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The gradient honeycomb structures absorb a wide range of energy, but a systematic study on anisotropic design is lagged. The same justify the novelty of the current work, wherein the honeycomb design of anisotropic gradient honeycomb structure comprises its originality. The gradient 3D-printed honeycomb structures fabricated samples were subjected to a static and cyclic compression test in the in-plane direction, and the energy absorption capabilities were analyzed. The cyclic compression and free vibration test confirmed the highest damping ability attributed to hybrid gradient structure. A high damping ability demonstrates application possibilities as an efficient and effective energy absorption element and other technical curiosity. [ABSTRACT FROM AUTHOR]

Featured Application: Authors are encouraged to provide a concise description of the specific application or a potential application of the work. This section is not mandatory. This study experimentally investigated the flexural fatigue behaviors of honeycomb sandwich composites subjected to low velocity impact damage by considering the type and thickness of the face sheet material, the cell size and the core height parameters. Carbon-fiber reinforced composite and the aluminum alloy was used as the face sheet material. First, the static strength of undamaged and damaged specimens was determined by three-point bending loads. Secondly, the fatigue behaviors of the damaged and undamaged specimens were determined. Low velocity impact damage decreased the flexural strength and fatigue lives but increased the damping ratio for all specimens. Maximum damping ratio values were observed on specimens with a aluminum face sheet. [ABSTRACT FROM AUTHOR]

In recent years the use of Additive Manufacturing (AM) has become increasingly widespread with numerous industries now moving towards large scale manufacture of structurally integral components. The nature of AM offers the ability to manufacture more complex and optimised geometries, such as cooling channels and honeycomb structures, which would not be possible or economically viable to manufacture using more traditional fabrication processes. However, the layer by layer build structure of AM components also introduces a complex and component specific microstructure arising from the rapid cooling rates resulting from the build parameters and geometries, which hence influence the mechanical properties. Therefore, the use of conventional mechanical test approaches to assess the performance of these materials can be limited. This paper will extend upon some of the recent research at Swansea University in applying the innovative small punch fatigue (SPF) experiment to characterise the mechanical performance of AM materials and how they compare to traditionally manufactured variants of the same alloys. Results show excellent agreement with the microstructural morphologies of the different materials, with supporting fractography evidencing the contrasting failure modes. [ABSTRACT FROM AUTHOR]

Abstract Static and fatigue behaviors of Nomex honeycomb sandwich structures were characterized by compression and bending experiments. And the finite elemental numerical simulation research was carried out based on the test data. The load level for fatigue test was determined and the necessary stiffness information for the construction of finite element model was provided by the study of static load performance. The fatigue failure mode and damage mechanism of Nomex honeycomb sandwich structures were analyzed by comparing the fatigue life curves and experimental phenomena of bending fatigue and compression tests. This study presented a method to predict the fatigue life of honeycomb sandwich structures and its feasibility was verified by experiments. [ABSTRACT FROM AUTHOR]

This paper aims to analyze the fatigue response of PLA parts manufactured through fused filament fabrication (FFF). The influence of four factors (layer height, fill density, nozzle diameter and velocity) on the fatigue performance of cylindrical specimens is studied through an L27 Taguchi experimental design. This design is run for two different infills: linear and honeycomb. Specimens have been tested on a rotating fatigue bending machine. The optimal set of parameters and levels resulting in the highest number of cycles to failure have been determined, and implemented to manufacture a second set of specimens, which have been tested at different stress levels to represent the Wöhler curve. Fill density proves to be the most influential parameter on fatigue life, followed by layer height. The tests undertaken to represent the Wöhler curve revealed that 35.8 MPa can be considered as a lower threshold of the endurance limit for this kind of specimens. This value can be useful to use these devices to manufacture human implants, as PLA is a biocompatible material. The main novelty of this paper is that no previous fatigue life assessment of PLA parts manufactured through FFF has been developed. [ABSTRACT FROM AUTHOR]

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In comparison to their weight, honeycomb composite structures have a high bending stiffness, which makes them very suited for every application such as airplanes, railway-cars and vehicles, where little weight is important. The sandwich panels consist of two thin and stiff aluminum face sheets, which are bonded to a thick and lightweight aluminum honeycomb core. These structures are subjected to dynamic loading. However, in the literature, there are hardly any fatigue properties of the honeycomb core described. The fatigue properties of the core are investigated using the finite element method and experiments. Depending on the load application, the honeycomb core fails either through core indentation or shear failure. For a fatigue prediction, both failure modes have to be investigated. Additionally, the physical behavior of the honeycomb core is depending on the orientation of the core. Hence, fatigue tests were conducted in three directions of the core: the stiffest direction, the most compliant direction and the direction with the highest stresses. A three-point bending test setup was built to study the fatigue properties of the honeycomb core. Several fatigue tests were carried out with a load ratio of R = 0.1 (maximum load 10 times bigger than minimum load) and the fatigue diagrams being illustrated. Additionally, food-cart roller tests (wheels of a cart rolling in a circle on a floor panel) were done to dynamically test the panels in every angle. The sandwich structures were modeled with the ANSYS finite element software. The simulations, which were used to determine the stress amplitudes in the specimens, are described later. In addition, buckling analyses were used to examine core indentation failure. Based on these simulations, failure predictions can be made. The fatigue life of the examined specimens is successfully approximated in this manuscript, with the lifetime analysis being based on the FKM guideline (error less than 14% in load amplitude). [ABSTRACT FROM PUBLISHER]

Abstract: Composite Sandwich Materials are being increasingly used in high-performance structural applications because of their high stiffness and low weight characteristics. Presently, the long-term performance of such structures, especially under fatigue loading, is not enough studied. The aim of this paper is to address such fatigue behaviour by using a fatigue model verified by experimentation. The fatigue model is based on the fatigue modulus concept (degradation of stiffness) which is proposed for core-dominated behaviour and for two directions cells (L and W). Two non-linear cumulative damage models (L and W) derived from the chosen stiffness degradation equation, are examined in context with the linear Miner’s damage summation and compared with available experimental results. [Copyright &y& Elsevier]

A prediction method for the fatigue life of polymer composites under arbitrary frequency, load ratio and temperature was extended to that of polymer composite structures. The three-point bending tests for honeycomb cored sandwich (SW) panels with GFRP skin plates and Nomex honeycomb core under constant strain rates (CSR) and fatigue loading at various strain rates and temperatures were conducted. The maximum bending moments for CSR and fatigue loadings strongly depend on time and temperature, and the time-temperature superposition principle for the storage modulus of matrix resin holds for the maximum bending moments for fatigue loading as well as CSR loading. The long term fatigue strength at any time, temperature and number of cycles to failure can be predicted using the master curves of the bending moment by fatigue loading based on the accelerated testing methodology. [ABSTRACT FROM AUTHOR]

Abstract: Three types of aluminum honeycomb sandwich beam specimens with different face sheet thicknesses were employed in the four-point bending fatigue tests to study the effect of face sheet thickness on the fatigue strength. The experimental results show that under the same applied bending loads, no evident relationships exist between the face sheet thickness and the fatigue life of the studied specimens. The main failure mode of the studied specimens is the debonding at the interface between the adhesive and the face sheet based on the observations during the tests. To correlate with the scattering fatigue life data of the studied specimens with different face sheet thicknesses by using the local approaches, three parameters based on the finite element simulated interfacial stresses were proposed herein. The sub-modeling technique was applied in the finite element simulations to determine the local interfacial stresses. The employed local parameters in the study were the interfacial peeling stress, the in-plane interfacial shear stress, and the linear combination of interfacial peeling and shear stress. The comparison of the correlation performance between these employed parameters was made in the study. Furthermore, the nodes with the maximum value of prediction parameters were considered as the potential locations where the debonding failure initiated. The predicted locations of debonding initiation obtained using the three parameters were also compared with the observed ones. The analytical results show that the linearly combined peeling and shear stress parameter yields better fatigue-life correlation and failure-location prediction results than the other two parameters. [Copyright &y& Elsevier]

Abstract: The effect of the amount of adhesive for bonding face sheets and cores on the bending fatigue strength of aluminum honeycomb sandwich beams was analyzed. It was experimentally proved that the fatigue strength increases as increasing the amount of adhesive. Furthermore, the applied loading parameter is not correlated with the fatigue life data of all studied specimens with various amounts of adhesive because the global parameter has no clear physical meanings with respect to the failure mechanism. From the observations made during fatigue testing, debonding at the interface between the honeycomb core and face sheet is the main cause of fatigue failure. Finite element analyses were conducted to obtain the local stress states at the interface, and these simulated stresses were employed in fatigue life prediction parameters. Three local interfacial parameters were adopted and correlated with the experimental data for the studied specimens. The predicted failure locations using the three interfacial parameters were also examined by comparing the observation results in fatigue tests. Among the three studied interfacial parameters, the combined interfacial peeling and shear stress parameter is recommended for use in fatigue design as it provides good fatigue life correlations and predicts the correct locations of failure initiation simultaneously. [Copyright &y& Elsevier]

Abstract: This study analyzed the four-point bending fatigue strengths of aluminum honeycomb sandwich beams with cores of various relative densities. The debonding of the adhesive between the face sheet and the core was identified to be the major failure mode. Several global parameters and local parameters were considered to evaluate the fatigue life of the studied sandwich structures. The finite element approach was utilized to determine the local stress/strain by considering the geometry and dimensions of the adhesive. The circular-shaped local parameter which combines the peeling stress and the shear stress of the adhesive on the debonding plane, correlates with the fatigue life of the sandwich beams with various core densities effectively. The predicted locations of debonding initiation using the circular-shaped combined interfacial stress parameter are identical to those observed in fatigue tests. [Copyright &y& Elsevier]

The article presents abstracts of current literature relating to shock and vibration. They include "Active control of noise from a vacuum cleaner," "Hermetically sealed oil-free turbocompressor technology," and "Near field acoustic holography (NAH) theory for cyclostationary sound field and its application."

This article is intended to be a tutorial on the subject of fatigue of foam and honeycomb core composite sandwich structures. First, several different analytical models for predicting the fatigue life of sandwich composites are presented. Then representative publications which have reported on the major failure modes in sandwich beams under dynamic fatigue loading are summarized, along with several related publications dealing with static and impact loading. Papers dealing with the effects of loading frequency, environmental factors, and block loading on the fatigue life of sandwich composites are discussed. Finally, recent research on different types of non-destruction evaluation (NDE) techniques employed for failure investigations during fatigue testing of sandwich structures is reviewed. Conclusions and generalizations that can be drawn from the literature are presented along with discussions of areas in which further research is needed. [ABSTRACT FROM AUTHOR]

• A theoretical model for service life analysis of auxetic honeycomb/substrate structures under thermal cycling is developed. • The auxetic structures have lower stress concentration than non-auxetic structures of the same density. • Lower relative density can increase the service life of the structures. • Auxetic structures possess much higher service life than non- auxetic structures. This paper studies the fatigue behavior of auxetic honeycomb layer/substrate structures due to interfacial delamination damage. First, the interfacial thermal stress and cyclic interfacial thermal stress intensity factor (ITSIF) at the free ends of the structure are determined in terms of the thermal shock time, relative density, aspect ratio, and internal cell angle of the honeycomb. Then, a theoretical model for the service life analysis of the structures is established based on Paris's law. The results show that the auxetic structures have a lower ITSIF level and a longer service life compared with those of the non-auxetic structures. Another interesting finding is that a reduction in the relative density of the honeycomb layer will increase the service life of the structures. This confirms the significance of applying auxetic materials in re-usable structures for thermal protection purposes. This research is the first attempt to evaluate the service life of the auxetic honeycomb layer/substrate structures under thermal cycling. [Display omitted] [ABSTRACT FROM AUTHOR]

Aluminium honeycomb sandwich panels are an interesting lightweight structural solution for several applications such as marine structures, aerospace, automotive and aeronautics. In many of these applications, in-service conditions produce fatigue loadings: as a result, safer use of aluminium honeycomb sandwich structures requires a deep knowledge of their fatigue response, which was seldom studied in previous literature. The aim of the current study is to evaluate the fatigue response of aluminium honeycomb sandwich panels subjected to three-point bending loading conditions. The experimental investigation was performed on a commercial aluminium honeycomb sandwich structure with an overall thickness of 11 mm. A preliminary static analysis was performed both under three and four point bending conditions. The static tests allowed the identification of the static bending strength and the absence of a significant strain rate influence. Crashworthiness parameters were evaluated and a slight better performance was found under four point bending. The combination of static tests with Computed Tomography analysis resulted in the observation of the phenomena involved in static bending response of aluminium honeycomb sandwich structures, which are mainly dependent on cell walls buckling. Fatigue tests were conducted under three-point bending conditions. The influence of boundary conditions on fatigue life and on collapse modes were investigated by considering different supports spans. For one condition the S-N curve was obtained and its equation was compared to literature results. Two different collapse mechanisms were observed depending on the supports span: for larger supports span a fracture of the tensioned skin was observed, whereas lower supports span produced core shear. The former mode differed significantly from static failure with the same boundary conditions. In both cases, failure occurred suddenly and this should be taken into consideration in industrial applications. An analytical model was applied to predict fatigue collapse modes and limit loads. A fatigue failure map describing the relationship between supports span, collapse modes and fatigue limit loads was obtained, in order to provide a quantitative tool for aluminium honeycomb sandwich structures design. The fatigue failure map was able to accurately predict the experimental results. • Fatigue bending response of aluminium honeycomb sandwich structures. • Collapse modes variation with boundary conditions under fatigue bending. • Effect of boundary conditions on fatigue response. • Analysis of the failure mechanisms by means of 3D Computed Tomography. • Prediction model for fatigue collapse modes. [ABSTRACT FROM AUTHOR]