B. SANDWICH STRUCTURES On the Performance of Micro Lattice Structures as Core Materials in Sandwich Panels Subject to Low Velocity Impact R Mines, S Tsopanos, E Shen, S McKown, W Cantwell (Univ of Liverpool) Small sandwich panels, with dimensions of 100mm by 100mm by 20mm, have been manufactured with stainless steel micro lattice cores produced by selective laser melting and with carbon epoxy skins. These panels have been subjected to drop weight loading from a steel hemisphere, and resultant damage has been quantified. (B6:1) Developments of Novel Composite Cellular Materials based on the Auxetic Concept G Recca, G Cicala (Univ of Catania) F Cicala, A Lorato (Univ of Bristol) The present paper is focused on some novel auxetic composite materials based on a novel RTM production process invented and patented by the some of the authors. The novel materials can well withstand loads and, as such, have a structural function. In the paper the comparison with traditional cores and the effect on the mechanical properties of several types of fibers and resins will be presented. (B6:2) Novel Tri-Coordinated Chiral Honeycombs A Alderson, K Alderson, N Ravirala, K Zied (Univ of Bolton) A combined experimental and modelling study has been carried out on a family of tricoordinated chiral honeycombs. The honeycombs have been characterised for in-plane and out-of-plane mechanical properties. Careful selection of the honeycomb geometry enables both positive and negative in-plane Poisson’s ratios, including one example of negative inplane but positive out-of-plane bending response. (B6:3) Tailored Stiffness of Balsa Sandwich Core Material J Kepler (Aalborg Univ) A concept for tailoring the stiffness properties of balsa core material to sandwich structures is presented. The concept is modeled using basic laminate theory to predict the transverse/lengthwise properties with respect to a sandwich beam. This is subsequently validated through experiments. A substantial improvement on the shear stiffness is demonstrated. (B6:4) Modelling Of The Behaviour Of Aramid Folded Cores Up To Global Crushing E Baranger, C Cluzel, P-A Guidault, O Allix (LMT-Cachan) This paper presents the basic ingredients needed to model the compaction behaviour of an aramid paper folded core up to the global collapse load under crushing. The proposed approach is both experimental and numerical. Different scales are taken into account: fibre, paper and core scales. This multiscale approach is illustrated. (B6:5) Shape Memory Sandwich Panels D Radford, A Antonio (Colorado State Univ) Thermosetting resins and foams have recently been introduced which show elastic shape memory properties. Preliminary efforts to develop sandwich panels based on shape memory resin and foam core are discussed. Results show that large deformations can be generated, retained in stiff sandwich panels, and recovered, as required. (B6:6) T Thomsen/P Cunningham WEDS 09.10 B. SANDWICH STRUCTURES oral Failure Mode Shifts in Fatigue of Sandwich Beams D Zenkert, M Burman (Kungliga Tekniska Högskolan) Failure mode shifts of a sandwich beam subjected to fatigue loading in four-point bending will be investigated experimentally. It is predicted that the beam will fail by core shear for high load levels (few number of cycles to failure) and by face tension failure for low levels (large number of cycles to failure). (B6:7) Experimental Investigation of Blast Resistance and Energy-Absorption Characteristics of Sandwich Composites with Stepwise Graded Cores A Shukla, E Wang, N Gardner (Univ of Rhode Island) NEEDS 50 WORD ABSTRACT (B6:8) Damage Zones and their Growth in Sandwich Composites under Hull Slamming Loading Conditions G Ravichandran, M Silva (California Institute of Technology) The evolution of failure mechanisms in sandwich structures under dynamic fatigue loading conditions is analyzed. Damage initiation threshold and growth is characterized as a function of loading duration, frequency and amplitude of pulses imparted on sandwich panels. Thermal imaging techniques reveal the presence of damage within the composite samples. (B6:9) Dynamic Behaviour of Sandwich Beam with Internal Resonators CT Sun, J-S Chen (Purdue Univ) A foam core sandwich beam with embedded internal resonators is studied for its dynamic behaviour. The sandwich beam is modelled as a Timoshenko beam with attached masses. For harmonic waves with wave frequencies near the resonance frequency of the internal resonators, the flexural motion is almost totally suppressed. (B6:10) Repeated Slamming of Foam Core Sandwich Composite Panels on Water B Shafiq, S Charca, F Just (Univ of Puerto Rico) Wave slamming was simulated by repeatedly slamming rectangular foam core sandwich composite specimens mounted on a rigid wedge onto the body of calm water. Experiments were conducted as a function of slamming energy level and deadrise angle in order to generate an E-N (slamming energy vs lifetime) curve. (B6:11) Global Buckling of Sandwich Beams/Wide Panels: An Elasticity Solution and Comparison with Sandwich Buckling Formulas G Kardomateas, G Simitses (Georgia Institute of Technology) NEEDS 50 WORD ABSTRACT (B6:12) 11.30 Novel Experimental Techniques to Determine Fracture Toughness of Cellular Foam and Sea Water Effects D Penumadu, J Weitsman, A Siriruk, K Thomas (Univ of Tennessee) A new experimental setup has been developed that can measure mode-1 fracture toughness of foam core material for sandwich composites with controlled crack growth that is channelled along the mid plane. Techniques to obtain mixed mode fracture behaviour by the application of combined tension and torsion on flat, pre-cracked foam specimens will be presented. (B6:13) Immersed and Dry Fatigue Behaviour of Carbon Fiber and Vinyl Ester Sandwich Facing Materials J Weitsman, D Penumadu, A Siriruk (Univ of Tennessee) Experimental results for carbon fiber reinforced vinyl ester composites that serve as facings for naval sandwich structures yielded failures under much fewer number of cycles when fatigued under immersed conditions. Failure mechanisms leading to this significant degradation in fatigue behaviour of composites under sea water confinement are discussed. (B6:14) A Vibration Technique to Obtain Fatigue F Just-Agosto, B Shafiq, D Serrano, A Perlata (Univ of Puerto Rico) A finite element based structural shape synthesis technique to design a vibration specimen for fatigue lifetime evaluation is developed. The procedure involves vibrating the specimen in resonance in order to produce a stress pattern in a given region that emulates a typical flexural fatigue test. A design shape optimization procedure is described and validated for a foam core material with flexural fatigue experimental results. (B6:15) Eco-Core and its Performance in Sandwich Structural Application K Shivakumar, H Chen (North Carolina A&T State Univ) Eco-Core is a fire resistant structural core material for composite sandwich structures. Structural performance of Eco-Core glass/vinyl ester sandwich beams was evaluated for transverse and edgewise loadings. Core shear, core tension and face sheet microbuckling were the failure modes and the associated equations for failure loads were developed and verified. (B6:16) 13.50 Sandwich Panels with Cellular Cores Made of Folded Composite Material: Mechanical Behaviour and Impact Performance S Heimbs, J Cichosz (EADS) Innovative sandwich core structures can be produced by folding composite prepreg sheets to three-dimensional zigzag structures. This paper describes the cell walls’ mechanical behaviour under flatwise compressive loads as well as low and high velocity impact loads. Experimental results and modelling issues for dynamic simulations are discussed. (B6:17) Non-Explosive Simulated Blast Loading of Composite Sandwich Beams H Kim, A Chen (Univ of California) A dynamic loading method for simulating explosive blast was developed using a crushing foam projectile launched by a gas gun at velocities ranging from 30-70 m/s. This test method is used to load composite specimens that allow for the dynamic failure characterization of carbon/epoxy sandwich structures. Such methods are desirable since they are easier and safer to implement than real explosive blast tests. (B6:18) Characterization and Analysis of Composites Sandwich Ramp Failure I Paris (Bombardier Aerospace) F Theriault (Bell Helicopter Textron Canada Ltd) M Hojjati, J Chen, A Yousefpour, M-A Octeau (National Research Council Canada) NEEDS 50 WORD ABSTRACT (B6:19) Residual Strength Simulations of Sandwich Panels after Impact H-G Reimerdes, M Klaus (RWTH Aachen) The impact behaviour of sandwich panels with different core structures and their residual strength after impact are investigated. The focus in this study is the development of a procedure which allows to simulate the impacts and to perform numerical residual strength simulations with the pre-damaged FE models. (B6:20) Material Property Steered Optimization of a Multifunctional Body Panel to Structural and Acoustic Constraints CJ Cameron, P Wennhage, P Göransson (Royal Institute of Technology (KTH)) A conventional automobile roof, including structural and interior trim components, is replaced with a multi-layer, multi-functional sandwich construction. A weight optimization is performed to tailor the material properties of the composite face sheets and multiple foam layers to meet structural constraints and sound transmission loss requirements. (B6:21) Solution of Time-Dependent Problems in Sandwich Beams and Plates Solved with RBF/Ps Method AFerreira (FEUP/DEMEGI) A study of various time-dependent problems for sandwich beams and plates is presented with the radial basis function/pseudospectral hybrid method. A method based on Rippa’s cross-validation technique is used to optimize the shape parameter for the radial basis functions. (B6:22) HG Reimerdes C Berggreen Thursday 09.10 Evaluation of Advanced Crack Arrester for Foam Core Sandwich Panel Mode I Type Loading Condition Y Hirose, H Matuda, G Matsubara (Kawasaki Heavy Industries) M Hojo (Kyoto Univ) The authors contrived an advanced type crack arrester using core-core splices. The analytical estimation and experimental validation of this concept, named the splice-type crack arrester, have been carried out. This arrester has more than ten times greater crack suppression effect compared with the case without the arrester, as a result of connecting upper and lower surface skins. (B6:23) Improved Damage Tolerant Face/Core Interface Design in Sandwich Structures C Berggreen (Technical Univ of Denmark) LA Carlsson (Florida Atlantic Univ) A face/core debond in a sandwich structure may propagate in the interface or kink into either the face or core depending on the mode-mixity of the loading. This study explores experimental methodologies for mapping the kinking behavior at various mode-mixities. Further, it is shown that the crack kinking behavior may be altered by changing the interface design. (B6:24) Mixed Mode Fracture Toughness Characterization of Sandwich Interfaces using the Modified TSD Specimen L Carlsson (Florida Atlantic Univ) JH Andreassen, J Jacobsen (Aalborg Univ) C Berggreen, OT Thomsen (Technical Univ of Denmark) The modified Tilted Sandwich Debond (TSD) specimen provides an improved methodology for characterization of the face/core fracture resistance. An experimental mixed mode characterization of the fracture toughness spanning the full range of phase angles has been achieved by specific steel bar reinforcements and testing over a range tilt angles. Different material configurations have been tested and compared in terms of both fracture resistance and crack path. (B6:25) Multi-Needle Stitched Composites for Improved Damage Tolerance A Aktas, P Potluri, I Porat (Univ of Manchester) In this study, stitch-bonded sandwich panels have been developed using commercial closecellular foam core and woven skins. Traditional sewing machines are not suitable for hard and thick core materials. A novel multi-needle stitch-bonding process was developed; samples were prepared, and subjected to compression, indentation and bending tests. (B6:26) Out-of-Autoclave Manufacturing of Composite Aircraft Sandwich Structures J Kratz, P Hubert (McGill Univ) The quality of sandwich structures was investigated for the out-of-autoclave prepreg processing method. The prepreg air permeability and resin rheological behaviour were characterized. Models were used to simulate the pressure inside a honeycomb core during cure. Sandwich panels manufactured under different cure conditions were tested. (B6:27) Manufacture and Mechanical Behavior of Sandwich Structures with Carbon Fiber Reinforced Pyramidal Lattice Truss Cores L-Z Wu, B Wang, L Ma, S-Y Du (Harbin Institute of Technology) NEEDS 50 WORD ABSTRACT (B6:28) L Carlsson/J Barton 11.30 Experimental Analysis of a Mechanical Joining Technology for Sandwich Elements C Warkotsch, J Feldhusen, M Benders, S Krishnamoorthy (RWTH Aachen Univ) In this paper the results of the experimental testing of a recently developed mechanical joining technology for sandwich panels are presented. The test procedure consists mainly of bending tests. Some tensile tests have also been performed. Improvements in design over the original prototypes are derived and discussed. (B6:29) Full-Scale Performance Assessment of Aircraft Secondary Sandwich Structure using Thermoelastic Stress Analysis J Barton, D Crump (Univ of Southampton) J Savage (GE Aviation) The paper presents a study of the mechanical performance of full-scale representative secondary structure sandwich panels produced using different processes. Thermoelastic stress analysis (TSA) is used to experimentally obtain the stress field and to validate FE models. (B6:30) Chiral Negative Poisson’s Ratio (Auxetic) Honeycomb Cores W Miller, C Smith, K Evans (Univ of Exeter) F Scarpa (Univ of Bristol) Characterisation of the linear elastic and anelastic, in-plane and through-thickness properties of chiral auxetic honeycombs using finite element models, benchmarked against conventional Poisson?s ratio honeycombs. Numerical models are validated using mechanical characterisation of rapid prototyped samples. In-plane and through-thickness properties are optimised according to stiffness and buckling load vs. density. (B6:31) Moisture Diffusion in Honeycomb Core Sandwich Composites M Tuttle (Univ of Washington) Thermocouples and humidity sensors were embedded within the core of a honeycomb sandwich composite panel. The panel was placed in an environmental chamber at a relative humidity of 55% and 40ºC. Core humidity levels slowly increased due to diffusion of water molecules through the composite face sheets. Measurements compare well with predictions obtained using a finite-difference analysis. (B6:32) R Mines/Y Hirose