Composite sandwich structures are susceptible to low velocity impact damage and thorough characterization of the loading and damage process during impact is important. The objective of this work is to study experimentally the low velocity impact behavior of sandwich panels consisting of woven carbon/epoxy facesheets and a PVC foam core. Instrumented panels were impacted with a drop mass setup and the load, strain, and deflection histories were recorded. Damage was characterized and quantified after the test. Results were compared with those of an equivalent static loading and showed that low velocity impact was generally quasi-static in nature except for localized damage. A straightforward peak impact load estimation method gave good agreement with experimental results. A contact force–indentation relationship was also investigated for the static loading case. Experimental results were compared with analytical and finite element model analysis to determine their effectiveness in predicting the indentation behavior of the sandwich panel.

Low velocity impact behavior of composite sandwich panels

Finite element modeling of impact, damage evolution and penetration of thick-section composites

Impact damage can degrade the flexural strength of composite sandwich structures by over 50% due to a loss of skin support inducing localized skin buckling. Various self-healing methodologies have been applied to laminated composites but the concept of delivering a healing agent from a remote reservoir to a region of damage via a vascular network offers the potential for a robust and replenishable system housed in the core of a sandwich structure. In this pilot study a vascular sandwich structure that appears as a conventional sandwich composite has been developed and tested. The network has been shown to have negligible influence on the innate static mechanical properties of the host panel. Infiltration of the vascular network with a pre-mixed epoxy resin system after impact damage demonstrated a complete recovery of flexural failure mode and load. Infiltration with the same resin system from separate unmixed networks, where self-healing is initiated autonomously via mixing within the damage, has also been shown to fully recover undamaged failure load when both networks are successfully breached.

https://iopscience.iop.org/article/10.1088/0964-1726/16/4/031/pdf

Self-healing composite sandwich structures

Self-healing sandwich panels: Restoration of compressive strength after impact

Assessing the residual mechanical properties of a sandwich structure is an important part of any impact study and determines how the structure can withstand post impact loading. The damage tolerance of a composite sandwich structure composed of woven carbon/epoxy facesheets and a PVC foam core was investigated. Sandwich panels were impacted with a falling mass from increasing heights until damage was induced. Impact damage consisted of delamination and permanent indentation in the impacted facesheets. The Compression After Impact (CAI) strength of sandwich columns sectioned from these panels was then compared with the strength of an undamaged column. Although not visually apparent, the facesheet delamination damage was found to be quite detrimental to the load bearing capacity of the sandwich panel, underscoring the need for reliable damage detection techniques for composite sandwich structures.

Impact and post impact behavior of composite sandwich panels

A facility for testing of ballistic impact has been designed and developed. The goal was to develop a facility which was relatively easy to use and modify, as the requirements for the testing equipment changed with different research projects, e.g. students projects [1]. The setup consisted of a compressed air gun with an exchangeable barrel, a speed trap for measuring the incident velocity and a kinetic pendulum which both served as a means to measure the residual energy of the projectile and to catch the projectile from further travel. The aim of this paper was to cover some of the experiences encountered during the design and development high velocity impact test equipment.

Ballistic Impact Facility - Considerations and Experiences

Obemannade farkoster anvands allt oftare, och i allt fler roller, i dagens kon- flikter. Denna rapport ger en bred overblick over omradet militara obemannade farkoster, samt rekommendationer f ...

/pdf/forstudie-obemannade-farkoster-476wsebv34.pdf

Förstudie obemannade farkoster

Five technology forecast reports from the Fraunhofer Institute have been reviewed by staff at the Department of Military-Technology at the Swedish Defence University. The task given by the Swedish ...

Technology Forecast 2015, Military Utility of Five Technologies : a report from seminars at the Department of Military-Technology at the Swedish Defence University

The paper describes impact/bending testing of sandwich panels with 10 mm foam core and FRP face-sheets, with emphasis on test procedures, registration of results and description of the specialized test equipment developed. The sandwich panels were subjected to a cylindrical bending load of varying magnitude, while impacted at approximately 500 m/s. The impactor body was a steel sphere, diameter 10mm, with a mass of approximately 4g. The energy absorption and damage morphology of preloaded panels were compared with similar data for impact on specimens without preload. A high-speed camera was used for qualitative registration of panel response.

Concurrent Bending and Localized Impact on Sandwich Panels

A numerical model for ballistic impact of GFRP laminated panels has been presented where the panels may consist of one or multiple laminates. For the multiple laminated panel, identical laminates were placed parallel to each other with some gap in between and the impactor velocity was sufficient to penetrate all the laminates. The commercially available code ABAQUS 6.6 (explicit) has been used in the present study where the impactor has been modelled as a rigid body and the laminates have been modelled with a simple shell element. A material model based on a continuum damage mechanics concept for failure mechanism of laminated composites has been implemented through a user subroutine. The numerical model is found to predict the energy absorption reasonably well when compared with the experimental results. Most interestingly, it has clearly demonstrated a feasible phenomenon behind counterintuitive experiment results for the multiple laminated panels.

Peter H. Bull

Papers

Ballistic Impact Facility - Considerations and Experiences

Förstudie obemannade farkoster

Technology Forecast 2015, Military Utility of Five Technologies : a report from seminars at the Department of Military-Technology at the Swedish Defence University

Concurrent Bending and Localized Impact on Sandwich Panels

A simple shell model for simulation of localized impact on GFRP laminates