Etude par diffraction des neutrons de la repartition des contraintes autour de l'interface metal-adhesif

The technique of neutron diffraction is often used to evaluate internal stresses in bulk materials. We used this technique to measure the stresses near a metal adhesive interface. The assemblage, in the form of two bevelled half test bar aluminium alloy, is assembled by a single component epoxy adhesive. The quality of the bonded joint is controlled by neutron radiography. For the (111) diffraction plane of the aluminium alloy, the modulus of elasticity E and Poisson's coefficient are 73110 MPa and 0.32, respectively. For the adhesive E = 5400 MPa and v = 0.33. We used a wavelength of 3.29 A and the analyzed volume by the neutron beam is 1.5 × 2 × 13 mm³. The sample was loaded by 11 kN in its longitudinal direction, using a strain rig specially designed so that it can be accommodated on the sample test of the neutron diffraction. We used the 1D experimental method to carry out a map of the isodeformations and the 3D method to study the influence of a macroscopic defect in the adhesive joint on the stress field. The map of isodeformations obtained before and after loading shows that an important residual stress field exists in the adhesive assemblage. These residual stresses may come from the chemical reactions of polimerization or to the sharp fluctuations temperature during the assembling process. On the other hand, the map obtained with the finite element analysis is markedly different. This means that an important residual stress field and defects are presents in the adhesive joint. With the 3D method, the measurement was restricted to a particularly interesting region of the sample. The principal stresses obtained by neutron diffraction are: σxx = 34 MPa, σyy = 3 MPa, σzz = 23 MPa and with finite element analysis: σxx = 52 MPa, σyy = 0 MPa, σzz = 0 MPa. In this case the results obtained by the two different techniques are quite similar.