crack mouth opening displacement (CMOD) vs. load and CMOD vs. crack length-to-width ratio with the known crack lengths. Numerical simulation is also done to try to establish a relation between crack length and CMOD. FCGR of welded and un-welded specimens are plotted against stress intensity factor range to show the effect of welding on fatigue crack growth rate of AISI 50100 steel. The experimentally obtained CMOD values are compared with values obtained by numerical simulation using ABAQUS/Standard™ software package. Results show that numerical values are in good agreement with experimental data for small crack lengths and lower values of applied load.

An Investigation into the Fatigue Crack Growth Rate of Electron Beam-Welded H13 Tool Steel: Effect of Welding and Post-Weld Heat Treatment

Fatigue crack growth rate (FCGR) behavior of 3-point bend specimen of electron beam-welded AISI H13 tool steel is studied. Three types of specimens were studied here; specifically: the base metal, as-welded, and post-heat-treated welded samples. The crack length is measured visually as well as calculated using crack mouth opening displacement (CMOD) gage. The FCGR curves of different specimens are compared. The validity of using CMOD as a tool for indirect crack length measurement as per ASTM E399 is explored. Additionally, the possibility of using CMOD as a crack driving force parameter instead of stress intensity range (ΔK) is explored. It is shown that the CMOD is a better crack driving force parameter and the indirect crack length measurement is not a reliable tool, especially for welded specimens. In the end, CMOD versus crack length is numerically simulated by finite element analysis to give us a base line CMOD versus crack length without microstructural or plasticity effects.

Influence of electric discharge machining on fatigue limit of high strength aluminum alloy under finish machining

Abstract The aim of this study was to investigate the fatigue limit of the electric discharge machined aluminum alloy 2024 T6. Machining was performed at 3, 6, 9, and 12 A discharge current values while all other parameters were kept constant. The fatigue tests were performed on a four-point rotating bending machine at the frequency of 50 Hz and at ambient temperature. Fatigue limits at 107 cycles were determined using staircase (up-and-down) method and the obtained data was analyzed statistically. For reference purposes, fatigue strength of the conventionally turned specimens was also found by the same technique. The EDM surface is characterized by its morphology, roughness, hardness, and thickness of the resolidified layer. The effects of discharge current values on these surface characterizing parameters and subsequent influence on fatigue limit have been discussed.

Evaluation of Fatigue Behavior and Surface Characteristics of Aluminum Alloy 2024 T6 After Electric Discharge Machining

Abstract The effect of electric discharge machining (EDM) on surface quality and consequently on the fatigue performance of Al 2024 T6 is investigated. Five levels of discharge current are analyzed, while all other electrical and nonelectrical parameters are kept constant. At each discharge current level, dog-bone specimens are machined by generating a peripheral notch at the center. The fatigue tests are performed on four-point rotating bending machine at room temperature. For comparison purposes, fatigue tests are also performed on the conventionally machined specimens. Linearized SN curves for 95% failure probability and with four different confidence levels (75, 90, 95 and 99%) are plotted for each discharge current level as well as for conventionally machined specimens. These plots show that the electric discharge machined (EDMed) specimens give inferior fatigue behavior as compared to conventionally machined specimen. Moreover, discharge current inversely affects the fatigue life, and this influence is highly pronounced at lower stresses. The EDMed surfaces are characterized by surface properties that could be responsible for change in fatigue life such as surface morphology, surface roughness, white layer thickness, microhardness and residual stresses. It is found that all these surface properties are affected by changing discharge current level. However, change in fatigue life by discharge current could not be associated independently to any single surface property.

Fatigue Crack Growth Behaviour of AISI 50100 Precipitation Hardened Steel after Welding

Single-edged notched tension (SENT) specimen is used to study the fatigue crack growth rate (FCGR) behavior of AISI 50100 steel using MTS 810. Calibration tests are run to get plots of crack mouth opening displacement (CMOD) vs. Load and CMOD vs. Crack length to width ratio with the known crack lengths. FCGR of welded and un-welded specimens are plotted against stress intensity range to show the effect of welding on fatigue crack growth rate of AISI 50100 steel, initial results of the experimentation are presented.