Performance Feature Characteristics
Competitive Sandwich Panel Comparison
Designing Structural and Non Structural PCT Panels
Thermoforming PCT Honeycomb Core Substrates
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Translucent PCT PC Core | Side View Translucent PCT PC Core | Opaque PCT HIPS Core |
PCT High Impact Polystyrene PepCore TM · High Strength to Weight Ratio · Exceptional Strength to Weight Ratio | PCT Polypropylene PepCore TM · Excellent Chemical Resistance · High Strength to Weight Ratio |
VG – Very Good
G – Good
F – FairP – Poor
Composite honeycomb sandwich structures have been successfully manufactured and used in numerous applications for many years with the prime objectives for their use being weight reduction, increasing stiffness and reducing overall manufacturing costs.
PCT composite honeycomb sandwich panels have exceptional load bearing capabilities either in static or dynamic configurations due to the unique structure of the honeycomb material as well as other factors. Traditional composite honeycomb panels are manufactured with various facings and honeycombs that are manufactured with a standard vertical cell wall configuration which when bonded together act as an “I” beam. The facings take the bending loads, one in compression the other in tension. The vertical configuration of traditional honeycombs resist the shear loads developed, increasing the overall rigidity of the panel by spreading the facing apart.
PCT composite honeycomb sandwich panels are also manufactured with various facings but with a unique honeycomb configuration that has truss shaped cellular walls with a surrounding flange area around each cell. This unique and structurally sound configuration allows for stresses to be distributed laterally in the structure which ultimately produces an extremely rigid structure that is capable of sustaining large loads without catastrophic failures. The surrounding flange areas around each cell creates a significantly greater bonding area for the honeycomb which also aids in distributing these stresses thus producing a uniquely rigid structure.
PCT composite sandwich panels should be designed to meet the following structural criteria for specific load considerations:
Ø The PCT composite panel should have sufficient flexural and shear rigidity to minimize the overall deflection of the panel under specific loads.
Ø The honeycomb used should be of sufficient thickness and have sufficient shear modulus to prevent buckling of the panel under specific loads.
Ø The facing materials used should be of sufficient thickness so as to withstand shear, tensile and compressive stresses produced under specific loads.
Ø Adhesives used should have adequate strength to carry the shear stresses into the honeycomb structure.
Ø The honeycomb chosen should have sufficient compressive strength so as to resist crushing of the honeycomb by compressive stresses produced through flexural bending and loads acting perpendicular to the facing materials of the panel.
Ø Honeycomb and facings chosen should have sufficient compressive modulus to prevent wrinkling of the faces under specific loads.
The overall deflection of a composite honeycomb sandwich panel is determined by adding the deflection produced by the bending and shear reaction of the sandwich structure. The overall panel deflection is dependent on the flexural modulus of elasticity of the facing materials and the core shear modulus of the honeycomb used. To determine the overall deflection (Δ) of a flat composite sandwich panel beam with the same facing materials the following equation is used:
(Δ ) = 2 Kb P L³ λ + Ks P L
Ef Tf h² b h Gc b
(Bending Deflection) (Shear Deflection)
Where:
Kb = Bending Deflection Constant P = Total Load (Lbs.) L = Span (Inches)
λ = Moment of Inertia - μ² μ = Poisson's Ratio of facing Ef=Facing Modulus of Elasticity (PSI)
Tf = Facing Thickness (Inches) b = Width (inches)
h=Centroid Distance(Inches)=(Thickness Face 1)/2+(Thickness Face 2)/2+Thickness of core
Gc = Core Shear Modulus (PSI) Ks = Shear Deflection Constant
The following charts show the deflection of panels constructed from PCT R High Impact Polystyrene faced with 0.032” aluminum on both sides under uniform static loadings. The thicknesses tested were: 1.0”, 1.25”, 1.50”, 1.75” and 2.00”. The panel size tested was 46.125” x 94.25” and was supported on all four sides( Chart #1). Chart #2 shows the same panels supported on all four sides and at the center of the panels.
The following table describes typical Composite Sandwich Beam Structures and the Bending and Shear Constants used to calculate the overall deflection
| Type of Beam Structure | Bending Deflection Constant (Kb) | Shear Deflection Constant (Ks) |
| Uniform Load-Simple Support on Two Sides | 0.01302 | 0.125 |
| Uniform Load-Both Ends Fixed | 0.002604 | 0.125 |
| Center Load- Simple Support on Two Sides | 0.02083 | 0.25 |
| Center Load- Both Ends Fixed | 0.00521 | 0.250 |
Uniform Load-Cantilever Support | 0.125 | 0.5 |
| End Loaded- Cantilever Support | 0.3333 | 1 |
| Uniform Load- One End Fixed and One End Simply Supported | 0.005405 | 0.07042 |
Other considerations that should be taken into account when designing PCT honeycomb composite panels are as follows:
Ø Temperature conditions at which panels will be subjected to.
Ø Flammability and smoke generation requirements of the panels.
Ø Humidity or moisture conditions that panels will be subjected to.
Ø Type of facings to be utilized for either structural, cosmetic or other considerations.
Ø Types of adhesive to be used on the panels.
Ø Thermal resistance requirements of the panels.
Ø Acoustical or sound absorption/deadening characteristics required.
Ø Type of close-out design for edges of panels, such as wood, metal, plastic, extrusion, etc.
Ø Type of panel reinforcement for areas with high or concentrated loadings.
Ø Fastening or attachment requirements.
Ø Budgetary costs of panels and labor costs for installation.
Ø Weight limitations of the panels.
One of the most important and critical considerations in designing a good PCT composite sandwich panel is the selection of an appropriate close-out for the edges of the panel. The close-out serves a number of purposes such as:
The following are some of the most typical types of edge close-outs that can be utilized
On occasion, PCT composite honeycomb sandwich panels need to be attached to one another or to other structures. Typically the panels can be attached to each other by various means such as tongue and groove, use of special extrusions that lock the panels together, use of “C” or “H” channel extrusions or tube extrusions which allow the panels to be attached to each other either by mechanical fastening or adhesive bonding. Other means of attaching panels to each other or to other structures is by use of a “ship lap construction” as depicted by the following diagram:
Panels may also be attached to other structures using the same means as stated previously or by use of inserts that may be potted into the panels for ease of attachment to other structures. These threaded inserts are installed into the rear of the panel as follows before the front face is laminated:
1. Drill body size hole of the insert through the rear facing in areas required. Do not
drill through the front facing if one is present.
2. Counter bore flange diameter to the required depth.
3. Tape or secure insert in place so it is in the location required.
4. Pour epoxy mixture around insert making certain to use an epoxy that has sufficient
working time.
5. After the epoxy is cured (5-15 minutes) remove the tape.
6. Laminate top or front face to the PCT honeycomb.
On occasion, PCT panels may be subjected to concentrated loadings or various types of hardware need to be attached to panels for a multitude of reasons. When one is confronted with these problems, PCT panels may be reinforced in specific areas. There are a number of configurations that can be utilized so as to reinforce the panels for concentrated loading applications or if various hardware needs to be attached. Some typical panel reinforcement configurations are:
· Filling the core with either Epoxy, EVA, Durham’s Rock Hard Water Putty or any
other suitable material that will fill the cells and cure or solidify after a short period
of time.
· Cut out the area in the core where reinforcement is required and bond a solid block
of wood, metal, plastic or high density foam in place.
· Cut out the area in the core where reinforcement is required and bond a extruded
metal or plastic tube, channel or other specified extruded shape.
The following diagrams depict the reinforcement configurations stated
Polymer Core Technologies honeycomb core substrates can be thermally shaped or formed into numerous configurations using either strip bending, drape forming or vacuum forming techniques. Because of the unique structures of the cores, various shapes can be obtained without adversely affecting the physical properties of the core substrate structures. The three most commonly used methods of thermoforming PCT core substrates are briefly described as follows:
· Strip bending is essentially accomplished by heating the PCT core at the bending point required using a strip heater and then transferring the substrate to a fixture, tool or mandrel that provides the desired configuration. Pressure is applied at the heated bending point of the core until the required configuration is achieved. Pressure is maintained on the tool until the part is cooled to room temperature. PCT HIPS should be heated to a minimum 215°F, PCT PC to 305°F, PCT PP to 275°F and PCT PVC to 180°F. Care must be taken not to overheat the core to prevent collapse of the core structure.
· Drape forming is performed by heating the PCT core using IR lamps or an oven followed by draping the core over a tool/mold followed by minimal pressure to assure the core is formed into the required shape. Pressure is maintained on the tool until the part is cooled to room temperature. PCT HIPS should be heated to approximately 215-255°F, PCT PC to 305-355°F, PCT PP to 275-325°F and PCT PVC to 180-230 °F. Care must be taken not to overheat the core as with strip bending.
· Vacuum forming is accomplished by heating the PCT core using IR lamps or an oven, placing the core into a vacuum forming machine with tool/mold, clamping the core down onto the tool and drawing the core over the tool with a downward motion until a seal is created. Vacuum is applied causing the core to form over the tool/mold by a pressure differential. The part is held onto the mold/tool and cooled to room temperature. The same temperatures and precautions previously mentioned are utilized to form the core materials and to prevent collapse of the core structures.
The above descriptions and conditions are basic guidelines for thermoforming PCT core materials. Modifications may be required based on part geometry/configuration, equipment utilized, process conditions and part thickness.
Thermoforming Images | ||
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Various Thermoformed Components |
| Additional Thermoformed Components |