D. Webb

Prediction of cutting force distribution and its influence on dimensional accuracy in peripheral milling

Cutting force has a significant influence on the dimensional accuracy due to tool and workpiece deflection in peripheral milling. In this paper, the authors present an improved theoretical dynamic cutting force model for peripheral milling, which includes the size effect of undeformed chip thickness, the influence of the effective rake angle and the chip flow angle. The cutting force coefficients in the model were calibrated with the cutting forces measured by Yucesan [18] in tests on a titanium alloy, and the model was proved to be more accurate than the previous models. Based on the model, a few case studies are presented to investigate the cutting force distribution in cutting tests of the titanium alloy. The simulation results indicate that the cutting force distribution in the cut-in process has a significant influence on the dimensional accuracy of the finished part. Suggestions about how to select the cutter and the cutting parameters were given to get an ideal cutting force distribution, so as to reduce the machining error, meanwhile keeping a high productivity.

Finite-element modelling of the impact response of a laminated composite plate

An investigation into the response of a fibre-reinforced composite plate subjected to a central impact by a blunt-ended projectile, shows that coupling between the dynamic response and the stiffness degradation due to damage must be accounted for in any model capable of predicting damage by impact. A numerical model based on the finite-element displacement method that includes the effects of transverse shear deformation and a failure algorithm that describes the energy dissipation during the damage process has been developed for the purpose of the analysis. The interaction force between the projectile and the plate is modelled as an integral part of the solution algorithm, thus neglecting the assumption of an initial contact-pressure profile. Numerical results for laminate deformation are shown to compare qualitatively well with experimental tests. Numerical values for stresses in the plate are computed and the effect of anisotropy on stress and deformation profiles are identified and discussed.

Large deflection analysis of multilayer cantilever beams subjected to impulse loading

Abstract A numerical study of the elastic–plastic response of multilayer cantilever beams to impulse loading is presented and compared with experimental results. The impulse loading from the experimental tests, which was obtained by subjecting stationary aluminium cantilever beams to high transient magnetic fields on the surface of the cantilever, was converted to pressure loading for the purposes of the numerical analysis. In addition to the elastic–plastic finite element model, an approximate theoretical model based on an energy method is developed. The combination of large deflections and elastic effects removes the restrictions imposed by the rigid-plastic theory, and provides the possibility for a better comparison with the data obtained from the experimental tests. Results from each of these approaches are compared with those from experiments. It is concluded that a non-linear, elastic–plastic transient analysis is needed to predict the deformation response resulting from the impulse loading of cantilever beams.

The influence of inertia and strain-rate on large deformation of plate-structures under impact loading

Abstract The static and dynamic behaviour of plate-structures subjected to in-plane axial and compressive impact loading is investigated using the finite element method (FEM). The material model is linear elastic with nonlinear isotropic work hardening characteristics with strain-rate dependence, inertia (via a consistent mass matrix) and geometrical nonlinearities are retained. The FEM results are in very close agreement with those obtained from experiments but the main advantage of the method is that it clarifies the time history behaviour of the model. The previous theoretical work has identified two distinct phases of deformation. Phase one is the compression of the plate, following the inelastic collision, until the structure becomes plastic. This is followed by a second phase of continuous plastic work dissipation in rotation about the hinges formed. The FEM results indicate the nature of the collision strain rate intensity and the differences that exist between static and dynamic modes of deformation response. The numerical modelling also reveals four phases in the deformation process. A phase of stress wave propagation is identified during elastic loading and the build up of high initial axial forces in the specimen. This is followed by a squashing phase, hinge rotation and elastic recovery (or, when the impact energy is high enough, structural closure) before the striker rebounds. The closure phase resembles a severe forming process followed by elastic recovery of the specimen and rebound of the striker. The differences between the various treatments are discussed and analysed in some detail.

“Truths” and “Re‐Imaging” in the Reconciliation Process

In this essay, we discuss the initial stages of an investigation into what we mean by truth and the role that truth plays in the reconciliation process. The attempt to re-image the past and uncover the truth surrounding human rights abuses after violent conflicts and political dictatorships is one of the central roles of the work of Truth Commissions. This is, of course, the reason why the word ‘‘truth’’ is included in the designation of many of the commissions created to investigate past human rights abuses and promote reconciliation. South Africa, for example, established the Truth and Reconciliation Commission; Chile, the National Commission on Truth and Reconciliation; and the Commission on the Truth for El Salvador was set up in El Salvador. Even in cases where the word is missing from the title, there may still be a requirement to investigate and report the truth about past abuses. In the case of Ghana, for instance, the National Reconciliation Commission was required primarily to establish an ‘‘accurate, complete historical record’’ of past human rights violations.

The application of the FEM to determine the response of a pretorsioned pipe cluster to static or dynamic axial impact loading

Abstract The FEM is employed to model the response behaviour of three identical thin tubes which are arranged so that the centres of their bases are positioned at the apices of an equilateral triangle. The effects of pretorsioning the cylinders and then applying static and dynamic loads are computed and presented. The cylinders in the model are firstly simultaneously subjected to an axial torque by the application of a uniformly distributed edge load at the upper circumference of each cylinder. The application of the torque to the system is implemented in the first solution step of the FEA in the absence of all other forces. The static or dynamic loads are applied in the second solution step. The static axial load is induced in the model by displacing the bases of the cylinders in the upward direction, while appropriately constraining their upper ends. For the application of the dynamic axial impact loading, a mass element is included in the model which is energised by an initial upward velocity. The subsequent load-deformation response modes are computed and discussed and compared with those obtained from a model which does not include pretorsioning. The system response modes, as revealed in this analysis, exhibit several novel features which have not been previously reported in the literature and which are the subject of close examination in this paper. Results are also presented from a more simplified model (using beam elements) of a three-legged platform subjected to similar loading conditions. In this case the load bearing characteristics of the system are shown to be dependent upon the angle that the legs make with the platform. The optimization of a system of this type, subject to these loading conditions, is discussed and demonstrated.

Projecting Ideas on a Perpetual Peace

The “Projecting Peace” project followed an international conference on “Imaging War,” sponsored by the European Science Foundation in 2008. It considered how the “imagers of war” can be viewed through a range of disciplinary lenses, and explored how organized knowledge systems, scenarios, and stories are used to legitimate war and its consequences. Some of the major contributions to the conference were published in Peace Review in 2009 and formed the basis for the thinking behind “Projecting Peace,” which was established to investigate how academics, activists, and practitioners (working as individuals or in groups or organizations) are researching, discussing, and working on peace projects.

(Un)Covering the Silence During the Argentinean Coup d'État

This essay examines the connection between the media, society, and human rights movements in Argentina during the last savage dictatorship that ruled that country between 1976 and 1983. During the socalled Dirty War (a term coined by the Argentinean military as an excuse to eliminate groups of a different political ideology), an estimated 30,000 people were killed, ‘‘disappeared,’’ kidnapped, and tortured. According to the CONADEP 2007 archives, there were denouncements of approximately 600 kidnappings before the coup d’état on March 24, 1976, and thousands of people were illegally deprived of their freedom. 8,960 are still missing.

Use of the FEM to study the thermal buckling of long beam-type structures

Publisher Summary This chapter investigates the elastic buckling of long and slender structures of infinite lateral extent that are supported on rigid and plane surfaces with a state of anisotropic Coulomb friction among the contacting surfaces. The method employed assumes that the material behaved in a linear elastic fashion and is accompanied by a nonlinear large-scale change in geometry. The solution scheme is implemented in three distinct separate steps. In the first step, the effects of the gravitational field are activated; in the second step, an imperfection is introduced into the geometry of the structure; and in the third step, an axial displacement is applied equivalent to the expansion of the pipe due to the rise in temperature. The buckling length is free to develop without any restrictions, allowing a progressive diminution of the axial force, due to frictional effects, throughout the solution phases. Coulomb friction can also be introduced differentiating among the slippage resistances in the axial or lateral directions. Preliminary results from a more complex coupled temperature-displacement analysis are also presented. The chapter also develops a theory based on a beam that is supported on an elastic foundation and includes the effects of friction by considering the governing equations for various segments, each segment having different contact conditions. The effects of temperature on the pipeline model are included by subjecting it to an axial displacement equivalent to the expansion produced by a change in temperature of the whole pipe.

A Novel Systematic Approach To Modeling Precision-machined SurfacesBased On Mathematical Transforms

In this paper, a systematic approach is proposed to modeling precision engineering surfaces. It attempts to consider all aspects of the machining process to obtain high quality surfaces. This approach integrates the inputs from machine tools, operation conditions, cutting tools and work materials with the surfaces machined as the output based on mathematical transforms. Wavelet transform, fiactal and chaos theory are used in the modeling. Preliminary research results show that the proposed approach and modeling techniques are very promising, albeit more research and machining trails are needed to further validate the approach.