37 research outputs found
Adhesive joint geometry variation in non-rigid aircraft structures
Adhesive bonding is a proven alternative to mechanical fasteners for structural
assembly, offering lighter and thus more fuel efficient aircraft and cost-effective
manufacturing processes. The effective application of bonded structural
assemblies is however limited by the tight fit-up requirement, which is with
tolerance ranges of hundreds of microns; this can be a challenge for the industry
to meet considering the variability of current part manufacturing methods and the
conservative nature of the conventional tolerance stack-up analysis method.
Such a (perceived) limitation can discourage effective exploitation of bonding
technologies, or lead to development of overengineered solutions for assurance.
This work addresses such challenge by presenting an enhanced bondline
thickness variation analysis accounting for part deflection of a bonded skinstringer assembly representing a typical non-rigid airframe structure. A semianalytical model accounting for unilateral contact and simplified 1D adhesive flow
has been developed to predict bondline thickness variation of the assembly given
the adherends’ mechanical properties, adhesive rheological properties, and
external assembly forces or boundary conditions. A spectral-analysis method for
assembly force requirement estimation has also been tested. The bondline
dimensions of several representative test articles have been interrogated,
including a reconfigurable test assembly designed specifically to test the input
conditions that affect bondline geometry variation. It has been demonstrated that
the part deflections need to be accounted for regarding the fit-up requirement of
bonded non-rigid structural assembly. The semi-analytical model has been found
to more reliable and realistic prediction of bondline thickness when compared to
a rigid tolerance stack-up. The analysis method presented can be a major
technology enabler for faster, more economical development of the aircraft of the
future, as well as of any analogue structures with high aspect ratios where weight
savings and fatigue performance may be core objectives.Aerospac
An Equilibrium Bid Markup Strategy
Setting a bid markup strategy is a very difficult task. Nevertheless, it is important to construction firms or consulting engineering companies because the development of successful bidding strategies is a key factor to their survival in business. Based on the two bidding criteria of the conditional profit ratio and the work force continuity, this short paper first presents the explicit expression of an equilibrium bid markup strategy in procurement auctions. However, the two bidding criteria conflict with each other and tradeoffs must be made. To make tradeoffs between the two bidding criteria, a new bid markup selection making model is then developed by Cobb-Douglas utility function. The model generalizes the classical expected profit model in the sense that the latter's objective function is only a special case of the former. The result shows that the relative importance of a bidding criterion to another has significant effect on the selection of the equilibrium bid markup strategyThis work was supported partly by the National Natural Science Foundation of China
(No. 71001097 and 71171052) and China Postdoctoral Science Foundation (No.
201104167)S
Modeling peptide nucleic acid binding enthalpies using MM-GBSA
The binding enthalpies of peptide nucleic acid (PNA) homoduplexes were predicted using a molecular mechanics generalized Born surface area approach. Using the nucleic acid nearest-neighbor model, these were decomposed into sequence parameters which could replicate the enthalpies from thermal melting experiments with a mean error of 8.7%. These results present the first systematic computational investigation into the relationship between sequence and binding energy for PNA homoduplexes and identified a stabilizing helix initiation enthalpy not observed for nucleic acids with phosphoribose backbones
Enhanced bondline thickness analysis for non-rigid airframe structural assemblies
Adhesive bonding is a proven alternative to mechanical fasteners for structural assembly, offering lighter and thus more fuel efficient aircraft and cost-effective manufacturing processes. The effective application of bonded structural assemblies is however limited by the tight fit-up requirement, which is with sub-mm tolerance and can be a challenge for the industry to meet considering the variability of current part manufacturing methods and the conservative nature of the conventional tolerance stack-up analysis method. Such a challenge can discourage effective exploitation of bonding technologies, or lead to development of overengineered solutions for assurance. This paper addresses this challenge by presenting an enhanced bondline thickness variation analysis accounting for part deflection of a bonded skin-stringer assembly representing a typical non-rigid airframe structure. A semi-analytical model accounting for unilateral contact and simplified 1D adhesive flow has been developed to predict bondline thickness variation of the assembly under two typical curing conditions: namely autoclave curing and out-of-autoclave curing. The effects of component stiffness and manufacturing variations on bondline thickness are investigated by incorporating stringers of different stiffness, as well as shims of different thicknesses in-between the skin and stringer, in the stringer-skin assembly. A small-scale bonding demonstrator has been built and the physical results are in good agreement with the model prediction. It has been demonstrated that the part deflections need to be accounted for regarding fit-up requirement of bonded non-rigid structural assembly. The semi-analytical model offers more reliable and realistic prediction of bondline thickness when compared to a rigid tolerance stack-up. The analysis method presented can be a major technology enabler for faster, more economical development of the aircraft of the future, as well as of any analogue structures with high aspect ratios where weight savings and fatigue performance may be key objectives
Soluciones propias en la teorÃa de la dominación
Se relacionan varios conceptos de "punto propiamente no dominado", introducidos para eliminar soluciones no dominadas "poco deseables", dándose condiciones para las distintas implicaciones y equivalencia
Influence de l'addition de niobium sur les propriétés mécaniques des aciers à moyenne et haute teneurs en carbone
Soluciones no dominadas en problemas multiobjetivo
La TeorÃa de Estructuras de Dominación, introducida por P. L. Yu como nuevo procedimiento de solución a problemas multiobjetivo, presenta bastantes lagunas, debidas sin duda a la novedad del tema. Nos hemos propuesto en este trabajo caracterizar completamente los puntos no dominados, por distintos procedimientos, asà como seleccionar entre ellos un subconjunto más deseable ("soluciones propias"). Se abordan también condiciones para soluciones no dominadas en el espacio de decisione