Damage Resistance Characterization of Sandwich Composites Using Response Surfaces

Lacy, Thomas E.; Samarah, Issam K.; Tomblin, John

doi:10.4271/2002-01-1538

Cited by 9 publications

(22 citation statements)

References 11 publications

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“…For such structures, numerous studies report that a relatively low energy impact event may result in face-sheet denting that is undetectable or barely detectable by visual inspection, and yet causes extensive internal damage in the form of matrix cracking, fiber fracture, face-sheet debonding and delamination, and core crushing. [3][4][5][6][7][8][9][10] If undetected, the presence of such damage in load carrying components may lead to structural failure at a fraction of design load through a combination of mechanisms including unstable dent growth, face-sheet kink-band formation and propagation, delamination buckling and growth, and compressive fiber fracture. [6][7][8][10][11][12][13][14][15][16][17] The extent of internal damage, occurrence of a particular failure mode, and degradation of strength are generally dependent on factors including face sheet and core materials, face-sheet thickness and stacking sequence, core density and thickness, interface properties between face sheet and core, severity of impact, indentor geometry, and method of sandwich fabrication.…”

Section: Introductionmentioning

confidence: 99%

Compressive strength of honeycomb-stiffened graphite/epoxy sandwich panels with barely-visible indentation damage

Czabaj

Zehnder

Davidson

et al. 2013

Journal of Composite Materials

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This study examines the parametric effects of core density, core thickness, face-sheet stacking sequence, and indentor diameter on the compressive strength of aluminum honeycomb-core sandwich panels stiffened with eight-ply, quasi-isotropic, graphite/epoxy face sheets. The sandwich panels contained damage at the threshold of visual detectability created through quasi-static indentation with 25.4 mm or 76.2 mm-diameter spherical indentors. During compression-after-indentation testing, failure occurred due to: dent deepening followed by localized, compressive micro-buckling of fibers in the 0° plies; localized buckling of the near-free-surface sub-laminates; or unstable dent growth in the direction lateral to the applied compressive load. Regardless of failure mode or face-sheet type, the compression-after-indentation strength increased with increasing core thickness and with decreasing core density. Additionally, panels containing face sheets with the 0° plies near the mid-plane and 45° angle change between subsequent plies exhibited greater undamaged compressive strength and higher compression-after-indentation strength relative to panels containing 90° angle changes between subsequent plies and 0° plies near the free surface. The compression-after-indentation strength was found to be relatively unaffected by the indentor diameter size and the resulting variations in the face sheet and core damage. These results imply that precise representation of the damage state in models to predict the post-indentation response of sandwich panels may not be necessary in order to make accurate average residual strength predictions.

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Section: Introductionmentioning

confidence: 99%

Compressive strength of honeycomb-stiffened graphite/epoxy sandwich panels with barely-visible indentation damage

Czabaj

Zehnder

Davidson

et al. 2013

Journal of Composite Materials

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“…5,6 For the compressive fiber failure mode, the fibers in the impacted facesheet buckle during compressive loading. A thin band of compressive failure then suddenly propagates across the width causing ultimate failure.…”

Section: Introductionmentioning

confidence: 99%

“…[4][5][6][8][9][10][11] Parameters that affect the damage introduced in sandwich composites and the post-impact compressive strength include indenter shape and size, impact load, facesheet toughness, facesheet stacking sequence and thickness, core density and thickness and fabrication technique. 2,[4][5][6] Indenter geometry and size can significantly affect the induced damage and post-impact compressive strength. Common indenters used in experimental studies included flat-ended, conical or spherical shapes.…”

Section: Introductionmentioning

confidence: 99%

Compressive strength of aluminum honeycomb core sandwich panels with thick carbon–epoxy facesheets subjected to barely visible indentation damage

Hasseldine

Zehnder

Keating

et al. 2015

Journal of Composite Materials

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An experimental study of damage tolerance under quasi-static indentation (QSI) was performed for sandwich composite panels consisting of 16-ply carbon-epoxy facesheets bonded to an aluminum honeycomb core. To determine how indentation damage and compression strength after indentation depend on the facesheet layup, three facesheet stacking sequences were used, varying the maximum ply angle change and placement of the outermost 0 ply. Similarly, to determine the effect of core parameters on damage and strength following indentation, three cores with varying density and thickness were studied. Specimens were indented in QSI to the barely visible indentation damage threshold by spherical indenters of 25.4 or 76.2 mm diameters. Damaged specimens were tested to failure in compression to determine the post-indentation compressive strength and resulting failure mode. Compression-after-indentation (CAI) strength is compared to the undamaged strength obtained from edgewise-compression tests of specimens with the same geometry type. Three distinct failure modes were observed in the CAI experiments: compressive fiber failure, delamination buckling and global instability. Post-indentation compressive strength was independent of indenter size and there was no clear propensity for a particular failure mode dependent on a given specimen geometry. Specimens with a high core density and facesheets with a primary ply angle change of 90 were found to be the most damage resistant. Specimens with facesheets having the outer 0 plies closest to the center of the laminate were found to be the most damage tolerant.

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“…Statistical design of experiment techniques may be used to identify and model complex relationships between input design factors and output responses in material systems. With polymer composites, these statistical techniques have previously been used for dynamic mechanical analysis, Izod impact testing of VGCNF/VE nanocomposites, and damage characterization of sandwich composites by isolating and examining the effects of multiple input design factors. The relationships between these factors can be statistically explored by developing response surface models (RSMs) to determine the estimated responses within the design boundaries.…”

Section: Introductionmentioning

confidence: 99%

Creep characterization of vapor‐grown carbon nanofiber/vinyl ester nanocomposites using a response surface methodology

Drake

Sullivan

Lacy

et al. 2015

J of Applied Polymer Sci

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The effects of selected factors such as vapor-grown carbon nanofiber (VGCNF) weight fraction, applied stress, and temperature on the viscoelastic responses (creep strain and creep compliance) of VGCNF/vinyl ester (VE) nanocomposites were studied using a central composite design (CCD). Nanocomposite test articles were fabricated by high-shear mixing, casting, curing, and post curing in an open-face mold under a nitrogen environment. Short-term creep/creep recovery experiments were conducted at prescribed combinations of temperature (23.8-69.2 C), applied stress (30.2-49.8 MPa), and VGCNF weight fraction (0.00-1.00 parts of VGCNF per hundred parts of resin) determined from the CCD. Response surface models (RSMs) for predicting these viscoelastic responses were developed using the least squares method and an analysis of variance procedure. The response surface estimates indicate that increasing the VGCNF weight fraction marginally increases the creep resistance of the VGCNF/VE nanocomposite at low temperatures (i.e., 23.8-46.5 C). However, increasing the VGCNF weight fraction decreased the creep resistance of these nanocomposites for temperatures greater than 50 C. The latter response may be due to a decrease in the nanofiber-to-matrix adhesion as the temperature is increased. The RSMs for creep strain and creep compliance revealed the interactions between the VGCNF weight fraction, stress, and temperature on the creep behavior of thermoset polymer nanocomposites. The design of experiments approach is useful in revealing interactions between selected factors, and thus can facilitate the development of more physics-based models.

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Damage Resistance Characterization of Sandwich Composites Using Response Surfaces

Cited by 9 publications

References 11 publications

Compressive strength of honeycomb-stiffened graphite/epoxy sandwich panels with barely-visible indentation damage

Compressive strength of honeycomb-stiffened graphite/epoxy sandwich panels with barely-visible indentation damage

Compressive strength of aluminum honeycomb core sandwich panels with thick carbon–epoxy facesheets subjected to barely visible indentation damage

Creep characterization of vapor‐grown carbon nanofiber/vinyl ester nanocomposites using a response surface methodology

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