Fatigue investigation at high load ratio R of a quenched and tempered chromium molybdenum steel

Abstract The fatigue behavior at high number of cycles in elastic-plastic field of quenched and tempered carbon chromium steel was experimentally investigated for high performance reciprocating compressors application. Fatigue tests on un-notched specimens were performed both under load and strain controls, by imposing different levels of stress/strain and for each of them different values of stress ratios R, especially high values. Stress and strain trends have been monitored, during the fatigue life, and either ratcheting or relaxation, respectively, was evident. The stress control tests have resulted into fatigue fractures only for low values of R with significant ratcheting and an increasing rate during the final part of the test, thus the fracture could be considered as a synergy between fatigue damage and plastic failure. On the contrary, the ratcheting stabilized for high values of R and the tests were finalized without any fracture. Within an intermediate region, for medium/high values of R, a minor ratcheting and the fracture transition have been found. Similarly, for the tests under strain control, low values of R showed fatigue fractures despite a considerable relaxation, conversely for high values of R, the relaxation was limited without any fracture. After reporting the tests on the Haigh plane, the Smith-Watson-Topper equation (SWT) provided the best prediction of the fatigue strength, at least until the intersection with the ultimate stress line, both under stress and strain control loadings. The cyclic behavior of the material was then investigated through several static and cyclic tests on plain specimens. A kinematic hardening Chaboche model, with three parameter couples, was proposed and the values of these parameters derived and discussed. Finally, other tests have been conducted on notched specimens with C geometry and blunt radius, again at high R values. FE analysis allowed the prediction of the stress evolution during the loading cycling, implementing the Chaboche model, and observing a combined effect of ratcheting and relaxation at the notch tip. The stabilized stresses were finally reported on the Haigh diagram and the results were found in agreement with the plain specimen fatigue line

Rapid and sound assessment of well-being within a multi-dimensional approach: The Well-being Numerical Rating Scales (WB-NRSs)

The assessment of well-being remains an important topic for many disciplines including medical, psychological, social, educational, and economic fields. The present study assesses the reliability and validity of a five-item instrument for evaluating physical, psychological, spiritual, relational, and general well-being. This measure uniquely utilizes a segmented numeric version of the visual analog scale in which a respondent selects a whole number that best reflects the intensity of the investigated characteristic. In study one, 939 clinical (i.e., diagnosed with cancer and liver disease with cirrhosis) and non-clinical (i.e., undergraduate students and their family and acquaintances) participants between the ages of 18 to 87 years (M = 47.20 years, SD = 19.62, 54% males) were recruited. Results showed items have strong discriminant ability and the spread of threshold parameters attests to the appropriateness of the response categories. Moreover, convergent and discriminant validity were found with other self-report measures (e.g., depression, anxiety, optimism, well-being) and the measure showed responsiveness to two separate interventions for clinical populations. In study two, 287 Canadian (ages ranged from 18 to 30 years; M = 20.78, SD = 3.32; 23% males) and 342 Italian undergraduate psychology students (age ranged from 18 to 29 years, M = 21.21 years, SD = 1.73, 38% males) were recruited to complete self-report questionnaires. IRT-based differential item functioning analyses provided evidence that the item properties were similar for the Italian and English versions of the scale. Additionally, the validity results obtained in study one were replicated and similar relationships between criterion variables were found when comparing the Italian- and the English-speaking samples. Overall, the current study provides evidence that the Italian and English versions of the WB-NRSs offer added value in research focused on well-being and in assessing well-being changes prompted by intervention programs

The illusion of replacement in research into the development of thinking biases: the case of the conjunction fallacy

The conjunction fallacy is a violation of a very basic rule of probability. Interestingly, although committing the fallacy seems irrational, adults are no less susceptible to the fallacy than young children. In Experiment 1, by employing tasks where the conjunctive response option involved two non-representative items, we found a large reduction in fallacy rates as compared to traditional conjunction fallacy problems. Nevertheless, fallacy rates remained relatively high in both adolescents and adults, although adults showed more consistency in their normative responses. In Experiment 2, we demonstrated that children’s relatively good performance on the task was not the consequence of their missing knowledge of social stereotypes. Additionally, children were more strongly affected by explicitly presented frequency information than adults. Indeed, adults only took frequency information into account when frequencies were made relevant by a training in probabilistic reasoning. Overall, the results suggest that whereas the potential for normative reasoning increases with development, this potential is often overshadowed by a pervasive tendency in adolescence and adulthood to rely on contextual information, knowledge, and beliefs, even when conflicting information is available. By contrast, children are more strongly influenced by explicitly presented information than relevant knowledge cued by the tasks.This research, and the writing of this paper, was partially supported by a UK Economic and Social Research Council post-doctoral fellowship [PTA-026-27-2989] to KM

Investigation of Chaboche and Bouc–Wen Parameters of Quenched and Tempered Steel and Comparison of Model Predictive Capabilities

The aim of this paper is to model the elastic–plastic uniaxial behaviour of a quenched and tempered steel. The common Chaboche isotropic kinematic hardening model (CIKH) is introduced, and a physics-based procedure is proposed to determine its parameters. This procedure is based on strain- and stress-controlled tests and is focused on the stabilized cycles. The imposed cycle properties are the hysteresis area, the stress range, the slope at the inversion points, obtained from the stabilized cycles of strain-controlled tests, and the ratcheting rate extracted from a stress-controlled test. The novelty of the algorithm is to determine the hardening parameters from the global properties of the cycle rather than imposing a pointwise fitting, which is also implemented to calculate the parameters for a comparison. The Bouc–Wen model showed great flexibility in describing nonlinear behaviours, corresponding to different physical phenomena, through an appropriate tuning of its parameter values. In this paper, another optimization approach is developed to estimate the Bouc–Wen coefficients and accurately describe the same experimental cycles. The performances of the Bouc–Wen model are compared with the predictions of the Chaboche model, and a discussion comparing the techniques used to reproduce cyclic plastic behaviour is provided