Measurement and Prediction of Tape Cupping Under Mechanical and Hygrothermal Loads and Its Influence on Debris Generation in Linear Tape Drives

Abstract

Magnetic tapes, which may be modeled as three-ply laminates, exhibit transverse curvature, or cupping, as manufactured and when mechanical and hygrothermal loads are applied. Among other things, this cupping affects debris generation since it influences the contact between the flawed tape edge and head, the point where much of the debris generation occurs. This influence on debris generation is demonstrated experimentally in this study. Much more debris accumulates near the tape edge-head contact than at other contact locations. No difference in debris generation was found for two tapes with slightly different residual cupping (which is controlled during manufacturing). The target residual cupping is usually negative, which means that the tape bows out towards the tape so that the edges are farther away from the head than the center of contact is, so as to reduce contact pressure with the tape edges. However, cupping generally changes upon application of a tension and generally reduces the importance of residual cupping, which accounts for the failure to find a difference in debris generation for tapes with slightly different residual cupping. A finite element method model that uses laminate shell elements and accounts for in-plane stress stiffening, thus making it suitable for thin laminate modeling, was created. This modeling demonstrates that application of tensile and normal (used to simulate head contact) loads leads to cupping movement in the positive direction, which indicates a more severe edge contact, for an increase in front coat Young’s modulus and/or an increase in front coat thickness. The same trends hold for an increase in back coat Young’s modulus and/or an increase in back coat thickness. Modeling also demonstrates that cupping moves in the positive direction for an increase in the substrate’s Young’s modulus in the transverse direction for MP and ME tapes. An analytical model demonstrates that increases in temperature and front coat thermal expansion coefficient leads to cupping movement in the negative direction. The same trends hold for changes in relative humidity.