Analysis and interpretation of a test for characterizing the response of sandwich panels to water blast

Z. Wei, K.P. Dharmasena, H.N.G. Wadley, A.G. Evans
2007 International Journal of Impact Engineering  
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more » ... torate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law. no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. Naval ships. This research program sought to devise blast and ballistic protection concepts applicable to the design and fabrication of ship hull structures using AL6XN stainless steel sandwich panel constructions, which met threat and protection levels defined by the Navy. Efforts were undertaken in two phases to design, fabricate, experimentally investigate and analyze the quasi-static and dynamic behavior of sandwich beams and plates for several sandwich core topologies, at different size scales to evaluate their performance in underwater explosion (UNDEX), in air (AIREX), surface (SURFEX) and ballistic test environments. Several periodic cellular sandwich cores were assessed by performing dynamic uni-axial compression tests, stretch-bend type sub-scale (1/12 th and l/5 th full-scale) panel tests, and fullscale ballistic tests. Constitutive models were developed for the down selected core topologies to enable the implementation of more convenient large (ship) scale analyses. Soft response cores such as the prismatic cores and multilayer pyramidal cores were found better suited for water blast loading applications and ship hull blister attachments. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: a. REPORT Unclassified b. ABSTRACT Unclassified c. THIS PAGE Unclassified 17. LIMITATION OF ABSTRACT UL 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON H.N.G. Wadley 19b. TELEPHONE NUMBER (include area code) (434)982-5671 Standard Form 298 (Rev. 8-98) 20081031020 EXECUTIVE SUMMARY This research program sought to devise blast and ballistic protection concepts applicable to the design and fabrication of ship hull structures using AL6XN stainless steel sandwich panel constructions, which met threat and protection levels defined by the Navy. Efforts were undertaken in two phases to design, fabricate, experimentally investigate and analyze the quasi-static and dynamic behavior of sandwich beams and plates for several sandwich core topologies, at different size scales to evaluate their performance in underwater explosion (UNDEX), in air (AIREX), surface (SURFEX) and ballistic test environments. Several periodic cellular sandwich cores were assessed by performing dynamic uni-axial compression tests, stretch-bend type sub-scale (1/12 th and l/5 lh scale) panel tests, and full-scale ballistic tests. Constitutive models were developed for the down selected core topologies to enable the implementation of more convenient large (ship) scale analyses. Soft response cores such as the prismatic cores and multilayer pyramidal cores were found better suited for water blast loading applications and ship hull blister attachments. Technical Approach The approach used in this research program exploited progress made in metallic sandwich panel design and optimization concepts and advances made in fabrication techniques. Guidance from collaborating groups performing modeling work (ATR, Burtonsville, MD, Naval Surface Warfare Center, Indian Head, MD and University of California, Santa Barbara) was used to select sandwich panel design parameters for face sheet, core thicknesses, the relative density of the core, and panel sizes for quasi-static and dynamic load testing. Panels were fabricated using a transient liquid phase bonding approach while an alternate joining technique such as laser welding was explored for scaled-up panel fabrication. The ballistic protection capability of selected sandwich panels were investigated either by integrating a hard ceramic within the sandwich core or as a backing placed against the sandwich panel. Underwater explosion (UNDEX) tests were performed on several candidate sandwich panel designs at the Naval Surface Warfare Center in Carderock, MD. A breakdown of key research performed during the two phases is given below and a list of more detailed papers resulting from the overall research effort is given at the end of the report (Appendices A-G). Achievements (Phase I) Periodic cellular material cores can be broadly categorized in to three classes, (a) prismatic, (b) honeycomb, and (c) microtruss cores. The core deformation, strength, and energy absorption of each of these classes is a function of the sandwich panel design geometry, the material properties, and specific loading condition, (e.g. compression, shear, bending). The core deformation, strength, and energy absorption of each of these topology classes is a function of the sandwich panel design geometry, the material properties, and specific loading condition, (e.g. compression, shear, bending). During Phase I, sandwich panels with periodic cellular cores covering all three topology classes were fabricated for dynamic compression tests ("Dynocrusher" test) in a modified paddlewheel test device used by the Naval Surface Warfare Center, Carderock, MD for underwater explosion (UNDEX) tests. For the dynocrusher tests, 8-inch diameter, 4-inch thick cylindrical shaped, 304 and AL6XN grade stainless steel alloy samples were designed, fabricated by the University of Virginia and tested at NSWC Carderock in the regular corrugation, diamond corrugation, square honeycomb, triangular honeycomb, and pyramidal core topologies. Four out of the five topologies are shown in Figure 1 . 23 pyramidal core layers (each -1.0 in.) 22 intermediate sheets (each 0 030 in) Core relative density-O.OS 14GAI6XN sheet. perlorated and formed shape j, U-0.10 in Projectile 24 in tall -i 0.5 in. ABXN outer lace plate 24 in. panel width 0.25 in. AL-6XN plate (for txare sandwich panel test) 0.1875 in. AL-6XN plate (lor panel tested with armor pack) 12 A dynamic version of the constitutive law was developed (Appendix I). It was calibrated by using dynamic unit cell simulations. The input embodies the material strain rate sensitivity as well as the inertial effect associated with buckling suppression. Comparisons with dynamic experimental measurements were performed involving impact by a metal foam projectile onto a square honeycomb panel at high impulse at strain rates of order 1,000/s and the "dynocrusher" test simulation on the multilayer pyramidal core panel and multilayer prismatic (triangular core and diamond core) panels. The experimental and analysis efforts of this program indicated that a soft core response was preferred for water blast loading, since the soft cores such as the X-truss core and multi-layer pyramidal core enabled the dissipation of the impulse over a longer time period at lower transmitted peak, pressures than stronger cores such as the square and triangular honeycomb cores. Further consideration was also given to the ease of fabrication of larger (12" and 24" thick cores, i.e. half-scale and full-scale) with these topologies in the form of blisters conforming to the curved profiles of the proposed ship hulls, and a final recommendation was made to select a X-truss core topology. Abstract The quasi-static and dynamic compressive mechanical response of a multilayered pyramidal lattice structure constructed from stainless-steel was investigated. The lattices were fabricated by folding perforated 304 stainless steel sheets and bonding them to thin intervening sheets using a transient liquid-phase bonding technique. The resulting structure was attached to thick face sheets and the through thickness mechanical response was investigated quasi-statically and dynamically, in the latter case using a planar explosive loading technique. The lattice is found to crush in a progressive manner by the sequential (cooperative) buckling of truss layers. This results in a quasi-static stress strain response that exhibits a significant "metal foam" like stress plateau to strains of about 60% before rapid hardening due to truss impingement with the intermediate face sheets. During dynamic loading, sequential buckling of the truss layers was manifested as a series of transmitted pressure pulses measured at the back face of the test samples. The sequential buckling extended the duration of the back face pressure-time waveform and significantly reduced the transmitted pressure measured at the back face. The impulse transmitted to the structure is found to be about 28% less than that predicted by analytic treatments of the fluidstructure interaction for fully supported structures. This transmitted impulse reduction appears to be a consequence of the wet side face sheet movement away from the blast wave and is facilitated by the low crush resistance of the lattice structure. Abstract Metallic sandwich panels are more effective at resisting underwater blast than monolithic plates at equivalent mass/area. The present assessment of this benefit is based on a recent experimental study of the water blast loading of a sandwich panel with a multilayered core, using a Dyno-crusher test. The tests affirm that the transmitted pressure and impulse are significantly reduced when a solid cylinder is replaced by the sandwich panel. In order to fully understand the observations and measurements, a dynamic finite element analysis of the experiment has been conducted. The simulations reveal that the apparatus has strong influence on the measurements. Analytic representations of the test have been developed, based on a modified-Taylor fluid/structure interaction model. Good agreement with the finite element results and the measurements indicates that the analytic model has acceptable fidelity, enabling it to be used to understand trends in the response of multilayer cores to water blast. Sandwich panel structures with thin front faces and low relative density cores offer significant impulse mitigation possibilities provided panel fracture is avoided. Here steel square honeycomb and pyramidal truss core sandwich panels with core relative densities of 4% were made from a ductile stainless steel and tested under impulsive loads simulating underwater blasts. Fluid-structure interaction experiments were performed to (i) demonstrate the benefits of sandwich structures with respect to solid plates of equal weight per unit area, (ii) identify failure modes of such structures, and (iii) assess the accuracy of finite element models for simulating the dynamic structural response. Both sandwich structures showed a 30% reduction in the maximum panel deflection compared with a monolithic plate of identical mass per unit area. The failure modes consisted of core crushing, core node imprinting/punch through/tearing and stretching of the front face sheet for the pyramidal truss core panels. Finite element analyses, based on an orthotropic homogenized constitutive model, predict the overall structural response and in particular the maximum panel displacement. Abstract The responses of metallic plates and sandwich panels to localized impulse are examined by using a dynamic plate test protocol supported by simulations. The fidelity of the simulation approach is assessed by comparing predictions of the deformations of a strong-honeycomb-core panel with measurements. The response is interpreted by comparing and contrasting the deformations with those experienced by the same sandwich panel (and an equivalent solid plate) subjected to a planar impulse. Comparisons based on the center point displacement reveal the following paradox. The honeycomb panel is superior to a solid plate when subjected to a planar impulse, but inferior when localized. The insights gained from an interpretation of these results are used to demonstrate that a new design with a doubly-corrugated soft core outperforms solid plates both for planar and localized impulses. Published by Elsevier Ltd. Abstract The dynamic crush response of a low relative density, multilayered corrugated core is investigated by combining insights from experiments and 3D finite element simulations. The test structures have been fabricated from 304 stainless steel corrugations with 0°/90° lay-up orientation and bonded by means of a transient liquid phase method. Characterization of the dynamic crushing of these structures has revealed that at low rates, interlayer interactions induce a buckling-dominated soft response. This softness is diminished at high rates by inertial stabilization and the response of the structure transitions to yield-dominated behavior. Unidirectional dynamic crushing experiments conducted using a dynamic test facility reveal a soft response, consistent with lower rate crushing mechanisms. The 3D simulation predictions of crushing strain, pulse amplitude/duration and impulse delivery rate correspond closely with the measurements. The application of core homogenization schemes has revealed that by calibrating with a multilayer unit cell, high fidelity continuum level predictions are possible. Moreover, even simplified hardening curves based on equivalent energy absorption provide remarkably accurate predictions of the crush strains and the impulse transmitted through the core. The multilayered structures investigated here significantly reduced the transmitted pressures of an impulsive load. Abstract The compressive response of rigidly supported stainless steel sandwich panels subject to a planar impulsive load in water is investigated. Five core topologies that spanned a wide range of crush strengths and strain-dependencies were investigated. They included a (i) square honeycomb, (ii) triangular honeycomb, (iii) multi-layer pyramidal truss, (iv) triangular corrugation and (v) diamond corrugation, all with a core relative density of approximately 5%. Quasi-statically, the honeycombs had the highest peak strength, but exhibited strong softening beyond the peak strength. The truss and corrugated cores had significantly lower strength, but a post yield plateau that extended to beyond a plastic strain of 60% similar to metal foams. Dynamically, the transmitted pressures scale with the quasi-static strength. The final transmitted momentum increased slowly with core strength (provided the cores were not fully crushed). It is shown that the essential aspects of the dynamic response, such as the transmitted momentum and'the degree of core compression, are captured with surprising fidelity by modeling the cores as equivalent metal foams having plateau strengths represented by the quasi-static peak strength. The implication is that, despite considerable differences in core topology and dynamic deformation modes, a simple foam-like model replicates the dynamic response of rigidly-supported sandwich panels subject to planar impulsive loads. It remains to ascertain whether such foam-like models capture more nuanced aspects of sandwich panel behavior when locally loaded in edge clamped configurations.
doi:10.1016/j.ijimpeng.2006.09.091 fatcat:x4szcubfdza73drs2gw4yffkfu