Parametric Optimization of WEDM Characteristics on Inconel 825 using Desirability Research

The present research focuses on the optimization of wire-cut electric discharge machining (WEDM) parameters. In this study, RSM based multi-response desirability method is used to optimize the WEDM characteristics for single and multiple responses. Input parameters of WEDM viz. pulse-on time, pulseoff time, spark gap voltage, wire tension, peak current, wire feed and performance was measured in terms of material removal rate (MRR) and surface roughness (SR). WEDM is a nontraditional method uses the spark erosion principle to produce the intricate shape and profiles of difficult-to-cut material. Inconel 825 is increasing in demand in the aerospace industry for more heat resistant and tough material. Because of its robust nature, it is difficult to be machined with conventional methods. WEDM is best alternate to overcome this problem. It has been observed that at Ton 111 MU, Toff 35 MU, SV 46V, IP 140A, WT 9 MU and WF 6 m/min, the values obtained for MRR and SR are 32.015mm2/min and 2.528 μm respectively

Application of Differential Entropy in Characterizing the Deformation Inhomogeneity and Life Prediction of Low-Cycle Fatigue of Metals

The relation between deformation inhomogeneity and low-cycle-fatigue failure of T2 pure copper and the nickel-based superalloy GH4169 under symmetric tension-compression cyclic strain loading is investigated by using a polycrystal representative volume element (RVE) as the material model. The anisotropic behavior of grains and the strain fields are calculated by crystal plasticity, taking the Bauschinger effect into account to track the process of strain cycles of metals, and the Shannon’s differential entropies of both distributions of the strain in the loading direction and the first principal strain are employed at the tension peak of the cycles as measuring parameters of strain inhomogeneity. Both parameters are found to increase in value with increments in the number of cycles and they have critical values for predicting the material’s fatigue failure. Compared to the fatigue test data, it is verified that both parameters measured by Shannon’s differential entropies can be used as fatigue indicating parameters (FIPs) to predict the low cycle fatigue life of metal.

Mechanics and energetics of myosin molecular motors from nonpregnant human myometrium

Mechanical properties of spontaneously contracting isolated nonpregnant human myometrium (NPHM) were investigated throughout the whole continuum of load from zero load up to isometry. This made it possible to assess the three-dimensional tension-velocity-length (T-V-L) relationship characterizing the level of contractility and to determine crossbridge (CB) kinetics of myosin molecular motors. Seventy-seven muscle strips were obtained from hysterectomy in 42 nonpregnant patients. Contraction and relaxation parameters were measured during spontaneous mechanical activity. The isotonic tension-peak velocity (T-V) relationship was hyperbolic in 30 cases and nonhyperbolic in 47 cases. When the T-V relationship was hyperbolic, the Huxley formalism could be used to calculate CB kinetics and CB unitary force. At the whole muscle level and for a given isotonic load level, part of the V-L phase plane showed a common pathway, so that a given instantaneous length corresponded to only one possible instantaneous velocity, independent of time and initial length. At the molecular level, rate constants for CB attachment and detachment were dramatically low, ∼100 times lower than those of striated muscles, and ∼5 to 10 times lower than those of other smooth muscles. The CB unitary force was ∼1.4 ± 0.1 pN. NPHM shared similar basic contractile properties with striated muscles, reflected in the three-dimensional T-V-L relationship characterizing the contractile level. Low CB attachment and detachment rate constants made it possible to generate normal CB unitary force and normal muscle tension in NPHM, even though it contracted extremely slowly compared with other muscles.

Study on New Model of Tension Process in Continuous Rolling

It is proved that a tension peak occurred in the beginning of tension process between two stands by the continuous rolling test. Based on the speed difference, motor rigidity and coefficient of forward and backward slip, the steady equation of the kinematical mechanics is built. The simulation results of the tension formula accorded with the experimental data. The calculation of shock peak provides an important reference for the technology of continuous rolling.

Nonlinear summation of force in cat soleus muscle results primarily from stretch of the common-elastic elements

The complex connective tissue structure of muscle and tendon suggests that forces from two parts of a muscle may not summate linearly. This study measured the nonlinear summation of force (Fnl) in whole cat soleus during isometric and ramp movements. In six anesthetized cats, the soleus was attached to a servomechanism to control muscle length and record force. The ventral roots were divided into two bundles, each innervating about half the soleus; thus the two parts could be stimulated alone or together. In all experiments, Fnl was small (<6% of maximum tetanic tension). Peak Fnl occurred during changes in muscle force, either as a result of imposed muscle movement or the onset or offset of a stimulus train. The data were fit to a model in which both parts of the muscle were assumed to stretch to a common elasticity. The servomechanism was programmed to compensate for reduced stretch of the common elasticity during partial compared with whole muscle activation. These compensatory movements showed how the model could account for most, but not all, of Fnl.

Dynamic stiffness of rabbit mesotubarium smooth muscle: effect of isometric length

The dynamic stiffness of mesotubarium smooth muscle from nonpregnant adult rabbits was measured continuously during isometric contraction by applying small (0.5 percent of the muscle length) sinusoidal length perturbations and measuring the amplitude and phase of the resulting tension perturbations. Stiffness during contraction was directly proportional to muscle tension; during relaxation stiffness at all tensions was significantly increased as compared to the values encountered during the rise of tension. Peak isometric tension and dynamic stiffness (determined at a common tension level) both decreased at shorter muscle lengths; the relative falloff in stiffness was significantly less than the tension decrease. Varying levels of muscle activation (obtained by changing stimulus strength and by applying quick releases to active muscle) had little effect on the measured elastic modulus. Comparisons of these results with published data on single-cell contractile properties imply a cellular locus for a portion of the measured stiffness.

Increased dynamic stiffness of trabeculae carneae from senescent rats

Dynamic stiffness was measured in both adult and senescent Wistar rats using sinusoidal length perturbations from 17 to 40 Hz, superimposed on isometric contractions at low and below Lmax. The slope of the stiffness-tension relationship was found to be increased in senescent muscles of both sexes and at two different temperatures. The age dependence of the slope was independent of resting muscle length. The slope also exhibited frequency dependence and hysteresis that indicates the presence of viscoelasticity during activation. No age dependence was seen in peak active tension, peak dT/dt, or resting stiffness. The findings of this study, taken together with other studies that have shown a decreased shortening ability in the senescent muscle, explain in part the maintenance of active tension development in the face of decreased shortening ability associated with the senescent muscle.

Frog Fast Muscle

1. The paper is primarily concerned with predicting the response of the muscle (frog ilio-fibularis fast fibres) to a given stimulus under given conditions of load. The predictive value of theories based on ‘active state’ is considered in this context. 2. A method is described for measuring the speed of shortening at frequent intervals during an isotonic twitch. 3. A family of speed vs. tension curves is drawn up, each curve representing a particular time after the stimulus. These are translated into power vs. tension curves. 4. The rate of fall of mechanical power output increases linearly with time after the stimulus, but is independent of tension. 5. At the beginning of the twitch, mechanical power output increases slightly with temperature, but later in the twitch the trend is reversed, as rate of fall of power also increases with temperature. 6. The high extensibility, characteristic of resting muscle, reappears suddenly at the end of an isotonic twitch, causing a ‘break’ in the speed record. This occurs earlier at low than at high tensions. 7. The basis of predicting an isometric twitch from isotonic data, based on certain assumptions which have been made by previous authors, is explained. 8. The tension peak in an isometric twitch is reached sooner than would be predicted on these assumptions.