Constant Force Conditions Research Articles

Unsteady Flow of Semi-Concentrated Fiber Suspensions in Compression Molding

Abstract This paper deals with the flow behavior and the resulting fiber orientation during compression molding of semi-concentrated fiber suspensions. The suspension is characterized using the Dinh and Armstrong integral constitutive relations, expressed in terms of the finite deformation tensors. The equations of motion are expressed in a convenient Generalized Eulerian-Lagrangian reference frame. The resulting nonlinear system of equations is solved using full Newton-Raphson iteration procedure. An integral boundary condition has been applied at the press wall to represent the constant force condition at that boundary. Results are presented for the isothermal filling of a two-dimensional rectangular cavity for the flow field and the associated fiber orientation. The influence of different parameters such as molding force, fiber concentration, fiber aspect ratio etc. on the compression rate is also presented.

An improved Non‐reflecting Boundary Method for Soil‐Structure Interaction Analysis

Abstract: For dynamic analysis of interaction between structure and soil foundation, the elimination of wave reflecting on the artificial finite element boundary of semi‐infinite body is an essential problem. In this paper, a non‐reflecting boundary method with constant acceleration and constant force applied at the boundary is presented. A Corresponding explicit‐implicit algorithm for dynamic analysis of the semi‐infinite body is given. A good agreement of solutions is obtained as compared with the generalized Smith non‐reflecting boundary method with constant velocity and constant boundary force conditions. But it is much easier to implement, arid the computational effort and the storage required are considerably reduced.

The determination of a general time creep compliance relation of linear viscoelastic materials under constant load and its extension to nonlinear viscoelastic behavior for the Burger model

Linear viscoelastic materials yield a creep function which only depends on time if creep experiments are performed under constant stress σ0. In practice, this condition is very difficult to realize, and as a consequence, the experiments are performed under constant force. For small strains the difference between the conditions of constant stress and constant force is negligible. Otherwise, the decrease in cross-section has to be taken into account and leads to increasing stress in the course of time for creep experiments under constant load. The Boltzmann superposition principle is solved under the condition of constant load and for strains \(\varepsilon (t) = \frac{{l(t)}}{{l_0 }} < 0.2\). The creep complicance C(t; σ0) defined by the ratio \(\frac{{\varepsilon (t)}}{{\sigma _0 }}\) becomes, in principle, dependent on the initial stress σ0. As a consequence, a set of creep compliance curves cannot be approximated with a simple parameter fit. Already the application of the solution on the Burger model yields a creep compliance curve with all three creep ranges. Furthermore, the mathematical structure of the time creep compliance relation of the Burger model allows nonlinear viscoelastic extension via the introduction of the yield strength σmax and a nonlinearity parameter n l . The creep behavior of PBT and PC can be described in the range of long times up to initial stresses σ0, being 75% for PBT and 60% for PC of the yield stress σmax with only two or one free fit parameter, respectively.

Molecular-dynamics study of elasticity and failure of ideal solids.

Results are presented from molecular-dynamics simulations of ideal solids under conditions of constant temperature, pressure, and uniaxial tensile force. We show that the system remains in metastable equilibrium all the way up to a critical value of the applied stress or force, at which point it fails irreversibly via the nucleation of small-scale defects. The critical load (failure strength) is found to decrease strongly with temperature.

On the multiple equilibrium of the development of tropical cyclone in nonlinear CISK model

By using non-static atmosphere equations including basic current, heating force and friction, we discuss the balance amplitude of vertical motion in the conditions of constant heating force, linear and non-linear interaction between large-scale ascending motion and diabatic heating force. In the non-linear condition, the multiple equilibrium feature of the tropical cyclone development is discussed and the reason of the sudden varying of tropical cyclone intensity is studied preliminarily.

Effect of learning on production of duration in variable motor conditions

It has been suggested that increasing proprioceptive feedback and ensuring its consistency from trial to trial favours timing accuracy. The progressive acquisition of a timing performance with isometric and anisometric responses was investigated in conditions of ‘inconsistent feedback’, with two different methods: counting seconds or not. Subjects gripped the handle of a dynamometer during precisely 5 seconds in 4 randomly distributed conditions: ‘Weak’ or ‘Strong’ constant force, ‘Slow’ or ‘Rapid’ variable force. A first group produced the durations without counting and a second group counted seconds either mentally or aloud. Learning was examined in 4 successive blocks of trials. Average produced durations did not differ as a function of group, but the variability was reduced when subjects counted seconds. In both groups, the constant force conditions induced more accurate responses than the variable force conditions in the first block of trials. ‘Slow’ and ‘Rapid’ conditions were respectively associated with overestimation and underestimation of response duration. These trends diminished progressively with learning. Both groups yielded sequential effects linked to duration and independent of condition. These data suggest that, whether subjects counted or not, learning was not based on condition-specific proprioceptive feedback. It may involve the elaboration of an internal temporal reference common to all conditions.

Effects of Boundary Conditions on the Stability of Slender Viscous Fibers

The one-dimensional isothermal flow of viscous-liquid fibers displays draw resonance instability when a constant-velocity winder condition is applied. This instability is removed when a constant-force condition occurs at the winder. The instability mechanism is examined and used to explain the stability trends when the effects of gravity, surface tension, inertia, and wind stress are included.

Features of the extensional flow of cellulose diacetate films in active media

The behaviour of cellulose diacetate films that had been previously oriented in ethanol has been studied during uniaxial extension in a water-phenol mixture under conditions of constant stress and constant force in the temperature range 40–60°C. Analysis of the flow curves obtained has enabled it to be concluded that the observed relationships may be explained in terms of a “negative extensional viscosity”, the internal source of which is apparently a mesophase formed in the material. A direct rheological method of measuring the “negative extensional viscosity” is proposed.

Steady-state performance characteristics of linear reluctance motors

Theoretical and experimental results are presented for the performance of a linear reluctance motor with a ratio of airgap to pole pitch appropriate for urban transport applications. Results are given for conditions of constant current, voltage, flux or normal force; it is shown that the machine could be used for combined propulsion and magnetic suspension of a vehicle.

The charge on edge dislocations in pure KBr single crystals

Abstract The charge on moving edge dislocations in pure KBr single crystals has been investigated, using two different vibration methods. The smallest charge detected was about 2% of the maximum that can be accommodated on the edge dislocation. This charge increases at increased vibration amplitudes. Prolonged vibration under constant force conditions reveals a long-term decrease of the dislocation charge, which could be distinguished from an apparent decrease, due to a short-and a long-term decrease of the micro-plastic strain amplitude. The oscillating dislocation probably loses some of its extra charge to the redistributed Debye-Huckel charge cloud.