The problem of transverse impact on large orthotropic elastic plates due to moving impactors is investigated in this paper. The contact force produced during impact is obtained through Sveklo's contact theory for anisotropic bodies. The usual assumption of the contact force being concentrated at a point has been discarded, and instead the elliptical contact region as predicted by the contact theory is considered. The contact force history and the central deflection are only marginally influenced by this replacement as long as the size of the ellipse does not exceed a limit, which for a graphite fiber/epoxy plate of thickness 8 mm is about 1 X 10 ~4 m; i.e., the size of the ellipse is approximately 1/80 of the plate thickness. However, there is a noticeable effect of a nonzero contact area on the evaluation of the bending curvatures. Also, the well-known singularity in this evaluation is eliminated. The analysis has been illustrated for the case of a graphite fiber-reinforced epoxy plate impacted by steel balls. I. Introduction W ITH the increasing use of fiber-reinfor ced composite materials as load bearing structural members, it is essential to understand their response to transverse impact loads for two reasons. Firstly, it is well known that the impact resistance of these materials is poor although the static strength and stiffness in the fiber direction are very good. Secondly, even under low-velocity impact loading, these materials can suffer damage such as internal cracking or delamination. Aircraft structural components where these materials are often used are some times subjected to foreign body impacts such as bird strikes, inadvertent falling of tools during maintenance, etc. These accidental loadings can be very serious and the damage is often invisible. Therefore, a detailed understanding of the dynamic behavior of plates and beams made of aligned fiber-reinforced composites when struck by a moving object is very much needed. For isotropic materials this problem has received adequate attention and the results are well-documented.1'3 As will be discussed in the next section, this problem is a synthesis of two important problems in the mechanics of solids, viz. the interaction between two bodies in contact and pressing against each other (contact law) and the response of a beam or plate to a known force history. Often this force is assumed to be concentrated at a point. For two isotropic bodies in contact, Hertz's contact law is generally used. However, when one of the bodies involved in contact is orthotropic as in the case of a compact isotropic body (impactor) striking a fiber-reinforced plate, then Hertz's law needs to be modified or replaced by a law which is also applicable to anisotropic bodies. Various modifications of Hertz's law for transversely isotropic bodies and generally orthotropic bodies have been discussed by Greszczuk.4 One of the simplest modifications is to replace the expression E/( - v 2) occurring in the case of an isotropic plate by Ez/( - v zrvrz) for a transversely isotropic plate where Ez is the elastic modulus in the thickness direction (z-axis) and the u's are the two Poisson's ratios in the r-z plane. This simple modification has been used by some authors5'6 for an orthotropic plate arguing that vzrvrz — 0, while many investigators have preferred to use a contact law determined from static indentation tests.7'10 It