Stability and mechanics of precision deployable structures under nanometer deformation

This thesis presents a phenomenological investigation of the geometric stability of precision deployable structures at nanometer levels of deformation. Previous concern of the effect of microslip in the joints of large deployed spacecraft structures has limited their consideration for optical applications. The results of this thesis show that, for loads at 1–5% of the Coulombic yield level and for low load rates, structural mechanics produce the type of responses predicted by recent theories. However, results also indicate that spontaneous transient responses, not predicted by these theories, can occur. These imply together that highly jointed spacecraft structures might be kept sufficiently stable for optical applications under low loads, if the effects of frictional microslip are considered.; The expected behavior of jointed structures is extrapolated from prior observations of microslip friction mechanics. A phenomenological model is used to develop a load scale factor called the Coulombic Friction Yield Ratio. This is the ratio of the actual applied load to the applied load required to cause full slip in the interface.; A unique experimental facility, that separates environmental effects from the desired mechanics at nanometers of deformation enabling 1000 times better resolution, thermal stability and bandwidth than previous experimentation, is developed.; The mechanics of a composite material specimen are first considered to determine whether material anelasticity should be suspected in the mechanical instability at nanostrain. Following this, the primary emphasis is on the investigation of mechanical manifestations of a jointed structure.; The results support the following conclusions regarding jointed, deployable structures. First, permanent hysteresis and harmonic distortion persist at nanometers of deformation, as theory predicts, but generally can be reduced with lower load ratios. Second, a viscoelastic effect is observed, at nanometer deformation levels, that is suspected to be due to yield mechanics in the frictional interfaces. Finally, load levels that are less than 10% of the Coulombic Friction Yield Ratio produce rare, spontaneous dynamic responses that appear to be the release of stored mechanical energy during load cycling. These dynamic responses suggest the need to revise microslip mechanics to include dynamic instabilities if they are due to slippage in the joint.