Composite materials are substance consisting of two or more materials, insoluble in one another, which are combined to form a useful engineering material possessing certain properties than those of the individual components used alone. Because of the high strength to weight ratio and damage tolerance composite materials, especially carbon fiber reinforced polymer (CFRP) shell structures are finding many applications in aerospace applications . The loads which can occur during its service life must be taken into account for a stable and reliable structural design. Low-velocity impacts are considered potentially dangerous for a composite shell structures, even subjected to a low velocity Impact, these shell structures may sacrifice its load carrying capacity due to various modes of failure . Several areas have been accounted which are not fully exploited and restrict potential advancement of weight-efficiency of composite structures namely, post-buckling capabilities, imperfection robustness and loading dynamics. Many works concerned with the buckling response of thin cylindrical shells have been published and the different modes of failure [3–7], have been described. In this work low velocity impact response of composite cylindrical shell structures have been analyzed by means of experimental testing and numerical simulations
Vasiliev et al investigated the history of the lattice structures  development and made the founding studies on fabrication techniques. They proposed that the modern unidirectional carbon composites, being loaded along the fibers, are characterized with specific strength and stiffness than the corresponding characteristics of aluminum alloys. The anisogrid composite lattice structures are thin walled cylindrical shells ,  composed of both helical and circumferential ribs articulated in such a way that confined defects in the grid do not grossly affect the universal behavior of the structure. Buragohain et al carried out a study of filament wound ,  grid-stiffened composite cylindrical structures. The composite lattice structures have been considered as the excellent replacement for conventional solid and honeycomb structures.
Morozov et al have reported that Anisogrid composite shells  are used in various structural applications, such as rocket interstages, payload adapters for spacecraft launchers, fuselage components for aerial vehicles, and components of the deployable space antennas. Recently, Buragohain et.al reported the optimal design of filament wound grid-stiffened composite cylindrical structures. According to them the grid of stiffening ribs that are made by filament winding makes such a structure very highly efficient and reliable. Zhifeng Zhang et.al demonstrated a progressive failure  methodology to simulate the initiation and propagation of multi failure modes for advanced grid stiffened (AGS) composite plates/shells on the basis of a stiffened element model.
Polymer matrix composite laminates are prone to delamination when impacted, resulting in low damage tolerances, which is of great concern for load carrying applications. The impact behavior of composite materials has been investigated by many authors , . Damages in composites are different from those in metals. Composite failure is a progressive accumulation of damage, including multiple damage modes and complex failure mechanisms , . Our earlier investigations  proved that the anisogrid shell structure deliver more energy absorption than the unstiffened shell structure under static loading condition. Recently, the effects of impact energy levels, impact locations and changes in layer thickness of 3D printed thermoplastic plates were studied . In addition to the available literature on anisogrid shell structures over the past decades, this paper present another more recent approach to the experimentation and numerical simulation of CFRP shell structures. The objective of this study is to compare the impact response of the CFRP shells plain cylinder and anisogrid, when they are dynamically loaded in axial direction. The developed numerical models were validated with the obtained experimental results. The present paper deals with the following phases of work:
- Infrared thermography Nondestructive testing (IRNDT) of the CFRP test coupons followed by material characterization as per ASTM standards for the estimation of unidirectional elastic and strength properties.
- Fabrication of CFRP cylindrical shell structures viz., unstiffened (plain cylinder) and anisogrid using newly developed filament winding machine.
- Experimental and Finite element analysis (FEA) of unstiffened and anisogrid CFRP cylindrical shell structures under axial impact.