Unbonded Layer Research Articles

Interfacial instabilities in an unbonded layered solid

A bifurcation problem relevant to the process of roll-bonding is studied. The simultaneous rolling of several unbonded layers is modeled as a plane strain compression of the unbonded layers. To gain insight into the phenomenon of tiger banding, the strains at which there can exist bifurcation modes which involve an undulating interface between the layers are computed. Particular attention is focused upon the effect of permitting slip between the layers, in contrast to the assumption of velocity continuity that underlies previous analyses of bifurcation in layered solids. Velocity discontinuity implies that the bifurcation condition depends on the hydrostatic pressure; the consequences of this dependence are highlighted.

突合せ接着継手の疲労挙動に関する研究 未接着部の影響について

As a part of our ongoing study to investigate the effect of adhesive defects on fatigue strength of adhesive-bonded joint, a series of fatigue tests were carried out by using adhesive-bonded butt joints with unbonded layer at adhesive/adherend interface under the push-pull fatigue load condition of stress ratio R=-1.0.The specimens used possessed two unbonded portions of nail shape along the adhesive/adherend interface, which were located at the opposite sides of the specimen. To characterize the defect size quantitatively, it was defined by the following two quantities; the unbonded width which was the same as the defect length exposed to the free surface of the specimen, 2r, and the unbonded depth from the free surface, l.The fatigue strength of the adhesive-bonded joint specimens with two kinds of unbonded width (2r=3, 5mm) was discussed in connection with the unbonded depth l. The main results obtained in this study are as follows:(1) For the specimen with 2r=3mm, the fatigue strength decreased with increasing l in the low stress cycle range. But, the effect of l on the fatigue strength diminished with increasing stress cycles.(2) For the specimen with 2r=5mm, the fatigue strength decreased with increasing l irrespective of the number of stress cycles.

Non-destructive interferometric detection of unbonded layers

Non-destructively detecting and monitoring delaminated areas in stratified materials is an important industrial problem. The possibility of characterizing such delaminations by interferometric dilatometry is analyzed in this paper. A Cu-Be strip adhesively bonded to a massive substrate is resistively heated and its thermal expansion is monitored by a laser interferometer. Large signals are obtained from the unbonded regions, as expected from the theoretical calculations. The initial curvature of the unbonded layer is shown to have a major effect on the lifting capability of uniformly heated layers.

Buckling of stiffened two-layered shells of revolution with a circumferentially cracked unbonded layer.

Orthotropic stiffness layer models are derived for buckling of eccentrically stiffened shells of revolution with two unbonded orthotropic layers: 1) both of which are uncracked, and 2) one of which is circumferentially cracked. The two models are used in conjunction with a theory for buckling of eccentrically stiffened, circular cylindrical shells with multiple orthotropic layers to assess the importance of including the ablative layer in design calculations for two-layered (metallic plus ablative) re-entry vehicle shells. It is demonstrated in the present analysis that the ablative layer, even when circumferentially cracked and not bonded to the metallic layer, actually dominates the buckling stiffness of a re-entry vehicle shell and, hence, provides an already available source of stiffness for design calculations. However, the current treatment of the ablative layer is to either ignore it completely (an unduly conservative approach) or to regard it as uncracked and perfectly bonded to the metallic layer (an unconservative approach).