Performance of composite sandwich structures under thermal cycling

2019 ◽  
Vol 54 (2) ◽  
pp. 271-283
Author(s):  
Sandesh Rathnavarma Hegde ◽  
Mehdi Hojjati
Keyword(s):  
Crack Formation ◽  
Mechanical Performance ◽  
Crack Density ◽  
Free Edge ◽  
Element Analysis ◽  
Thermally Induced ◽  
Composite Sandwich ◽  
Composite Sandwich Structures ◽  
Number Of Cycles ◽  
Microscopic Inspection

Effect of thermally induced microcracks on mechanical performance of a space grade laminated sandwich panel is investigated. A simple non-contact setup using liquid nitrogen is developed to subject the material to low temperature of −170℃ with cooling rate of 24℃/min. Then the samples are exposed to the elevated temperature of 150℃ inside oven. Microcracks formation and propagation are monitored through microscopic observation of cross-section during the cycling. Flatwise tensile test is performed after a number of cycles. A correlation is made between number of cycles and flatwise mechanical strength after quantifying the microcracks. It is observed that the crack formation gets saturated at about 40 cycles, avoiding the need to conduct more thermal cycles. Microcrack formation both at the free edge and middle of laminate was observed. The crack density at the middle was comparatively less than the ones found on the free edges. Results for non-contact cooling are compared with samples from direct nitrogen contact cooling. Microscopic inspection and flatwise test show differences between contact and non-contact cooled samples. Flatwise tensile strength for non-contact cooled samples shows 15% reduction, while the contact cooled samples have about 30% decrease in bond strength. A 3D finite element analysis is conducted to qualitatively identify the location of stress concentration which can be possible sites of crack formation. Good agreement is observed between the model and experimental results.

Thermally induced microcracks and mechanical property of composite honeycomb sandwich structure: Experiment and finite element analysis

2018 ◽  
Vol 22 (8) ◽  
pp. 2544-2566 ◽  
Author(s):  
Sandesh Rathnavarma Hegde ◽  
Mehdi Hojjati
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Mechanical Strength ◽  
Sandwich Structure ◽  
Crack Density ◽  
Thermal Cycles ◽  
Element Analysis ◽  
Honeycomb Sandwich ◽  
Number Of Cycles ◽  
Honeycomb Sandwich Structure

Microcracking in composite honeycomb sandwich structure and its effect on mechanical properties are studied in this paper. A methodology is presented to study the extent of mechanical strength degradation of composite sandwich structure, subjected to thermal fatigue. The material under study is used for spacecraft structural applications. The test coupons were exposed to thermal cycling at elevated temperature as high as +150°C inside the oven and cryogenic temperature of −190°C by dipping in liquid nitrogen, which is comparable to the thermal environment experienced by spacecraft structures. After each thermal cycle, coupons were inspected for microcracks under an optical microscope at the cross section. The microcracks were then quantified using parameters like crack length and crack density with increase in the number of cycles. Flatwise tensile test was conducted on the coupons after every 10 thermal cycles, up to 60 cycles, to make a correlation between crack density and mechanical strength. It was observed that by increasing the number of thermal cycles, the crack density increases and the flatwise tensile strength decreases up to a specific number of cycles. Finite element analysis was performed to predict the possible location of microcracks formation and compared with experimental observation. Good correlation was observed.

Thermal buckling of a thin uniform circular disk: a comparison of predictions

2006 ◽  
Vol 110 (1112) ◽  
pp. 691-693
Author(s):  
K. A. Seffen
Keyword(s):  
Boundary Layer ◽  
Finite Element Analysis ◽  
Exact Solution ◽  
Approximate Solution ◽  
Circular Disk ◽  
Free Edge ◽  
Edge Condition ◽  
Constant Thickness ◽  
Element Analysis ◽  
Thermally Induced

AbstractThe conditions for thermally-induced buckling of an unloaded thin, circular disk are compared from two well-known but unconnected studies: an approximate solution by Freund for a constant thickness disk, which must neglect the free edge condition, and an exact solution by Mansfield but only for a disk whose thickness tapers to zero in a particular manner. It is shown that buckling occurs at slightly higher values compared to a finite element analysis of a constant thickness disk but that the case of variable thickness seems to offer a closer result, which suggests that it better models the boundary layer behaviour near the free edge.

Infill shape effects on bending stiffness of additively manufactured short fibre reinforced polymer sandwich specimens

2021 ◽  
pp. 073168442110201
Author(s):  
Luca Michele Martulli ◽  
Pablo Barriga Ruiz ◽  
Akshay Rajan ◽  
František Bárnik ◽  
Milan Sága ◽  
...  
Keyword(s):  
Composite Structures ◽  
Sandwich Beam ◽  
Bending Stiffness ◽  
Element Analysis ◽  
Composite Sandwich ◽  
Composite Sandwich Structures ◽  
Reinforced Polymer ◽  
The Finite Element Analysis ◽  
Shape Effects ◽  
Fibre Reinforced Polymer

Additively manufactured polymer parts are often designed like composite sandwich structures. In this work, sandwich beam-like specimens with hexagonal, triangular and rectangular infills were manufactured with different infill densities. An influence of the shape of the infill on the overall stiffness was observed. The bending stiffness of the hexagonal specimens was between 13% and 25% lower than that of the other two cases that instead showed similar performances. Numerical simulations were performed using both shell and solid elements for the infill, to check if it was possible to model the differences observed experimentally. All simulations lead to accurate bending stiffness predictions, except for the rectangular infills with higher infill densities, for which overprediction between 20% and 25% was obtained. Based on these results, strategies for the finite element analysis of additively manufactured composite structures are discussed.

Effects of honeycomb core damage on the performance of composite sandwich structures

2019 ◽  
Vol 54 (16) ◽  
pp. 2159-2171
Author(s):  
William T King ◽  
William E Guin ◽  
J Brian Jordon ◽  
Mark E Barkey ◽  
Paul G Allison
Keyword(s):  
Finite Element ◽  
Shear Modulus ◽  
Composite Structures ◽  
Sandwich Structures ◽  
Honeycomb Core ◽  
Element Analysis ◽  
Composite Sandwich ◽  
Core Damage ◽  
Composite Sandwich Structures ◽  
Aluminum Honeycomb

This work presents an experimental and numerical investigation of the effects of pre-existing core damage on aluminum honeycomb core composite sandwich structures. Quasi static flexural and compression experiments were performed, where the effects of core damage on the shear modulus and Young's modulus were quantified. In addition, finite element analysis was performed on the sandwich structures to elucidate the effects of the core damage on the structural response. Comparisons of experimental and finite element responses are presented for sandwich structures consisting of carbon fiber facesheets and an aluminum honeycomb core. The pre-existing core damage is observed to cause up to an 8% reduction in shear modulus and a 9% reduction in elastic modulus. It is also determined that the presence of pre-existing core damage results in an asymmetrical compressive load distribution in the composite structures.

A theoretical formulation of the buckling analysis of a composite sandwich structure with multiple holes

2021 ◽  
pp. 109963622110255
Author(s):  
Yongha Kim ◽  
Jungsun Park
Keyword(s):  
Sandwich Structure ◽  
Sandwich Plate ◽  
Homogenization Method ◽  
Buckling Analysis ◽  
Element Analysis ◽  
Theoretical Formulation ◽  
Composite Sandwich ◽  
Aerospace Applications ◽  
Composite Sandwich Structures ◽  
Multiple Holes

This article presents a theoretical formulation presented for conducting a buckling analysis of the composite sandwich plate with multiple holes via the homogenization method. The validity of the theoretical formulation was verified by comparing the results of the finite element analysis and experimental analysis. Finally, the theoretical formulation was used to optimize a composite sandwich plate with multiple holes for the design of an aircraft structure to minimize the mass. The optimization result allows a database to be obtained on the buckling characteristics of composite sandwich structures with multiple holes for applying aerospace applications. We then concluded that the theoretical formulation is well-suited to buckling analysis of a composite sandwich structure with multiple holes for aerospace applications due to their relative simplicity and computational efficiency.

Mechanical performance of CF/PEEK–PEI foam core sandwich structures

2017 ◽  
Vol 21 (8) ◽  
pp. 2680-2699 ◽  
Author(s):  
Jonas Grünewald ◽  
Patricia P Parlevliet ◽  
Alexander Matschinski ◽  
Volker Altstädt
Keyword(s):  
Mechanical Performance ◽  
Sandwich Structures ◽  
Cell Structure ◽  
Processing Parameters ◽  
Thermoplastic Composite ◽  
Composite Sandwich ◽  
The Core ◽  
Composite Sandwich Structures ◽  
Cell Structures ◽  
Original Cell

Previous work showed that thermoplastic composite sandwich structures offer great potential to meet the demands of lightweight structures for aviation applications. In this study, the influence of several processing parameters on the mechanical properties of thermoplastic sandwich components, consisting of carbon fibre reinforced polyetheretherketone skins and polyetherimide foam cores, is characterised. Sandwich specimens are manufactured with varying skin temperatures, core compaction distances and different polyetherimide concentrations at the skin–core interface. Following, sandwich samples are mechanically tested to characterise the bond strength, the core performance as well as the performance of the whole sandwich. The results show that in most cases the processing parameters significantly affect the cell structure of the sandwich core, provided that a proper fusion bond between skins and core exists. Thereby, the core performance seems to be weakened and failure predominantly occurs in the transition between affected and original cell structures.

Modified foam cores for full thermoplastic composite sandwich structures

2017 ◽  
Vol 21 (3) ◽  
pp. 1150-1166
Author(s):  
Jonas Grünewald ◽  
Tilman Orth ◽  
Patricia Parlevliet ◽  
Volker Altstädt
Keyword(s):  
Mechanical Performance ◽  
State Of The Art ◽  
Sandwich Structures ◽  
Thermoplastic Composite ◽  
Foam Core ◽  
Cycle Times ◽  
Composite Sandwich ◽  
Current State ◽  
Composite Sandwich Structures ◽  
Honeycomb Cores

Full thermoplastic composite sandwich structures with a foam core offer the possibility to be manufactured by fusion bonding in significant shorter cycle times than thermoset-based sandwiches. However, the application of foam cores results in lower mechanical properties such as compression and shear strength compared to honeycomb cores, therefore foam-based sandwiches cannot compete with sandwich structures based on Aramid/phenolic honeycomb cores, the current state of the art. In order to improve the mechanical performance of foam core-based sandwiches while maintaining their advantages, concepts to reinforce the foams were developed in this study. By introducing rods either orthogonally or diagonally to the skin plane, which are fusion bonded to the skins during processing, the compression and shear properties can be improved by up to 1000% and 72%, respectively. Even when correcting for the weight increase, an improved specific compression strength could be achieved. And therefore, the pinning looks especially promising when only applied locally in highly loaded areas for example.

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