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The integration of inserts into sandwich panel constructions is a complex multi-step process with significant human intervention that also limits the geometrical freedom of the insert design. In a standard sandwich construction, the panel core is made up of multiple materials across its main components: insert, potting and core. This multi-material assembly is not only difficult to manufacture, but it also promotes stress jumps at the insert-core interface, leading to a sub-optimal load distribution from the bolt to the panel core. Additive manufacturing (AM) can lead to a single-part core and insert assembly with more optimised insert geometries that can better transmit the loads applied to the panel. Previous work by the authors has explored the manufacturing limits and the failure modes of AM inserts integrated in cores printed out of sintered AlSi10Mg. The conclusions were that the core walls and insert elements should have a minimum design thickness of 0.5 mm to survive the tapping process without facesheets attached and it was found that the main failure mode of the geometries tested in pull-out was buckling of the insert walls. Based on these results, the paper proposes a novel insert design philosophy that can delay the buckling of 3D printed inserts and move the failure point of the insert away from the bolt. A set of inserts that follow this design direction is manufactured and tested under normal pull-out loads and the optimised designs outperform standard printed insert geometries by a factor of three. The design philosophy can be further developed to offer a suitable alternative to the current insert standard. [ABSTRACT FROM AUTHOR]

Aluminium honeycomb core is a thin-walled cellular structure extensively used in crash resistance applications in automotive industry. To overcome current challenges in adhesive-bonded honeycomb, new fabrication route using micro friction stir lap welding has been proposed. With a specific energy absorption capacity as high as 28.2 kJ/kg in flatwise impact testing, fabricated honeycomb demonstrated its potential for industrial applications. The structure exhibited no weld cracks or cell wall delamination, unlike adhesive-bonded honeycombs. However, in friction stir welding of thin sheets (0.5 mm), achieving an optimized heat input is challenging due to limited scope for variation in process parameter and tool design. Therefore, control of heat outflow by proper selection of backing plate material is the alternative approach for achieving desirable joint performance. Experiments with backing plates having a range of thermal diffusivities demonstrated that joint produced with mild steel backplate exhibited maximum shear-tensile strength. Conversely, joint with aluminium backplate exhibited poor plastic flow of material. Effective sheet thickness and lap width were predominantly affected by heat accumulation in weld, resulting in different failure modes. [ABSTRACT FROM AUTHOR]

Sandwich panels are the fundamental structural element in a wide range of applications, including in satellite primary structures. While sandwich constructions are very efficient, their complex multi-material assembly leaves room for further optimisation of the core volume and improvement in the integration phase. One key technology that can enable the transition to multifunctional sandwich panel cores tailored to certain applications is the additive manufacturing (AM) of satellite primary structure sandwich panel cores. This paper investigates the feasibility of replacing the baseline Aluminium honeycomb core with a core printed out of AlSi10Mg through Powder Bed Fusion. Sandwich panels with carbon fiber-reinforced plastic (CFRP) facesheets and printed honeycomb cores as well as fully printed corrugated panels are produced and tested under three point bending (3PB) and compression as part of the EU funded ReDSHIFT project. The Instron 5560 (3PB) and 4204 (compression) are used to perform the experiments that follow the ASTM C393-11 and C365 standards. When compared against the baseline CFRP-AL panels, the 3D printed honeycomb cores carry up to twice as much load per unit mass in bending and four times as much in compression, while also being stiffer. The fully printed corrugates samples are weaker than the honeycombs, but in conjunction with the honeycomb geometry may present a promising avenue for developing multifunctional cores. While limitations with current metal printing technology prevent AM cores from matching the mass of baseline designs, the superior specific performance and geometrical freedom make printed cores a promising design alternative. [ABSTRACT FROM AUTHOR]

This paper investigates the method for water ingress detection in an aluminum honeycomb sandwich structure by laser ultrasonics. To clarify the propagation of Scholte waves generated at the solid-liquid interface, the theoretical dispersion curves in the water-aluminum layered structure are calculated by the global matrix method. Using a laser ultrasonic visualizing inspector, the guided wave propagation in the wavefields has been visualized, which shows the mode conversion behaviors occurring in the water ingress area. The clarification of mode conversion is then investigated by the finite element method. The Scholte modes at the solid-fluid interface and the Lamb modes in the face sheet are interconverted because of the change in the waveguide structure. Wavenumber filter reconstruction and the resulting energy maps are applied to illustrate the mode conversion in the wavefields and to detect the water ingress area. Results show that the appearance of the water layer contributes to the mode conversion behaviors during the guided wave propagation in the honeycomb sandwich structure, which offers the potential for water ingress detection based on the mode conversion behaviors. [ABSTRACT FROM AUTHOR]

A circular honeycomb lower limb protection device was proposed to reduce the damage to the occupant's lower limbs under a vehicle under-belly blast. First, a local equivalent model of the occupant-restraint system was established, and drop impact tests and theory were used to validate the model's accuracy. Then, under the same mass, the protection performance of eight lower limb protection devices using circular honeycomb, hexagonal honeycomb, reentrant honeycomb, etc., as sandwiches were compared. It was found that the lower limb protection device with a circular honeycomb sandwich provides the best defence for lower limbs. Subsequently, the effect of gradient structure settings and dimensional parameters on the protection performance of circular honeycomb lower limb protection devices was investigated. Finally, multi-objective optimization has been carried out to further improve its protection performance. The results indicated that the protection performance of the lower limb protection device could be effectively improved by reasonably selecting the cell arrangement, gradient type and gradient interval of the honeycomb sandwich. When the optimized lower limb protection device was employed, the occupant's left and right lower tibial peak forces were decreased to 3.67 kN and 3.55 kN, respectively. Compared with the initial design, the optimized lower limb protection device reduced the left and right lower tibial peak forces by 21.1% and 23.8%, respectively, and the total mass decreased by 51.5%. [ABSTRACT FROM AUTHOR]

The honeycomb sandwich panel presents a highly promising solution for enhancing ballistic behavior owing to its excellent strength-to-weight ratio and impact resistance. This study focuses on investigating the shock mitigation properties of honeycomb sandwich panels through experimentation and numerical simulation of high-velocity impact tests. Single-scale and double-scale hierarchical honeycomb cores are manufactured using selective laser melting with AlSi10Mg powder, combined with a pair of stainless steel (SS 316) sheets. High-velocity impact experiments were conducted within a velocity ranging from 100 to 270 m/s to examine the effects of different cores and projectile nose shapes on the dynamic response of the panels. Numerical simulations using ABAQUS/Explicit software were performed and validated against the experimental results. The sandwich panel with a double-scale hierarchical honeycomb core exhibited 7.8% and 6.1% more energy absorption compared to the single-scale hierarchical honeycomb core against conical and hemispherical nose projectiles, respectively. Additionally, the ballistic limit for the hemispherical projectile was found to be 8.9% higher than the conical-nose projectile under the same impact velocity and panel thickness. Moreover, an increase in panel thickness from 12 mm to 25 mm prompted a significant improvement of approximately 39% in specific energy absorption and a 44% increase in ballistic limit velocity. These findings highlight the considerable potential of single-scale and double-scale hierarchical honeycomb sandwich panels for the development of threat-resistant structures in critical dynamic loading applications. [ABSTRACT FROM AUTHOR]

The flatwise compression and mechanical response of gradient-tandem Nomex honeycomb sandwich panels were investigated by quasi-static compression tests. Finite element models of the gradient-tandem Nomex honeycomb sandwich panels were established to evaluate the effects of layer sequences, separator materials, and layer heights on the mechanical properties through parametric studies. The different assembly of honeycomb sequence and separator material affected the deformation sequence and peak stress of the sandwich panels. Under quasi-static compression, the response curves are smoother when the appropriate separator material and assembly sequence are chosen. Meanwhile, the peak stresses are effectively reduced. The research results can guide the individualized design of tandem Nomex honeycomb sandwich panels. [ABSTRACT FROM AUTHOR]

The failure behavior and load-carrying capacity of Nomex honeycomb sandwich panels under three-point bending are experimentally and numerically studied. The failure modes observed in experiments are core shear failure and face-sheet/core debonding. A detailed model considering Nomex paper and resin coating is built with Abaqus/explicit simulation. The Hill 1948 quadratic anisotropic yield criteria are adopted to describe the plastic behavior of Nomex paper and the principal stress criteria are used for predicting the failure of resin coating. The effectiveness of the proposed meso-scale model is validated by comparing the experimental and the numerical results. The effects of geometric parameters on the bending behaviors are discussed in detail. It is shown that the ultimate force and bending stiffness of Nomex honeycomb sandwich panels is significantly influenced by the core orientation, resin thickness and cell size. The cutting position has no effect on the ultimate force and bending stiffness. [ABSTRACT FROM AUTHOR]

Honeycomb cores made of phenol resin impregnated paper are widely used in sandwich structures of aircraft. Owing to the rather weak core material, this kind of sandwich is prone to a range of damages as a result of impact loading which may accidentally occur during operation. When employed in aircraft these structures have to be damage tolerant. This means barely visible damages have to be considered in the structural design process. In the standard design process for damage tolerant aircraft structures especially the effect of impacts has to be considered but is mostly investigated on unloaded sandwich components. However, aircraft structures are not completely stress free, even when the aircraft is in parking position. At least the structural weight will cause a permanent static preload. In the literature there are only few investigations dealing with the impact behaviour of preloaded honeycomb sandwich structures. In general, studies on composite structures have shown that tension preloads lead to higher structural impact resistance, while prestressing in compression reduces mechanical properties such as impact strength and stiffness of the structure. For this reason, a compression preload is considered as the more critical load case. In order to evaluate the effect of static compression preloads an experimental study on five different honeycomb sandwich configurations was conducted. The experimental investigations showed that even low preloads cause a higher structural damage area, which results in a lower residual strength of the structure. The results indicated that it is recommendable to consider structural compression preloads in the aircraft structural design process. [ABSTRACT FROM AUTHOR]

By utilizing 3D printing technology, experimental three-point bending (TPB) tests, and finite element analysis, six honeycomb structures with a variety of overall Poisson's ratios (PR) are studied and compared in terms of bending properties and failure mechanisms. Four novel honeycombs that are designed by hybridizing hexagonal and re-entrant units outperform benchmark conventional honeycombs in terms of load-carrying capacity. Architected hybrid geometry honeycombs with zero PR show excellent specific energy absorption capability in comparison to benchmark honeycombs, absorbing approximately 136.9% and 475.1% more energy under TPB. 3D-printed honeycombs consisting of hexagonal units face layer separation damage mode under bending, while honeycombs with re-entrant cells in their lattice fail with joint shear due to the angle of their struts towards loadings. Designing honeycombs with a hybrid geometry lattice can enhance the load-carrying capacity, specific energy absorption, flexibility, and flexural modulus of the structure under bending. Due to their superior performance, the proposed architected hybrid geometry honeycombs with various Poisson's ratios own promising applications in automotive, protective, and construction industries. [ABSTRACT FROM AUTHOR]

This study presents experimental results of compression after impact (CAI) testing of aluminum honeycomb core sandwich structure with face sheets made of co-cured T1100/3960 quasi-isotropic carbon/epoxy when tested at +22.5⁰ and −22.5⁰ with respect to the 0⁰ fibers. In a previous study examining the CAI strengths of honeycomb sandwich structure, it was found that specimens had different CAI strengths, based on a [−45/90/+45/0]S layup, depending on whether they were tested in the 0⁰ direction (face sheet layup of [−45/90/+45/0]S) or 90⁰ direction (face sheet layup of [+45/0/-45/90]S). The CAI strength results showed that the specimens tested in the 90⁰ direction had a 19% drop in CAI strength compared to specimens tested in the 0⁰ direction. This was attributed to the 0⁰ load bearing plies in the 0⁰ direction specimens being "tucked in" at the center of the specimen thus providing more stability against microbuckling. This raised the question as to what CAI strength would specimens tested at +22.5⁰ (face sheet layup of [−22.5/−67.5/+67.6/+22.5]S) and −22.5⁰ (face sheet layup of [−67.5/+67.5/+22.5/-22.5]S) have compared to specimens tested in the 0⁰ and 90⁰ direction. Results presented in this study show that the specimens loaded at +22.5⁰ and −22.5⁰ have a similar average CAI strength compared to the specimens loaded in the 0⁰ direction. The specimens loaded in the 90⁰ direction exhibit 16% lower average CAI strength. Additional specimens were tested in the +45⁰ direction to put the 0⁰ load bearing fibers on the outside of the specimen to see if this would decrease the strength as has been documented for undamaged strength. These specimens have average CAI strength values between the 0⁰ direction average CAI strength values and the 90⁰ direction average CAI strength values. [ABSTRACT FROM AUTHOR]

Hierarchical honeycomb is a topology presenting better weight-efficiency than the conventional honeycomb. However, the existing research are mainly conducted based on an assumption of uniform in-plane wall thickness. Rare studies consider the effect of different wall thicknesses in hierarchies. This paper investigates the out-of-plane crashworthiness of vertex hexagonal-based hierarchical honeycombs with non-uniform wall thickness in distinct hierarchies experimentally and theoretically. The coupons with parent material of 316L steel are obtained using Selective Laser Melting fabricating technique. The experimental results indicate that the first order honeycombs with uniform wall thickness experience a failure mechanism transition from local elastic buckling to local plastic buckling of cell walls at the critical density of 0.0772. A progressive folding wave can be identified when relative density is lower than 0.0386. At any edge length ratio, the plateau crushing stress increases monotonously as the increase of the wall thickness ratio, but not for the half wavelength. Both the half wavelength and maximum plateau crushing stresses are linearly related to relative density. For the first order honeycombs, the effect of edge length ratio is more considerable on the plateau crushing stress than the wall thickness ratio. The second order honeycombs exhibit higher half wavelengths and maximum plateau crushing stresses than the first order honeycombs owing to the more considerable cell wall constraint among the hierarchies. Compared to the hierarchical honeycombs with uniform wall thicknesses at relative densities of 0.005∼0.0386, the non-uniform wall thickness enhances the maximum plateau crushing stress significantly, especially at a low relative density, and the maximum improvements for first order and second order honeycombs are 71.5 and 48.6%, respectively. However, the absolute improvements are similar, averaging approximately 1.18 MPa. This work provides a foundation for developing ultralight hierarchical material candidates applied in passive protection equipment, such as aircrafts and vehicles. [ABSTRACT FROM AUTHOR]

In conventional sandwich construction, the core component is typically made of Nomex honeycomb and sandwiched between two facesheets, a lower and an upper facesheet. To enhance the load-bearing capacity of this Nomex honeycomb core sandwich (NHCS) construction, we propose a NHCS construction that is continuously encased by a composite fabric facesheet on all four sides. We experimentally and numerically examine the bending response of this encased NHCS construction through a three-point bending test. We consider and discuss the effect of the orientation of the honeycomb core component and the formation of the facesheet separately to reveal the mechanism by which the composite facesheet encasing enhances the construction. Our results demonstrate that composite facesheet encasing significantly improves the bending response of the NHCS construction, with a much greater advantage than the increase in mass compared to conventional sandwich construction. The superiority of the encased composite facesheet is significantly influenced by the orientation of the honeycomb cell and the direction of the fiber ply-stacked laminate facesheet. In addition, we compare the bending response of the encased honeycomb sandwich construction with that of competing sandwiches and show that the proposed sandwich with a continuously encased composite facesheet has a superior lightweight advantage. [ABSTRACT FROM AUTHOR]

This study presents the findings of an investigation into the effect of varying the thickness of a carbon/epoxy face sheet of a Nomex honeycomb sandwich panel on its the flexural properties. The thickness (hs) of the face sheet was varied by increasing the number of plies from one 0.25 mm thick layer to eight such layers, giving a total nominal thickness of 2.0 mm, whilst maintaining a constant thickness of the core. The flexural properties of the sandwich panels were investigated through a series of three- and four-point bending tests. A particular focus was on identifying changes in the failure mode with increasing face sheet thickness. The flexural properties of the sandwich panels were predicted using sandwich beam theory, where the deviation from the experimental values was shown to be less than 13%. A two parameter Weibull distribution model was used to predict the maximum flexural load using an analysis of variance (ANOVA) tool and an excellent level of correlation was observed with the experimental values. The difference between the predicted maximum load values and the experimental results was below 5% in all cases. A brittle mode of failure was observed in the thickest panel. The sandwich panel based on 1.5 mm thick face sheet was identified as being the most appropriate design, both in terms of strength and stiffness. [ABSTRACT FROM AUTHOR]

Detecting disbonds in honeycomb sandwich structures using ultrasonics is challenging due to the complex wave propagation. This paper investigates the method for disbond quantification in honeycomb sandwich structures using laser ultrasonics. In the experiments on an aluminum specimen, the detection frequency range was determined by the local defect resonance (LDR) in the disbond regions. The energy maps of bandpass wavefields identified the locations of disbonds. To improve the results, a frequency-wavenumber analysis of the wavefields was performed. The wavenumber spectra were reconstructed by wavenumber filtering to strengthen the outline components for quantifying disbonds. Local cross-correlation (LCC) was proposed to show the outlines of disbonds and honeycomb cells, whose results agreed well with the X-ray imaging. Moreover, LCC could also quantify a disbond in the composite honeycomb sandwich structure. Consequently, combining energy maps and LCC results can effectively detect the locations and sizes of disbonds in honeycomb sandwich structures. [ABSTRACT FROM AUTHOR]

Honeycomb cores are used extensively in different sectors of industry to build advanced lightweight structures which take advantage of high stiffness-to-weight and strength-to-weight ratios. To further increase their mechanical properties, structural hierarchy is considered already from a conceptual point of view. It is proven to be highly effective in enhancing mechanical performance in different loading scenarios but affordable realisation of practical applications remains limited. The present study focuses on the out-of-plane compressive behaviour of a novel hierarchical sandwich honeycomb core with an emphasis on compressive strength, both in virtual and in experimental testing. The finite element model is validated for through-the-thickness compressive loading by physical experiments and it can subsequently be used for further structural optimization. The paper concludes with a comparison between the proposed hierarchical structure and conventional expanded honeycombs. The performance analysis highlights the advantages of the introduction of structural hierarchy to the state-of-the art honeycomb and it shows a high potential for the use in the construction of sandwich panels and parts. [ABSTRACT FROM AUTHOR]

As for high resolution satellite application field, novel C/SiC honeycomb sandwich structure is the first to propose and develop on account of such many attractive properties as excellent ultrahigh dimensional stability in thermal and moisture coupling environment, lightweight and high load-bearing. Three types of C/SiC honeycomb sandwich structures were fabricated for the first time as opto-mechanical structure in satellite. The innovative interlayer-crosslinking method to weave the continuous carbon fiber fabric of honeycomb core was proposed. The compressive properties of novel C/SiC honeycomb sandwich structures were investigated. Meanwhile, the damage mechanism for sandwich structures were analyzed by non-destructive testing. The results showed that the innovative fabrication processing possessed the capability to prepare high quality C/SiC honeycomb, which was shown from the volume and distribution of pores in the X-ray tomography. The compression modulus and strength of the C/SiC honeycomb reached 927 MPa and 10.76 MPa, and showed better rigidity and higher strength compared with classical honeycombs. Two main types of cracks wall were found in the C/SiC honeycomb, i.e., the horizontal ones in the wall with t thickness and the inclined ones in the wall with 2 t thickness. The outstanding compressive performance was attributed to the high mechanical property of ceramic-matrix composite with fiber pull-out mechanism. The exceptional lightweight capacity was inherited from the low bulk density of honeycomb structure ranged from 0.08 g/cm3 to 0.15 g/cm3. This study can help for the development of lightweight materials for opto-mechanical structure in aerospace optical remote sensing technology. [ABSTRACT FROM AUTHOR]

A metamaterial plate with multi bandgaps is proposed for vibration suppression by integrating membrane-mass structures that can be used as locally resonant metastructure into a honeycomb sandwich structure. The finite element method is employed to calculate the band structure and the transmission spectra. The formation mechanisms of the locally resonant bandgaps are investigated via the analysis of the mode shapes of the membrane-mass resonator and face plate in a unit cell. The effects of the location of the attached mass on the bandgap property and an improved multi bandgaps structure is designed and discussed. Results show that the proposed multifunctional metamaterial exhibits an excellent vibration suppression performance, as well as a significant designability. Moreover, a specimen of the proposed metamaterial is fabricated and experimental measurements are performed, and a good agreement between the numerical predictions and the experimental results is obtained. The results of this study will be useful for the design of sandwich structures with multiple vibration bandgaps. [ABSTRACT FROM AUTHOR]

To investigate a new type of bionic energy-saving sandwich plate—the beetle elytron plate (BEP), the compressive mechanical properties of short basalt fiber reinforced epoxy resin composite BEPs and honeycomb plates with different polyvinyl chloride foam densities and height-to-thickness ratios were investigated. The mechanism of the coupling effect of the core structure, foam density and height-to-thickness ratio was revealed by observing the failure mode of the outer and inner ring honeycomb walls. This study can provide useful instruction for designing lightweight sandwich structures and accelerate the application of BEPs in engineering. [ABSTRACT FROM AUTHOR]

This study proposes a honeycomb with a sine waveform to increase the impact resistance against bird strike on the vertical stabilizer leading edge. A 2-stage comparison was made using the experimental test results in the literature to validate the model in the finite element environment. At first, the change in diameter, velocity, pressure, and scattering of particles when the bird model hits a square plate was compared with experimental data. In the second stage, an impact was made on the vertical stabilizer leading edge made of composite sandwich material. The deformation in the Z-direction occurring in the vertical stabilizer leading edge's center and the ribs' convergence were compared. The Ls-Dyna results show reasonable qualitative agreement with the experimental result. Finally, the straight walls of the honeycomb in the vertical stabilizer leading edge were modeled as a sine wave. The analyses were diversified using design parameters with different values. According to the analysis results, improvements of up to 9.79%, 28.58%, and 5.02% were observed in the deformation, the approach of the ribs, and sum of the reaction forces, respectively. These results contribute to bird strikes where strength per unit weight is essential. [ABSTRACT FROM AUTHOR]

Approach for mechanical characteristic experimental analysis of honeycomb core manufactured by fused deposition modelling is suggested. Experimental analyses of shear and tension of the honeycombs specimens fabricated from PLA and ULTEM 9085 materials are performed. The experimental studies are accompanied by the finite element simulations of the shear and the tension experiments of honeycomb core. As follows from experimental and numerical studies, both the geometrical nonlinearity and plasticity behavior of the material must be accounted for the honeycomb tension analysis. The force-displacement response of honeycomb tension has nonlinear behavior. [ABSTRACT FROM AUTHOR]

Poly (p -phenylene benzoisoxazole) (abbreviation: PBO) paper honeycomb core (PPHC) is gradually being used as a novel honeycomb material for lightweight structures in high temperature environment. However, compressive properties of PBO paper can hardly be obtained accurately due to the thin thickness and easy-to-buckling of the paper. Therefore, the Short Span Test Method is applied to obtain the compressive strength of PBO paper. The compressive strength and failure of PBO paper are characterized experimentally for the first time. The strength of compression is then used in theoretical formula to study the compressive behaviors of PPHC and the reasonable agreement with the experimental results indicates the validity of the compressive strength. Furthermore, the failure mode of PPHC subjected to compressive loads is obtained, which presents the importance of the accurate characterization on the compressive strength of PBO paper. [ABSTRACT FROM AUTHOR]

Bionic and gradient designs offer promising applications in honeycomb structures. The intersection unit of the beetle elytra is extracted as to enhance regular hexagonal honeycomb (RHH), and several bionic honeycombs are proposed. Finite element (FE) modeling approach is verified through formulae and experiments. Curves of force and displacement of bionic honeycombs present two prominent stages under medium- and low-speed impacts in plateau stage, and several bionic honeycombs exhibit a zero or negative Poisson's ratio. The specific energy absorption (SEA) of INT_6, whose crashworthiness is best in bionic honeycombs. A gradient design of INT_6 is implemented to further increase its crashworthiness. Multi-objective optimization design (MOD), which aims to simultaneously increase the SEA and reduce the peak crushing force, is adopted to determine the optimal parameters of each layer of graded INT_6. The SEA of the optimized graded INT_6 increase 142%, and its peak crushing force decrease by 25.4% compared with those of the INT_6. [ABSTRACT FROM AUTHOR]

Honeycomb materials are commonly used as cores for sandwich panels. While empirical evidence exists showing that the transverse shear strength of a honeycomb core is affected by its thickness, the accuracy of empirical guidelines and the reasons for the changes in strength are not well understood. Four-point flexural testing of sandwich beams and a detailed cellular finite element model are used to investigate transverse shear failure of Nomex™ honeycomb core material. Transverse shear strengths at varying core thicknesses were compared to manufacturer specifications and used to determine normalised strength correction factors for thickness. These factors correlated well with trends shown in previous literature, where core shear strength decreases with increasing core thickness. The failure mode investigation showed a transition between modes as core thickness increased. The thinner cores experience shear fracturing of individual cell walls followed by local cell wall buckling, intermediate thickness cores initially failed by cell wall local buckling, then fractured and larger thickness cores appeared to fail by overall cell column buckling. [ABSTRACT FROM AUTHOR]

The trapped air in unvented honeycomb core and the surrounding environment can induce a pressure differential across the facesheet during launch ascent. Combined with the presence of a defect, the pressure differential across a facesheet in combination with external loads can cause facesheet failure or unstable facesheet debond growth. While honeycomb core venting is the recommended solution, there might be practical limitations in implementing this solution or the possibility that a structure intended to be vented is partially unvented due to manufacturing issues. A methodology for accepting composite sandwich structures for space applications is presented, which heavily relies on the building block approach to characterize the facesheet strength and interfacial fracture toughness. To demonstrate the approach, an allowable flaw size is defined for a hypothetical flight condition using analyses anchored to subscale tests. [ABSTRACT FROM AUTHOR]

Disbond damage growth in honeycomb cored sandwich structures due to static and fatigue mixed mode loading is investigated numerically and experimentally. A two dimensional finite element model was generated using core homogenization and the Crack Surface Displacement Extrapolation mode separation method, integrated into a fracture mechanics based analysis sub-routine to predict face/core interface fatigue crack propagation. The Cycle Jump technique was furthermore applied to accelerate fatigue analysis. Mixed mode fatigue characterization testing was conducted using Double Cantilever Beam specimens loaded with Uneven Bending Moments, generating a relationship between crack propagation rates and energy release rate amplitudes as a modified Paris Law, measured at three mode-mixity phase angles. The measured Paris laws were subsequently used as input data for the numerical fatigue model. The numerical model was validated against CFRP/Nomex® Sandwich Tearing Test specimen tests with a propagating face/core interface crack yielding varying mode-mixities. The results from the validation showed good agreement between numerical predictions and experimental measurements. [ABSTRACT FROM AUTHOR]

As an aircraft or spacecraft ascends, the atmospheric pressure drops. If the internal pressure is not released, a pressure differential develops on the facesheet. With an in-plane load from vehicle acceleration as well, the pressure and in-plane load may cause failure. Vented sandwich structures are strongly preferred since they release the internal pressure; however, special cases still require an unvented design. This paper provides an analysis and test methodology for unvented sandwich structures. Parametric studies of facesheet-core debonding and buckling were conducted via finite element analysis, considering geometric, material, and load parameters. Design curves based on the key nondimensional parameters were tuned to the data from the parametric study, providing a tool to predict facesheet-core debond failure. Examples of how to use the design curves in practical applications are provided. [ABSTRACT FROM AUTHOR]

In this study, dynamic explicit analysis was performed to examine the air-blast performance of various hybrid sandwich designs in terms of face plate deflections and energy dissipation capacity under the conventional weapons effects program (CONWEP) air-blast loads ranging from 3 kg to 8 kg trinitrotoluene for stand-off distance ranges from 150 mm to 200 mm. The blast resistance of honeycomb sandwich configurations was evaluated using steel honeycomb with different core topologies, crushable Al foam-filled steel honeycomb, and steel or steel with 3D Kevlar/polypropylene laminate employing fiber metal laminate (FML) front face. For an accurate prediction of the deformation mechanism of all steel parts, the Johnson-Cook (J-C) model was used. The composite failure criteria of Hashin, Puck, and Matzenmiller were implemented to accurately examine the fiber and matrix damage behavior. The novel hybrid design of the honeycomb sandwich structure's blast resistance is improved by the employment of foam-filled honeycomb, an FML front face, and a circular honeycomb core. In comparison to other sandwich configurations, a novel designed hybrid sandwich construction composed of foam filled circular honeycomb with FML front facing and steel back facing (FCH-1KP0.5) achieved the highest blast resistance due to its lowest face deflection with the smallest plastic dissipation energy. [ABSTRACT FROM AUTHOR]

To develop a new type of bionic curved sandwich plate, it is necessary to first develop experimental methods and evaluation criteria for curved plates. Thus, this paper focuses on an aluminum cylindrical honeycomb plate and proposes two types of clamping methods for radial compression tests. Using finite element simulation, radial compression tests were carried out, and the mechanical characteristics under different clamping methods were studied. The results showed that (1) the two types of clamping methods have significant effects on the radial compression performance, and each has its own characteristics. The influence mechanism was explored from the perspective of the deformation shape of the sample and the sliding direction of the foot. (2) Clamping methods were given with regard to different experimental purposes or engineering application objects (backgrounds), and three clamping methods that are easy to prepare and have great universality were also presented. This research provides an important theoretical basis for the development of curved plates, radial compression test methods for curved plates and the formulation of corresponding test standards. [ABSTRACT FROM AUTHOR]

Numerical simulation along with experimental validation are used to investigate the flatwise compression behavior in the out-of-plane direction of several 3D woven honeycomb composites with varied cell geometry such as hexagonal (HX), triangular, and rectangular structures. For all the structures, the perimeter of the unit cell was kept constant. Edgewise compression and three-point bending behavior were compared experimentally for all three configurations. The flatwise compression behavior of honeycomb structures has been predicted using FEM on the LS-DYNA platform, and the results have been validated using experimental data. The predicted values are found to be in good agreement with the experimental results. Hexagonal honeycomb shows better results as compared to other cell structures as revealed by both experimental and numerical analysis. [ABSTRACT FROM AUTHOR]

This study presents experimental results of compression after impact (CAI) testing of aluminum honeycomb core sandwich structure with face sheets made of quasi-isotropic carbon/epoxy with two orthogonal directions of testing. In a previous study examining the CAI strength of honeycomb sandwich structure,1 it was found that that specimens had different CAI strengths depending on whether the core was oriented in the "L" or "W" direction. Since the face sheets were quasi-isotropic and the core should not (theoretically) affect the CAI strength for a given amount of damage (if the specimens fail by face sheet failure), this result was puzzling. In the study presented in this paper, further CAI tests, along with open hole compression testing were used in an attempt to ferret out the cause of the differing CAI strengths in the aforementioned study. The results showed that the lower CAI strength values were not due to the core orientation, but to the change in the quasi-isotropic face sheet ply sequence due to the 90° rotation. [ABSTRACT FROM AUTHOR]

Sandwich structures are frequently used in structural areas where lightness and strength are essential. These structures are indispensable for sailing boats, and ground and air vehicles. The base purpose of this study is to investigate the effect of wave parameters on the sandwich structure. The data obtained from the bending tests of the model created using Ls-Dyna was compared with the experimental data of the literature. There is a 3.05% difference between the peak force in experimental and Ls-Dyna. The force-deformation plots are coherent, and the progressive images of the sandwich structure during bending are similar. In addition, using theoretical approaches, the highest force and the amount of collapse during bending were determined. There is a difference of 3.1% between the theoretical approach and Ls-Dyna values. Thus, the Ls-Dyna model was validated. The flat cell walls of the honeycomb were modeled as a sine wave. Four wave numbers and wave amplitudes were used. In this way, 16 different analysis files were created. The results show that the new sandwich structure's specific peak force and specific energy absorption (SEA) increased by 7–110% compared to the ordinary flat walled sandwich structure. This research will assist in the design of new sandwich structures. [ABSTRACT FROM AUTHOR]

A novel hybrid composite honeycomb sandwich structure (HCHSS) and metallic honeycomb sandwich structure (MHSS) were developed to obtain realistic and blast resistance parameters for the consideration of blast loading. Hybrid composite square honeycomb sandwich structure (HCSHSS) and metallic honeycomb sandwich structure with different cores such as square, hexagonal, octagonal, and circular were modelled to obtain the target protection level (lowest deflection) for the vehicle armour structure. The Johnson-Cook and Donadon failure criteria were incorporated into finite element analysis (FEA) for MHSS and HCSHSS, respectively. For the progressive damage modelling of the HCSHSS, the Donadon criterion was implemented in ABAQUS/Explicit software as a user-defined subroutine. The HCSHSS showed the fibre failure, matrix failure and delamination modes of failure in composite laminates and the plastic deformation failure of the core and metal plates. The HCSHSS was shown to have excellent blast worthiness properties in comparison to the MHSS. The metallic circular honeycomb sandwich structure (MCHSS) was shown to have the minimum deflection of the top and bottom face plates as compared to the square, hexagonal and octagonal honeycomb sandwich structures. A novel HCSHSS has obtained the minimum deflection for both the top and the bottom face plates in comparison to the other MHSS. [ABSTRACT FROM AUTHOR]

In this paper, a novel plate lattice-filled square honeycomb (PLSH) is proposed in an attempt to improve the quasi-static compression performance and energy absorption of structure. Firstly, the quasi-static compression performance of the 3D-printed PLSH was analyzed through experimental investigation and finite element analysis. The results showed that the compressive strength and energy absorption capacity of the proposed PLSHs are higher than the sum of those of square honeycomb (SH) and plate lattices (PLs) which were tested individually. It can be seen that compressive strength per unit mass σ p / ρ and energy absorption per unit mass E M by 15%–45% and 51%–151% relative to the SH, respectively, and 65.2%–582% and 78%–196% relative to the PLs, respectively. The strengthening mechanism is that the mutual constraint between the SH and PL stabilizes the buckling and alters the compressive deformation mode of both constituents, resulting in elevating compression performance and energy absorption capability of the PLSH. [ABSTRACT FROM AUTHOR]

This study develops the governing equations and characterizes the mechanical properties of a new orthotropic accordion morphing honeycomb structure containing periodic arrays of U-type beams reinforced with glass fibers. Castigliano's second theorem is modified to develop the analytical equations to predict the deformation behavior of a single orthotropic ply under a combined axial, bending, and shear loadings. Accordingly, the elastic properties of the orthotropic structure including elastic stiffness, shear stiffness, and in-plane Poisson's ratios are calculated by the developed equations. The honeycomb structure is manufactured by 3D printing, and the samples are subjected to tensile tests to experimentally validate the analytical solutions. Multiple finite element simulations are also used to validate the results. A good agreement is observed between the analytical solution, the experiments, and simulations, confirming the robustness of the analytical solution to predict the full elastic properties of the composite cellular. The results show that the periodic arrays of U-type and vertical beams can generate low in-plane stiffness in the morphing direction and high in-plane stiffness in the transverse direction, respectively. A zero Poisson's ratio feature is achieved by employing straight beams which result in a high stiffness in the perpendicular direction. The proposed accordion cellular honeycomb structure exhibits the flexible response along the accordion shape direction, with a significant stiffness in its transverse direction. Moreover, the new orthotropic structure has considerably greater strain to failure in the morphing direction compared with a conventional isotropic configuration. These features prove that this type of structure can be applied for the aerospace morphing structures such as wings. [ABSTRACT FROM AUTHOR]

Honeycomb materials have been widely used in architecture, aerospace, and civil engineering in recent years. In this work, hexagonal hierarchical honeycombs with regular triangular substructures are studied. Based on the analytical model, expressions of the relative density and collapse stress are derived. Numerical results show that the substructure number, aspect ratio, and wall angle have different influences on the relative density. The collapse stress of hexagonal hierarchical honeycombs is sensitive to the relative density. Deformation modes of honeycomb structures depend on impact velocities, and secondary deformation is observed due to the introduction of triangular substructures. The kinetic energy and absorption energy of hexagonal hierarchical honeycombs are also provided to investigate the energy transformation and absorption. Because of the secondary deformation, hierarchical honeycombs have better energy absorption performance than conventional ones. [ABSTRACT FROM AUTHOR]

The hexagonal honeycomb core sandwich panels used in the satellite structure are subjected to severe vibration during launch. Therefore, the amounts of natural frequencies of these panels are of great importance for design engineers. Three-dimensional finite element modeling of the core considering all geometric parameters (i.e., a high-fidelity model) to achieve accurate results is not cost-effective. The honeycomb core is traditionally equivalent to a homogenized continuum core (i.e., a low-fidelity model) using simple analytical relations with ignoring the adhesive layer at the double cell-walls and radius of inclined cell-wall curvature. In this study, analytical formulations are first presented for the prediction of the equivalent elastic properties of a hexagonal aluminum honeycomb with considering all geometric parameters including adhesive layer thickness, cell-wall thickness, inclined cell-wall length, radius of inclined cell-wall curvature at the intersection, internal cell-wall angle, and honeycomb height. Then, two aluminum honeycomb core sandwich beams with free-free boundary conditions are modeled and analyzed in Abaqus finite element software, one with 3D high-fidelity core and the other with 3D low-fidelity core. In order to validate the results of the equivalent model, the modal analysis test was performed and the experimental natural frequencies were compared. The obtained results show a good agreement between the 3D low-fidelity and high-fidelity finite element models and experimental results. In addition, the influence of the above-mentioned geometric parameters has been investigated on the natural frequencies of a sandwich beam. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical properties of Nomex® paper coated with resin and composite Nomex® honeycomb sandwich structures (CNHSS) were obtained by tensile tests and flatwise tests respectively. The fundamental mechanical properties of the Nomex® paper were used as input materials parameters of finite element model generated at meso-scale level for the CNHSS, and the mechanical properties of CNHSSs were used to validate the numerical results. Based on the test and numerical results, the theoretical equations were modified to predict the flatwise compressive buckling strength and modulus of the CNHSS. The numerical and theoretical results clearly revealed that the CNHSS had two flatwise compressive elastic moduli. However, the flatwise test can only capture the second flatwise compressive elastic modulus due to manufacturing geometric defects of the cell walls. The numerical and test results showed that the manufacturing geometric defects of the cell walls showed little influence on the ultimate flatwise compressive strength. And the modified equation can predict the flatwise compressive buckling strength and modulus of the CNHSS with sufficient accuracy. [ABSTRACT FROM AUTHOR]

The use of 3D printing to produce acoustic panels with good mechanical and acoustic properties was investigated in this paper. Various fiber layups of the fiberglass face sheet and core designs were fabricated and tested for their indentation resistance and acoustic absorption performance. It was found that the bidirectional face sheet layup exhibited the best indentation energy absorption recording 4.2 J, which is 37% more than the 45-degree layout and 66% more than the quasi-isotropic layup. The specific energy absorption of the hybrid honeycomb core is the best among the three core designs recording 404 J/kg, which is 56% higher than the corrugated triangle with horizontal beam core (359 J/kg) and 20% higher than double ellipse core (335 J/kg). Computed-Tomography (CT) scan was used to study the fracture behavior of the sandwich structures. It was found that the bidirectional layup exhibited a different failure mode as compared to the 45-degree and quasi-isotropic layup. In terms of the acoustic properties, the face sheets with various layup patterns have a low acoustic absorption coefficient with minimal differences from each other at low frequencies (500 Hz–3000 Hz) and have higher absorption coefficients with greater differences from each other at frequencies between 3000 Hz–6500 Hz. The absorption curve was significantly affected by the design of the core. The orientation of the core also comes into play if the core is asymmetrical. The hybrid honeycomb sandwich structure was the optimal structure among the three designs for balanced indentation resistance and acoustic insulation. [ABSTRACT FROM AUTHOR]

The present article discusses the effect of impact damage on residual compressive strength of aluminum alloy honeycomb sandwich panel (HSP). Multiple dents were created in HSP by penetrating indenters of different diameters through quasi-static indentation technique. The damaged samples were compressed edge-wise for determination of in-plane compression after impact (CAI) strength. The failed samples were macroscopically examined to reveal the underlying damage mode. Experimental results showed that the presence of multiple dents of 5 mm size or less do not appreciably affect the CAI strength of aluminum alloy HSP. However, moderate reduction in CAI strength was observed in case of multiple dents of 10 mm. Compressive strength was reduced by 18% in presence of four dents of 10 mm diameter. The maximum reduction in CAI strength of up to 30% was observed in samples impact damaged by 15 mm indenter. Examination of failed HSP showed that the maximum load was sustained taken by aluminum facesheet whereas the contribution of honeycomb core was insignificant. Research findings exhibit that the CAI strength of aluminum alloy honeycomb structure is not sensitive to impact damages size less than 5 mm diameter however dents above 5 mm size can seriously impair mechanical performance and structural integrity. [ABSTRACT FROM AUTHOR]

The equivalent in-plane elastic modulus (E y S) of a honeycomb sandwich in the direction of cell vertical wall can be assessed by the law of mixture from the modulus of face sheet (E p) and the equivalent modulus of honeycomb core (E y C). However, significant errors as large as 40% can be made depending on material and geometry parameters, when the used E y C is obtained from a cellular model of core alone without considering the skin effect of face sheet. The main reason of the error is that the rigidity to deformation of y -direction is different greatly between the vertical cell wall of core and inclined cell wall of core. In the present paper, an analytical model is proposed to assess E y S of honeycomb sandwich with considering the interference effect of the core with the face sheet. In the proposed model, the influence of the face sheet rigidity on E y S is taken into account. The results demonstrate that the contribution of the core to E y S is also dependent on the face sheet rigidity significantly. The validity of presented model is verified by comparing the results with numerical results of FEA. [ABSTRACT FROM AUTHOR]

The paper composite sandwich structure with corrugation and honeycomb cores has been widely used in civil and national defense industries, and the cushioning energy absorption characteristic is a key indicator to evaluate the performance of this composite structure. Therefore, this paper is focused on the influences of honeycomb thickness on the shock acceleration response and deformation characteristics to analyze cushioning energy absorption performance of the composite structure by various experimental tests. The experimental result shows that the paper corrugation layer firstly comes into crushed, and then the paper honeycomb layer is crushed. Additionally, the large honeycomb thickness may cause the secondary collapse of paper honeycomb layer. Under the same impact energy or impact mass, the cushioning energy absorption of the single-sided composite sandwich structure is better than that of the double-sided structure with the same honeycomb thickness. However, the impact resistance of the double-sided composite structure is better than that of the single-sided structure. For the paper composite sandwich structures with the honeycomb thicknesses 10, 15, 20, and 25 mm, the increase of honeycomb thickness would decrease the cushioning energy absorption of the whole structure under the drop impact with low energy. However, under the drop impact with high energy, the influence of honeycomb thickness on cushioning energy absorption is contrary. For the paper composite sandwich structure, the specific energy absorption, unit volume energy absorption, and stroke efficiency for the honeycomb thicknesses 10, 15, 20, and 25 mm are higher than those for the honeycomb thickness 70 mm. Therefore, the low honeycomb thickness is more advantageous for the cushioning energy absorption of paper composite sandwich structure. [ABSTRACT FROM AUTHOR]

A novel angle graded auxetic honeycomb (AGAH) core is designed for sandwich structures in the present study. The angle of the cells is varied through the thickness of the AGAH core using linear functions. Therefore, the thickness of the cell walls is kept constant along the gradation of the cell angle, and the length of the cell walls is changed through the core thickness as the result of angle variation. New analytical relations are proposed to predict the equivalent elastic properties of the AGAH core. The performance of the new proposed core is analytically assessed for the vibrational behavior of a sandwich plate. The governing equations are deduced adopting Hamilton's principle under the assumption of quasi-3D exponential plate theory. Three-dimensional finite element (3D-FE) simulation is accomplished to verify the analytical results of the vibrational response of the sandwich structure. The influence of variation of the cell wall, the cell angle and cell aspect ratio of AGAH core, and geometric parameters of the sandwich structure are investigated on the vibration response of the sandwich panel. The present graded design of the auxetic honeycomb enhances the specific stiffness (i.e., stiffness to density ratio) and consequently increases the natural frequencies of sandwich structures with this type of core. [ABSTRACT FROM AUTHOR]

In this study, the compression mechanical response of tandem honeycomb cores was investigated to determine the effect of dislocation length and layer height on the compression resistance of tandem honeycomb. A series of flatwise compressive tests were carried out on single-layer and double-layer honeycombs, which showed that tandem honeycomb obtains higher equivalent elastic modulus and collapse stress, and the core assembled with dislocation can achieve almost the same collapse stress with the aligned assembled honeycombs. In addition, a mesoscale finite element modeling method was developed and used to evaluate the effect of dislocation length and layer height on the mechanical response of tandem honeycomb through parametric simulation. Overall, our results suggest that dislocation length is proportional to the collapse stress, and the layer height decides the equivalent modulus and collapse stress of tandem honeycomb, specifically, dislocation length helps achieve higher collapse stress in the tandem honeycomb of varying layer heights. [ABSTRACT FROM AUTHOR]

This research presents a numerical study on vibro-acoustic and sound transmission loss behavior of an aluminum honeycomb core sandwich panel with fabric-reinforced graphite (FRG) composite face sheets. The sandwich theory, which assumes the honeycomb core as an orthotropic structural layer, is applied to investigate the free and forced vibration behavior of the panel. The radiated sound power from the panel is quantified by Rayleigh integral method, and the random diffuse field as an incident sound source is derived based on finite element method with the employment of ACTRAN. A validation between the simulated results and the experimental data published is carried out to demonstrate the accuracy and reliability of the present approach. The comparison between different materials of honeycomb sandwich structures illustrates the advantages of the fabric-reinforced graphite honeycomb sandwich structure over the other types of sandwich structures considered. The effects of different boundary conditions and honeycomb structural geometry properties on the acoustical performance of the stiffness of the FRG panel are also investigated. The approach of the present research provides useful guidance for evaluating and selecting the other honeycomb sandwich panels when the vibratory and acoustic behaviors of the panels are considered. [ABSTRACT FROM AUTHOR]

Hybridization of sandwich panels and their different components have drawn huge attention due to the significant improvement in their attributes. Hybrid core of 'Polyester Pin-reinforced Foam filled Honeycomb Sandwich panels' (PFHS) were fabricated and compared with unreinforced 'Foam filled Honeycomb Sandwich panels' (FHS) in terms of low velocity impact and Compression After Impact (CAI) performance. The impact damage area was calculated by employing MATLAB image processing technique. Incorporating through thickness pins for connecting faces and core is an effectual way to improve interfacial bonding, specific bending stiffness and also imparts out of plane properties for sandwich panels. The low velocity impact tests performed on the sandwich panels revealed that the polyester pin reinforcement in foam filled honeycomb sandwich panel improved the load bearing capacity, total absorbed energy and reduced the impact damage area significantly. In CAI test, debond, wrinkling of face sheet, and buckling of face sheet and core are the major modes of failure. The addition of the pins enhanced the compressive strength for all the impact energy levels. [ABSTRACT FROM AUTHOR]

This paper reports on the production and evaluation of a new class of "Z-axis" composite sandwich panel where the core consists of a dense array of vertically-aligned, 3 mm long E-glass fibre composite "beams". The E-glass fibre bundles were aligned using electrostatic charging. A procedure was developed to retain the orientation of the short-fibre bundles whilst they were impregnated and cured with an epoxy/amine resin system. The skins were manufactured from 4-ply carbon/epoxy prepregs with a layup sequence of (0,90)s. The out-of-plane compressive strength of these Z-axis composites was found to be 25.2 and 15.2 times greater than equivalent sandwich panels made with Nomex® and aluminium honeycomb cores respectively. Their compressive strength was found to increase in proportion to the density of the core. Buckling and fracture of the vertically-aligned Z-axis composite were the predominant failure modes observed. The shear and flexural properties of the Z-axis composites were comparable to equivalent honeycomb sandwich panels manufactured from Nomex® and aluminium honeycomb cores. [ABSTRACT FROM AUTHOR]

A theoretical model is developed to study the superior sound absorption performance of ultralight mirco-perforated sandwich panels with double-layer hierarchical honeycomb core. Numerical simulations are performed to validate theoretical model predictions and explore physical mechanisms underlying the sound absorption. Systematic parametric study is implemented to investigate the influence of specific structural parameters on sound absorption. To maximize sound absorption, optimal structural parameters of the hierarchical sandwich are obtained using the method of simulated annealing. It is demonstrated that viscous dissipation of the air inside micro-perforations and around inlet/outlet regions dominates sound absorption. Compared to micro-perforated sandwich panels with regular honeycomb core, not only the proposed hierarchical construction has much improved load-bearing capacity, but also significantly enhanced sound absorption covers a wide range of frequency. [ABSTRACT FROM AUTHOR]

This research presents the adaptation of an anisotropic hyperelastic constitutive model for predicting the experimentally observed in-plane, orthotropic, bi-modular and nonlinear-elastic responses of a commercial adhesively bonded HRP-C fiberglass/phenolic hexagonal honeycomb core. The hyperelastic constitutive model is evaluated under simple states of loading using single-element finite element analysis. The predictions of the model, including stress-strain behavior, Poisson effects, and strain energy densities, are compared with test data for the in-plane uniaxial tension/compression responses of the honeycomb core as well as the single-element model with a linear orthotropic constitutive model to highlight the effectiveness of the hyperelastic model at high strain levels. Good agreement is observed between the model predictions and test data. Tension tests in ribbon and transverse directions with the full-scale honeycomb core are also simulated to ensure the suitability of the single element model for simulations of the simple loading cases and preliminary validation process. [ABSTRACT FROM AUTHOR]

The effect of extreme cold temperatures on the quasi-static indentation and the low velocity impact behavior of woven carbon/epoxy composite sandwich panels with Nomex honeycomb core was investigated. Impact tests were performed at room temperature, –70°C, and –150°C. Two sizes of hemispherical impactor were used combined to three different impactor masses. All the impact tests were performed at the same initial impact velocity. The effect of temperature on the impact behavior is investigated by studying the load history, load-displacement curves and transmitted energy as a function of time curves. Impact damage induced at various temperatures was studied using different non-destructive and destructive techniques. Globally, more damages are induced with impact temperature decreasing. The results also show that the effect of temperature on the impact behavior is function of the impactor size. [ABSTRACT FROM AUTHOR]