The present study evaluates ratcheting response of 304 stainless steel samples subjected to various step-loading conditions at room and elevated temperatures through use of the kinematic hardening rules of Ohno-Wang (O-W), AbdelKarim-Ohno (AK-O) and Ahmadzadeh-Varvani (A-V). The hardening rules were employed along with visco-plastic flow rule to account for time-dependent response of 304 stainless steel samples. Ratcheting over Low-High-Low loading sequences consistently showed a small drop in ratcheting strain over the third loading step. This is mainly due to plastic strain accumulation over the first two loading steps preventing ratcheting strain to drop significantly with drop in mean stress. Moreover, dynamic recovery terms in these models were further modified through inclusion of an exponential function developed by Kang to address dynamic strain aging phenomenon. Progressive ratcheting response and their stress-strain hysteresis loops were highly influenced at various operating temperatures, stress levels, and stress rates. Coefficients in the dynamic recovery term of the A-V model controlled ratcheting progress and hysteresis loops agreeable with those of experimental data over consecutive loading steps. Choices of material constants and number of segments defined from stress-strain curve based on the O-W and AK-O models noticeably influenced ratcheting response of steel samples. Predicted ratcheting values by means of the A-V, O-W and AK-O models were discussed and compared with those of experimental data.

Instrumented indentation tests provide an attractive means for obtaining data to characterize the plastic response of engineering materials. One difficulty in doing this is that the relation between the measured indentation force versus indentation depth response and the plastic stress-strain response is not unique. Materials with very different uniaxial stress-strain curves can give essentially identical curves of indentation force versus indentation depth. Zhang et al. (J. Appl. Mech., 86, 011002, 2019) numerically generated “experimental” conical indentation data and showed that using surface profile data and indentation force versus indentation depth data together with a Bayesian-type statistical analysis permitted the uniaxial plastic stress-stress response to be identified even for materials with indistinguishable indentation force versus indentation depth curves. The same form of hardening rule was used in the identification process as was used to generate the “experimental” data. Generally, a variety of power law expressions have been used to characterize the uniaxial plastic stress-strain response of engineering materials and, of course, the form that gives the best fit for a material is not known a priori. Here, we use the same Bayesian statistics based analysis but consider four characterizations of the plastic uniaxial stress-strain response and show that the identification of the hardening rule parameters and the associated uniaxial stress-strain response is not very sensitive to the form of the power law strain hardening rule chosen even with data that has significant noise.

This study attempts to provide a theoretical estimate coupled with an analysis of the measured data to predict pitting damage of an aluminum alloy 2219 under the conjoint influence of mechanical load and corrosive environment. In accordance with the basic principle of crater growth coupled with the synergistic influences of mechanical and chemical effects, the law governing the presence and growth of corrosion pits was studied. Based on the concept of microscopic damage mechanics, porosity as a damage variable was introduced and the resulting model for estimating the reduction in elastic modulus of the material that has experienced observable damage due to pitting was established. Accelerated corrosion tests and uniaxial tensile tests are carried out, and a research-grade microscope coupled with a laser range finder was used to study the formation, presence, and growth of the pits with time. It was found that the corrosion pit in the chosen aluminum alloy can be simulated as a semi-ellipsoid, and the relationship between the depth of the pit and applied stress is an exponential function. This enabled in establishing the influence of alloy chemistry on nature, extent, and severity of damage due to pitting. The macroscopic morphology of the damaged specimens after corrosion was carefully observed and analyzed. The influence of time of exposure to the environment and applied load on damage due to pitting was verified. A comparison between the calculated results and experimental data reveals an overall correctness of the method developed and discussed in this paper.

Standard-compliant measurement of the in-plane fracture toughness of metals is often challenging due to insufficient material in the through-thickness direction to extract a full single edge bending (SEB) or compact tension (CT) fracture specimen. In the present work, we propose a new specimen design methodology to overcome this challenge. A W-shaped SEB specimen (called W-SEB) was developed, and its topology was optimized using finite element simulations. The new specimen design was validated numerically and experimentally on a case study showing excellent agreement with standard ASTM E1820 actual SEB specimen geometry. In view assessing the anisotropy of the fracture toughness (K Q and crack tip opening displacement (CTOD)) of pipeline steels susceptible to hydrogen-induced cracking (HIC), the W-SEB specimen was tested on X65 and X42 pipeline steel samples taken from the field. Experimental results show an increase in the maximum CTOD along the in-plane direction as compared to the transverse direction for both steel grades. Such experimental results could lead to important considerations with respect to accurate fitness for service assessment of HIC-damaged assets.

The present study intends to evaluate local ratcheting and stress relaxation of medium carbon steel samples under various asymmetric load levels by means of two kinematic hardening rules of Chaboche (CH) and Ahmadzadeh-Varvani (A-V). The Neuber's rule was coupled with the hardening rules to predict ratcheting and stress relaxation at the vicinity of the notch root. Stress-strain hysteresis loops generated by the CH and A-V models were employed to simultaneously control ratcheting progress over stress cycles and stress relaxation at notch root while strain range kept constant in each cycle. The higher cyclic load levels applied at the notch root accelerated shakedown over smaller number of cycles and resulted in lower relaxation rate. The larger notch diameter of 9 mm on the other hand induced lower stress concentration and smaller plastic zone at the notch root promoting ratcheting progress with less materials constraint over loading cycles compared with notch diameter d = 3 mm. Predicted ratcheting results through the A-V and CH models as coupled with the Neuber's rule were found in good agreements with the experimental data. The choice of the A-V and CH hardening rules in assessing ratcheting of materials was attributed to the number of terms/coefficients and complexity of their frameworks and computational time/central processing unit (CPU) required to run a ratcheting program.

In this study, parent aluminum (Al), silicon carbide (SiC) reinforced Al, zirconia (ZrO 2 ) coated SiC reinforced Al, and lithium zirconate spinel (Li 2 ZrO 3 , LZO) encapsulated SiC incorporated Al metal matrix composites were processed via friction stir processing (FSP) technique to observe the influence of grain refinement on mechanical and damping properties. Electron backscattered diffraction (EBSD) analysis were conducted for detailed and deep understanding of possible mechanism and microstructure at longitudinal cross sections of the samples. Further, the room temperature mechanical properties and thermal cyclic (−100 to 400 °C) damping performance of the friction stir processed composites were studied. The results obtained in this investigation show that storage modulus of pristine Al, SiC reinforced Al, ZrO 2 coated SiC reinforced Al, and LZO coated SiC reinforced Al were improved by a factor of 1.09, 1.17, 1.09, and 1.38, respectively, after FSP. Additionally, the ultimate tensile strength (UTS) and hardness of the friction stir processed SiC/Li 2 ZrO 3 /Al composite were improved by a factor of 1.08 and 1.11, respectively, after FSP was compared with an unprocessed composite.

In the present study, Ramor 500 armor steel plates were automatically welded using cold metal transfer arc welding (CMT), gas metal arc welding (GMAW), and hybrid plasma arc welding (HPAW) methods. To investigate the effects of three different fusion welding methods on metallurgical and mechanical properties, the welded joints were examined using optical microscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) and also subjected to radiographic, hardness, tensile, and notched impact tests. The weld metal (WM) region of the GMAW and HPAW joints consisted of massive austenite. In the CMT welded joint, the WM consisted mainly of dendritic austenite and a minor amount of δ-ferrite. Regardless of the welding process, the hardness of both the WM and heat-affected zone (HAZ) regions was found to be higher than the base metal (BM). The tensile strengths obtained by CMT, GMAW, and HPAW were 45%, 50%, and 65% of the BM, respectively. Cleavage-type brittle fractures occurred in the GMAW and HPAW welded joints, while localized ductile fractures occurred in the CMT joints. Tensile test specimens of the CMT joints fractured in the WM, while the GMAW and HPAW joints fractured in the HAZ. In terms of notch toughness, the CMT joints exhibited better impact resistance compared with the BM. GMAW and HPAW joints displayed less impact resistance than the BM, with values comparable with previous studies in the literature.