WRINKLE LIMIT BLANK HOLDER FORCE MODELS IN SQUARE-BOX DEEP DRAWING WITH VARIABLE SEGMENT BLANK-HOLDERS

Constituting the reasonable control models of the wrinkle limit blank holder forces is the sticking point of the processes of the deep drawing with variable blank-holder forces, especially in the square-box forming. To begin with, a mode of segmenting flange of the square-box into eight zones is put forward according to the fact that the uniformity of flange deforming can be improved by control-ling segment blank-holders. Considering the integral influence of shear stress, a new concept, strain relaxation factor is defined. Hereby, the law of distribution of stress and stain in the deforming flange of square-box is achieved. Then based on these mechanical analysis models and the energy principle, the wrinkling flexivity functions of the straight flange and the circle flange are given, and the corresponding formulae of wrinkling limit blank-holder force in these two situations are also educed. In these processes, ply-anisotropy, strain hardening, thickness and friction are considered. In the end, a calculating example is designed to validate the rationality of the formulae of wrinkling limit blank-holder force, at the same time, the influences of the ply-anisotropy exponent and the strain hardening exponent on the wrinkle limit blank holder forces are also analyzed.

Upper bound limit analysis of roof collapse in shallow tunnels with arbitrary cross sections under condition of seepage force

The analytical solutions for predicting the exact shape of collapse mechanisms in shallow tunnels with arbitrary excavation profiles were obtained by virtue of the upper bound theorem of limit analysis and variation principle according to Hoek-Brown failure criterion. The seepage force was included in the upper bound limit analysis, and it was computed from the gradient of excess pore pressure distribution. The seepage was regarded as a work rate of external force. The numerical results of roof collapse in square and circular tunnels with different rock parameters were derived and discussed, which proves to be valid in comparison with the previous work. The influences of different parameters on the shape of collapsing blocks were also discussed.

The Implementation Mode of No-Fly Zones in International Relations

A No-Fly Zone(NFZ)is a unique mode of humanitarian intervention which is understudied in international relations.This article focuses on the political dimension of NFZs in international relations and investigates their implementations by empirically reviewing all three cases of NFZs to date.There may be efforts by intervening states to highlight humanitarian crises among certain targets to secure UN authorization for the NFZs;yet the implementation of NFZs is also driven largely by the security interests of enforcing states.As a result,there is the potential for those states implementing NFZs to transcend legal authorization and sometimes use excessive force,with likely calamitous results for local populations,or in extreme cases,accomplishing regime change by supporting opposition parties in target states.

Modeling limit force capacities of high force to volume lead extrusion dampers

Lead extrusion dampers are supplemental energy-dissipation devices that are used to mitigate seismic structural damage.Small volumetric sizes and high force capacities define high-force-to-volume(HF2V)devices,which can absorb significant response energy without sacrificial damage.However,the design of such devices for specific force capacities has proven difficult based on the complexities of their internal reaction mechanisms,leading to the adoption of empirical approaches.This study developed upper-and lower-bound force capacity estimates from analytical mechanics based on direct and indirect metal extrusion for guiding design.The derived equations are strictly functions of HF2V device geometric parameters,lead material properties,and extrusion mechanics.The upper-bound estimates from direct and indirect extrusion are denoted as(F_(UB,1),F_(UB,2))and(F_(UB,3),F_(UB,4)),respectively,and the lower-bound estimates are denoted as(F_(LB),F_(LB,1))based on the combination of extrusion and friction forces.The proposed models were validated by comparing the predicted bounds to experimental force capacity data from 15 experimental HF2V device tests.The experimental device forces all lie above the lower-bound estimates(F_(LB),F_(LB,1))and below the upper-bound estimates(F_(UB,1),F_(UB,2),F_(UB,4)).Overall,the(F_(LB),F_(UB,2))pair provides wider bounds and the(F_(LB,1),F_(UB,4)/F_(UB,1))pair provides narrower bounds.The(F_(LB,1),F_(UB,1))pair has a mean lower-bound gap of 36%,meaning the lower bound was 74%of the actual device force on average.The mean upper-bound gap was 33%.The bulge area and cylinder diameter of HF2V devices are key parameters affecting device forces.These relatively tight bounds provide useful mechanics-based predictive design guides for ensuring that device forces are within the targeted design range after manufacturing.