Limiting deformability and strength of basalt–plastic shells under internal explosive loading

The dynamic strength and deformability of basalt–plastic specimens under single pulsed (explosive) loading are studied experimentally. The results obtained show that the basalt–plastic specimens possess high specific strength and their strength characteristics are close to those of similar tubular specimens from glassreinforced plastic based on a highmodulus glass fiber. It is found that a twofold increase in all geometrical dimensions of the specimens does not affect their specific carrying capacity.     

Planar flow of a three-layer plastic material through a converging wedge-shaped channel. Part 1 – Analytical solution

Flow of a three-layer strip consisting of two different materials through an infinite converging channel is studied. Each material is assumed to be incompressible, rigid perfectly plastic. It is shown that the structure of the solution strongly depends on the ratio of the yield stresses and the friction factors, namely the problem may have the unique solution, multiple solutions, and may have no solution. This makes a significant difference between the new solution and other known solutions to the problem of flow through infinite channels.     

Double tube heat exchanger with novel enhancement: part I—flow development length and adiabatic friction factor

The study is conducted to evaluate the flow characteristics in a double tube heat exchanger using two new and versatile enhancement configurations. The novelty is that they are usable in single phase forced convection, evaporation and condensation. Correlations are proposed for flow development length and friction factor for use in predicting fluid pumping power in thermal equipment as well as in subsequent heat transfer characterization of the surface.     

Pressure drop measurements inside a flat channel – with flush mounted and protruding electrodes of variable length – using an electrorheological fluid

In this study the slit flow of an electrorheological (ER) fluid in an AC-field is studied with and without obstruction. Non-viscometric flow conditions are attained either by keeping the lengths of the electrodes short or by obstructing the flow via protruding electrodes. This latter condition seems to be beneficial, at least at low volume flow rates and short electrodes. Received: 5 November 1998 / Accepted: 7 July 1999     

The characteristics of plastic flow and a physically-based model for 3003 Al–Mn alloy upon a wide range of strain rates and temperatures

The uniaxial compressive responses of 3003 Al–Mn alloy upon strain rates ranging from 0.001/s to about 10⁴/s with initial temperatures from 77 K to 800 K were investigated. Instron servohydraulic testing machine and enhanced split Hopkinson bar facilities have been employed in such uniaxial compressive loading tests. The maximum true strain up to 80% has been achieved. The following observations have been obtained from the experimental results: 1) 3003 Al–Mn alloy presents remarkable ductility and plasticity at low temperatures and high strain rates; 2) its plastic flow stress strongly depends on the applied temperatures and strain rates; 3) the temperature history during deformation strongly affects the microstructure evolution within the material. Finally, paralleled with the systematic experimental investigations, a physically-based model was developed based on the mechanism of dislocation kinetics. The model predictions are compared with the experimental results, and a good agreement has been observed.     

Direct numerical simulation of flow over a forward-facing step – Flow structure and aeroacoustic source regions

A direct numerical simulation of the flow over a forward-facing step at a Reynolds number of 8000 based on the step height is presented. Calculations were performed using second-order finite volume discretisation in space on co-located meshes. A hybrid calculation approach based on Lighthill’s acoustic analogy is explained. Results of the simulation are intended to be used as a database for the validation of different discretisation schemes for the flow computation and simulation approaches for the calculation of sound radiation using a hybrid approach. Turbulent statistics are presented along with aeroacoustic source regions. Strong and weak forms of the aeroacoustic source term are presented and compared. For visualization purposes, the strong form is more suitable, whereas for the calculation of sound radiation both forms can be used. From the visualization of the aeroacoustic sources, it can be seen that they mainly concentrate on the region of the leading edge of the step and the shear layer close to the step.     

The generalized advancing conformal contact problem with friction,pin loads and remote loading – Case of rigid pin

The advancing, frictional contact problem for a rigid pin indenting an infinite plate with a circular hole is considered. The formulation is general, and considers remotely applied plate-stresses in addition to pin loads. Using the theory of generalized functions, it is found that the governing equation in full sliding is a singular integro-differential equation (SIDE). Partial-slip behavior is governed by an implicit, coupled singular integral equation (SIE) pair. Numerical solutions are presented for both types of problems. It is found that the contact tractions in monotonic loading become independent of the coefficient of friction above a certain threshold value. Finally, problems involving typical ‘fretting-type’ pin loads with and without remote-stresses are also investigated, revealing remarkable effects of the degree of conformality and load path on the steady-state traction distributions.     

Void fraction and pressure drop during external upward two-phase cross flow in tube bundles – part II: Predictive methods

The present paper is the Part II of a broad study concerning void fraction and pressure drop for air-water upward external flow across tube bundles. In the Part I, the experimental facility and the data regression procedures were described and the experimental results are presented and discussed. Initially, Part II presents a literature review concerning void fraction and pressure drop predictive methods available in the open literature for two-phase upward flow across tube bundles. Next, the methods from literature are compared among them and with the database presented in paper Part I. Significant discrepancies are observed among the predictive methods, and deviations as high as two orders of magnitude are verified among the predicted values of pressure drop. Then, a new void fraction predictive method is proposed based on the experimental results and on the minimum kinetic energy principle. This method provides satisfactory predictions of the results described in paper Part I and also of independent data from the literature. A new predictive method for frictional pressure drop during two-phase flow based on two-phase multiplier is also proposed. This method predicted 94% of the experimental data obtained in the present study within an error margin of ± 30%, and also provides accurate predictions of independent results for triangular tube bundles gathered in the open literature.     

Tension–torsion fracture experiments – Part II: Simulations with the extended Gurson model and a ductile fracture criterion based on plastic strain

An extension of the Gurson model that incorporates damage development in shear is used to simulate the tension–torsion test fracture data presented in Faleskog and Barsoum (2013) (Part I) for two steels, Weldox 420 and 960. Two parameters characterize damage in the constitutive model: the effective void volume fraction and a shear damage coefficient. For each of the steels, the initial effective void volume fraction is calibrated against data for fracture of notched round tensile bars and the shear damage coefficient is calibrated against fracture in shear. The calibrated constitutive model reproduces the full range of data in the tension–torsion tests thereby providing a convincing demonstration of the effectiveness of the extended Gurson model. The model reinforces the experiments by highlighting that for ductile alloys the effective plastic strain at fracture cannot be based solely on stress triaxiality. For nominally isotropic alloys, a ductile fracture criterion is proposed for engineering purposes that depends on stress triaxiality and a second stress invariant that discriminates between axisymmetric stressing and shear dominated stressing.     

Characterization of mechanical properties by indentation tests and FE analysis – validation by application to a weld zone of DP590 steel

In this work, the mechanical properties of the metal active gas (MAG) weld zone and heat affected zone (HAZ) were characterized utilizing the continuous indentation method together with its finite element (FEM) analysis. To verify the measured properties, uni-axial tension and three point bending tests were performed for DP590 welded specimens. For numerical simulations, the isotropic hardening law was assumed along with the non-quadratic anisotropic yield function, Yld2000-2d. As for the failure criterion of the base material and weld zones particularly for the failure evaluation in the uni-axial tension test, Hill’s bifurcation theory and the M–K theory were applied to calculate the forming limit diagrams considering all measured properties including strain-rate sensitivity.     

Comments on “Effects of temperature dependent fluid properties and variable Prandtl number on the transient convective flow due to a porous rotating disk by M. S. Alam,S. M. Chapal Hossain,M. M. Rahman [Meccanica (2014) 49:2439–2451]”

In this letter, we submit our comments on recently published paper titled “Effects of temperature dependent fluid properties and variable Prandtl number on the transient convective flow due to a porous rotating disk by Alam et al. (Meccanica 49: 2439–2451, 2014)”. Authors of this paper have attempted to present similarity solutions in the paper. We comment in this letter is that the similarity transformations considered in Alam et al. (Meccanica 49: 2439–2451, 2014) are not correct and thus results are leading to invalid conclusions.