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