Development of honeycomb sandwich by Zheng Chen

Sandwich panel containing Kraft paper honeycomb core and wood composite skin

Development of Novel Hollow Core Composite Panels for Value-Added Secondary Applications

By: Zheng Chen,

Faculty of Forestry, University of Toronto

http://www.valuetowood.ca/

Funded by a Value to Wood Program of Natural Resources Canada

Collaboration with University of British Columbia

FPInnovations-Forintek in Quebec city

System of project

Sample prepare and bending test in UBC

Tests of compression, shear and creep in FPInnovation-Forintek

Development of finite element (FE) model in UT

Kraft paper honeycomb panel applications in furniture industry

• Excellent strength to weight ratio• Low material cost• Smooth skin• Excellent fatigue resistance• Excellent crush strength and stiffness• Structural integrity• Exceptionally high strengths available

Project goal

To characterize the influence of parameters on the material properties of sandwich panel containing Kraft paper honeycomb core and wood composite skins for developing panels with higher ratio of stiffness to weight

Material properties evaluated





Parameters influence on material properties














Development of FE model

These FE model were developed by using the COSMOSWORK 2008 Advanced Professional (COSMOSWORK 2008 SP2.1)

Development of FE modelThe element selection for FE model

FE meshed modelLinear element

Parabolic element

Development of FE modelType of FE model developed in this

study

Development of FE modelFE model for predicting Ex



Development of FE modelFE model for predicting bending

stiffness

Development of FE modelFE model for predicting bending

stiffness

Development of FE modelProcedure of model establishment

Using data from Karademir et al (2004) as Ex and Ey of central layer of 3D FE model for all types Of honeycomb core

Obtaining Ez, Gxz and Gyz of central layer of FE model for expanded honeycomb coreby fitting the test data from Advanced Honeycomb Technologies Inc.(2007)

Using relative data from Youngquist(1999) for material properties of HB,MDF and PW skins

Obtaining Ez, Gxz and Gyz of central layer of FE model for corrugated and laminated honeycomb core by fitting the test data from FPInnovations (Chen et al 2011)

Obtaining material properties of central layer for uniform entity FE model for creep and bookshelf

Prediction the influence of parameters that the test data did not cover

Comparison of FE model predictions and test data

Edgewise compression


Edgewise compression

Note: all panels are made from expanded core and MDF skins and have 31.75 mm cell size.


Interlaminar shear loading


Interlaminar shear loading

Note: all panels are made from expanded core and MDF skins and have 31.75 mm cell size.


Flexural creep

Primary Secondary Tertiary

Creep measured in Forintek

Expanded honeycomb core and HB skin. Sample span in y direction

Note: loading level for all sample is 54.25 N


Flexural creep



FE model predictions


These FE model were developed by using the Nonlinear method and material creep effect (based on Baily-Newton law) of COSMOSWORK 2008 Advanced Professional (COSMOSWORK 2008 SP2.1)



Flexural creep




Expanded honeycomb core and HB skin. Sample span in x direction





Bookshelf under bending


Flexural fatigue


ResultsInfluence of shelling ratio and cell size

Gxz of pane with 25.4 mm size cell

Note: all panels are made from expanded core and HB skins








Gyz of pane with 25.4 mm size cell









Pane with 12.7 mm size cell

Pane with 12.7 mm size cell



Ex of pane with 12.7 mm size cell









Ey of pane with 25.4 mm size cell



Core cell size(mm)

Web thickness(mm)

Ez

(MPa)Ey

(MPa)Gyz (MPa)

Gxy

(MPa)

15.9 0.29 10.06 644.76 4.72 228.55

20.3 0.37 10.07 645.08 4.86 228.64

Note: both panels are made from 26 mm thick expanded core and 3 mm thick HB skins and have the same core density


Core density(Kg/m3)

Web thickness(mm)

Ez

(MPa)Ex

(MPa)Gxz (MPa)

Gxy

(MPa)

11.53 0.15 2.68 642.85 2.81 218.77

22.01 0.29 5.05 644.74 5.31 218.61

Note: both panels are made from 26 mm thick expanded core and 3 mm thick HB skins and have the same cell size.


Aluminium panel. 38 mm cell size, 30 kg/m3 core density,1.210-6 kg/mm2 weight


38 mm cell size, 10 kg/m3 core density,1.210-6 kg/mm2 weight

Aluminium panel. 38 mm cell size, 30 kg/m3 core density,1.210-6 kg/mm2 weight






















32 mm cell size, 10 kg/m3 core density,1.210-

6 kg/mm2 weight, longer panel





38 mm cell size, 10 kg/m3core density,1.310-6 kg/mm2 weight

ResultsInfluence of shelling ratio and cell size on flexural creep

Shelling ratio is 2

Shelling ratio is 4

Shelling ratio is 9

Shelling ratio is 12

ResultsInfluence of core structure on the stiffness of

sandwich panel

Core type Ex (MPa)

Ey(MPa)

Ez(MPa)

Gxz (MPa)

Gyz(MPa)

Gxy(MPa)

Expanded honeycomb core

644.74 642.98 5.05 5.31 2.52 218.61

Corrugated honeycomb core

669.24 641.61 6.67 12.19 1.37 217.92

Note: sandwich panel with 3 mm thick HB skin and 26 mm thick core. All core densities are 22.01Kg/m3


sandwich panel

Core type Ex (MPa)

Ey(MPa)

Ez(MPa)

Gxz (MPa)

Gyz(MPa)

Gxy(MPa)

Expanded honeycomb core

644.74 642.98 5.05 5.31 2.52 218.61

Corrugated honeycomb core

669.24 641.61 6.67 12.19 1.37 217.92

Note: sandwich panel with 3 mm thick HB skin and 26 mm thick core. All core densities are 22.01Kg/m3


sandwich panel

Type of skin material

Ez(MPa)

Ey(MPa)

Gyz(MPa)

Gxy(MPa)

HB 8.05 641.78 4.58 227.46

MDF 8.03 388.88 4.56 137.78

PL 6.57 235.5 3.9 11.7

Note: sandwich panel with 3 mm thick skin and 26 mm thick core. All core densities are 22.01Kg/m3


sandwich panel

Type of skin material

Ez(MPa)

Ey(MPa)

Gyz(MPa)

Gxy(MPa)

HB 8.05 641.78 4.58 227.46

MDF 8.03 388.88 4.56 137.78

PL 6.57 235.5 3.9 11.7

Note: Sandwich panel with 3 mm thick skin and 26 mm thick core. All core densities are 22.01Kg/m3

ResultsInfluence of core structure on flexural creep of

sandwich panel

ResultInfluence of skin type on flexural creep of

sandwich panel

ResultsInfluence of cell size on flexural creep of sandwich

panel

15.9 mm cell size

31.8 mm cell size

ResultsInfluence of curve degree and loading direction on

the bending stiffness of curved panel

ResultsInfluence of core structure and loading direction on

the bending stiffness of curved panel

ResultsInfluence of honeycomb core cell size on the

flexural fatigue of sandwich panel

ResultsInfluence of degree of curve on the impact energy

of curved sandwich panel

ResultsInfluence of degree of curve and impact orientation on

the impact energy of curved sandwich panel

ResultsInfluence of rail width of shelf on the ratio of

bending force to deflection

Shelf with rail edge

ResultsInfluence of stile width of shelf on the ratio of

bending force to deflection

Shelf with rail edgeShelf with rail edge

Shelf with stile edge

ResultsInfluence of stile and rail width of shelf on the

ratio of bending force to deflection

Shelling ratio is 2.8

ResultsInfluence of stile and rail width of shelf on the

ratio of bending force to deflection



ResultsPrimary flexural creep of shelf with different size of

rail under uniform loading

65 mm wide rail

71 mm wide rail



Note: All panels have 32 mm thick core and 3 mm thick skin

250 mm wide rail65 mm wide rail

71 mm wide rail

38 mm wide rail

10 mm wide rail



Note: All panels have 32 mm thick core and 3 mm thick skin

250 mm wide rail65 mm wide rail

71 mm wide rail

38 mm wide rail

10 mm wide rail

ResultsPrimary flexural creep of shelf with different

shelling ratio and 65 mm wide rail under uniform loading

Conclusions• Finite element (FE) models for straight and curved sandwich panels

made from Kraft paper honeycomb core and wood composite skins were developed for predicting panels’ stiffness under compression, shear force, flexural loading, creep, fatigue and impact energy. The predicted Ex. Ey, Ez, Gxz, Gyz and primary flexural creep from the FE models were in good agreement with the respective experimental results. The predicted fatigue, impact and bending behavior of straight and curved sandwich panel from these initial FE models need to be calibrated by respective experiments.

• The influences of panel’s curve degree, loading direction, core shape, core cell size, core thickness, skin thickness and skin type on these behaviors were evaluated using these developed FE models. Some key points of optimization of these honeycomb core sandwich panels (e.g. shelling ratio, core shape, core density, core orientation and cell size, curved degree and orientation, etc) were found according to these evaluations.

Conclusions• The FE models for bending and creep of bookshelves with edging

supports were developed too. The predictions from these FE models for sandwich panel four-point bending load were verified against test results. The influence of edging support size (rail and stile width) on the bending stiffness of shelf were studied using these FE models and the results indicated that bending stiffness is more sensitive to stile edgings of the shelf and shelling ratio than rail edgings. FE models for shelf under uniform flexural loading and creep need to be calibrated by further tests and the predicted results need to be confirmed by further experiments.

Acknowledgement

NRCan-Value to wood program for financial support

FPinnovations-Forintek division in Quebec city and Pof. Greg Smith and his group in the University of British Columbia and for their cooperation and assistances

Documents

Development of honeycomb sandwich by Zheng Chen