Alain Daidié

Optimization of a high-pressure pore water extraction device

High-pressure squeezing is a technique used for the extraction of the pore water of porous materials such as sediments, soils, rocks, and concrete. The efficiency of extraction depends on the maximum pressures on the materials. This article presents the design of a high-pressure device reaching an axial pressure of 1000 MPa which has been developed to improve the efficiency of extraction. The increase in squeezing pressure implies high stresses inside the chamber, so specialized expertise was required to design a safe, functional device that could withstand pressures significantly higher than common laboratory equipment. The design includes finite element calculations, selection of appropriate materials, and descriptive construction details for the apparatus. It also includes an experimental study of the performance of the apparatus in terms of extraction efficiency.

Stiffness and slip laws for threaded fasteners subjected to a transversal load

This article focuses on improving the design methods for simplified models of screwed connections (spring, beam or bar elements), especially for the space sector. A detailed 3D model of a generic screwed connection has been developed using industrial finite elements (FE) software. An approach based on multiscale numerical designs of experiments (DOE) was used to obtain metamodels of stiffness and slip depending on geometric, material and contact parameters. In order to improve the integration of friction, an existing contact model was adapted and used to supply a modified Coulomb model. Metamodels from these numerical works were compared and correlated with experimental double shear tests on a specimen loaded by an imposed transverse displacement.

Numerical modelling of the cold expansion process in mechanical stacked assemblies

The cold expansion process is a technology that is widely used to enhance the fatigue resistance of aircraft metallic parts. The issue analysed in this paper concerns the case when the expansion is carried out through an assembly composed of several sheets. The numerical work conducted was intended to understand the phenomenology of the process within a stiff assembly. In particular, it aimed to analyse the deformation of the sheets and the residual stress fields generated by the process. For this purpose, an axisymmetric finite element model of the split sleeve process was developed, simulating a single expansion performed through a stack of two titanium holes (Ti-6Al-4V). The sheets to be expanded were positioned between two steel plates to simulate the assembly. The model could predict the shape and intensities of the fields within the expanded sections and their global outer shapes. We particularly focused on the phenomena prevailing between sheets. The simulation showed that deformations at the interface were greatly reduced when the stack was stiffened axially. Moreover, high circumferential and axial residual stresses were generated in the sheets. Results were compared with a single hole expanded without axial stiffening.

Experimental Study of Bolted Joint Self-Loosening Under Transverse Load

Self-loosening of bolted joints is a problem regularly encountered in aeronautical structures and much research has been devoted to this phenomenon. Developing detailed analytical equations for the dynamic study of unscrewing is difficult, so it is easier to reveal it experimentally, in the static or the dynamic case. This paper focuses on the experimental study of the dynamic self-loosening of a bolted joint when it is subjected to vibrations, a major cause of the problem. The experiment used a bolted assembly moved by a shaker, which caused the tightened parts to slide and the bolt to loosen. A load washer showed the axial load variation and a high speed camera recorded the movements of the assembled parts. The results show the progress of rotation of the different parts, the unscrewing of the bolt and the loss of tension in the assembly. The method provides a means to explore the loosening process of various types of bolts, under realistic conditions of vibration.

Behavior of Single-Lap Bolted Joint Subjected to Dynamic Transverse Load

Bolted joints used in aeronautical structures are subject to vibrations, which can result in critical damage either from self-loosening or from fatigue. This study is devoted to the examination of the dynamic behavior of a simple bolted joint assembly subjected to quickly varying transverse load, which induces bending of the jointed plates. The adopted approach is based on finite element method, with a coupled bolt model and a penalty friction model, and implicit time simulation. Numerical result sets are presented and discussed.

EFFECT OF AXIAL PRELOAD ON DOUBLE-LAP BOLTED JOINTS - NUMERICAL STUDY

This paper presents the numerical study of double-lap bolted joint behavior. This type of joint is mainly used in aeronautical structures to transfer the given loads (by both adhesion and by deformation-shearing). Recent articles, based on experimental fatigue tests conducted by AIRBUS, have shown the beneficial effects of preloading on the fatigue life of these joints.Finite element analyses were performed using ABAQUS® to study the behavior of a double-lap single-bolted joint with different plate thicknesses (joint thickness = 0.5d, 1d, 1.5d, 2d 2.5d, 3d, 3.5d and 4d, where d is the bolt diameter).The numerical model provides several important results. In the case of static loads, elasto-plastic constitutive laws of the bolt and the plate materials allowed the process to be simulated on the basis of tension tests.Mechanical aspects of this type of assembly are numerically identified; from the initial state of adhesion to the state of plastic deformation of parts in contact including the stage of generalized slippage. We note that the fracture load increases slightly when the bolted joint is preloaded while the failure area remains the same. In the case of large plate thickness, the connection is subjected to significant bending stresses and this involves strong local plasticization associated with the loss of preload.In the case of cyclic loading, we consider a numerical model based on the simulation of one loading/unloading cycle. A noticeable decrease in initial preload is observed for certain configurations, in particular those with the largest plate thickness. This phenomenon is related to the effect of strain hardening of the bolt during the first loading cycles. Some experimental work by AIRBUS has shown that the fatigue life of assemblies is dependent on the material plate thicknesses.An extension to the case of a multiple-bolted joint (three rows of three bolts) is finally discussed and highlights the evolution of the rate of load transmission with respect to the applied load.Copyright