Numerical simulation and experimental study on laser hardening process of the 42CrMo4 steel

The large diameter pitch bearing was made of steel 42CrMo4 and the laser hardening process was used to improve its surface properties. In this paper, a numerical approach which can predict the temperature field and the hardened depth is provided for the laser hardening process of the 42CrMo4 steel. According to the simplification of the raceway structure of pitch bearing, the finite element model was constructed using ABAQUS software. Based on the actual process parameters, the transient thermal analysis was accomplished and the distribution of temperature field is analyzed. The hardened depth is determined according to the proposed temperature range. Laser power, laser scanning speed, and spot diameter were considered as input parameters, the experimental studies were performed based on orthogonal design in order to study the effects of process parameters. The finite element model is validated. The surface roughness and microstructure studies on treated surfaces were conducted. Also the micro-hardness testing was performed. The results show that the laser hardening increases surface hardness by about 3.8 times than that of the base material. The three parameters of laser power, laser scanning speed, and spot diameter have a coupling effect on the surface treatment. The input laser power density is more important.

Performance and Loads of a Lift Offset Rotor, Part II: Prediction Validations with Measurements

The predictions of an upgraded UMARC comprehensive analysis are compared to experimental lift offset rotor results. The experiments cover a range of collective pitch angles (θ°) from 2° to 10°, advance ratios (μ) from 0.21 to 0.53, and lift offset from 0% to 20%. The experimental model rotors are from a system of coaxial hingeless rotors, with two blades each, and a first flap frequency of approximately 1.6/rev. The simulation is compared with isolated rotor performance and controls with lift offset, loads, and pitch link forces. Increasing efficiency with increasing lift offset, the impact of lift offset on different loads, and the dependence of pitch link loads on pitch bearing damping are identified in the experiment and correlated with the simulation.

The double life of language systems: Modelling sonority with complementary symbol and signal based models

Sonority is a fundamental notion in phonetics and phonology, central to many descriptions of the syllable and evidently useful as a predictor of phonotactics (i.e., the propensity of different consonants and vowels to combine via concatenation). Although widely-accepted, sonority lacks a clear basis in speech articulation or perception, and traditional sonority principles exhibit gaps in empirical coverage, while they are also not designed to be compatible with general cognitive capacities. Against the backdrop of traditional sonority accounts, which have been exclusively based on discrete and symbolic machinery to model sonority, we propose an incorporation of symbol-based and signal-based models to adequately account for sonority with two complementary models. We claim that sonority is primarily a perceptual phenomenon related to the strength and quality of pitch perception, postulating a universal drive to optimize syllables as pitch-bearing units. We suggest a measurable acoustic correlate for sonority in terms of periodic energy, and we provide a novel principle that can account for syllabic well-formedness based on principles of competition in real-time; the Nucleus Attraction Principle (NAP). We present two perception experiments that test our two NAP-based models against four traditional sonority models and we use a Bayesian data analysis approach to test and compare the different sonority models. We show that our two NAP models retain the highest degree of complementarity while one of them is clearly superior to all the other models we tested. We interpret the results as providing strong support for our proposals: (i) the designation of periodic energy as sonority's correlate; (ii) the incorporation of continuity in phonological models, and; (iii) the dual-model strategy that separates and integrates symbol-based top-down processes and signal-based bottom-up processes.