Foam-filled Panels Research Articles

Experimental crashworthiness analysis of corrugated-core sandwich panels under impact loading

ABSTRACT This research scrutinizes and contrasts the crashworthiness of single-core and two-core corrugated sandwich panels with varying configurations, influenced by crucial parameters like thickness, core angle, and foam filling. Experimental investigations encompass quasi-static compressive loads and low-velocity impact tests on these sandwich structures. Employing the design of the experiment (DOE) method, the study examines parameter impacts on initial peak crushing force (IPCF) and specific energy absorption (SEA) across three sequential steps. The fabrication phase involves creating square and trapezoidal aluminium sandwich panels bonded using specialized aluminium glue. The results notably highlight the pivotal role of corrugated sandwich panel thickness in enhancing crashworthiness, displaying a direct correlation between thickness and responses. Particularly, two-core configurations exhibit superior performance in reducing IPCF during low-velocity loading compared to other panels. These structures showcase exceptional capability in diminishing IPCF rates during low-velocity loading, surpassing even foam-filled panels and demonstrating superior crashworthiness among the tested configurations.

Experimental investigation of sandwich panels using foam filled corrugated cores

Sandwich panels are commonly based on honeycomb core, which provides lightweight, high strength applications such as aero plane fuselage. These panels having metallic corrugated cores have distinctly different attributes from those having corrugated foam core. Corrugated core provides high specific stiffness and strength, whereas metallic core provides superior energy absorption. Foam corrugated core was fabricated according to ASTM standards C393M-11 with the length of 265 mm and span of 170 mm and analytical tests were made for flexural Strength and Compressive Strength for three different core types, and the results were compared with each other. In the end, compared results showed better potential in foam-filled panels than other core types.

Quasi-static and impact behaviour of foam-filled graded auxetic panel

Cellular structures (in general) and auxetic topologies (in particular) have excellent energy-dissipation characteristics and can be used as lightweight impact-energy absorbers. This paper aims to experimentally and computationally examine the behaviour of novel re-entrant auxetic graded aluminium panels filled with polyurethane foam in an auxetic pattern. The performance is compared with 3 non-graded, 1 graded and 2 foam-filled graded panels. The 6 compared auxetic panels share the same basic geometry but vary in the sheet thickness and the addition of polyurethane foam. The auxetic panels were built by corrugating and gluing 12 aluminium sheets. The material properties of the used aluminium sheets and foam were determined with standard mechanical testing. Detailed quasi-static and dynamic drop tests were conducted and compared with a non-linear computational model. The stress-strain relationships, deformation patterns, specific energy absorption, crash force efficiency and Poisson's ratio were comprehensively evaluated. Foam-filled panels revealed higher specific energy absorption and more stable deformation than non-filled panels. The developed computational models successfully describe mechanical and deformation behaviour and can be used for future virtual testing of other configurations.

Effects of Aluminum Foam Filling on Compressive Strength and Energy Absorption of Metallic Y-Shape Cored Sandwich Panel

The design of lightweight sandwich structures with high specific strength and energy absorption capability is valuable for weight sensitive applications. A novel all-metallic foam-filled Y-shape cored sandwich panel was designed and fabricated by using aluminum foam as filling material to prevent core member buckling. Experimental and numerical investigation of out-of-plane compressive loading was carried out on aluminum foam-filled Y-shape sandwich panels to study their compressive properties as well as on empty panels for comparison. The results show that due to aluminum foam filling, the specific structural stiffness, strength, and energy absorption of the Y-shape cored sandwich panel increased noticeably. For the foam-filled panel, aluminum foam can supply sufficient lateral support to the corrugated core and vertical leg of the Y-shaped core and causes a much more complicated deformation mode, which cannot occur in the empty panel. The complicated deformation mode leads to an obvious coupling effect, with the stress–strain curve of the foam-filled panel much higher than those of the empty panel and aluminum foam, which were tested separately. Metallic foam filling is an effective method to increase the specific strength and energy absorption of sandwich structures with lattice cores, making it competitive in load carrying and energy absorption applications.

The mechanical behaviour of spherical egg-box sandwich structures

Abstract This paper presents a study on the mechanical properties of spherical egg-box core sandwich panels subjected to compression. Initial attention focuses on the effect that constraining the core, via the introduction of skins, and increasing the thickness of the cell walls has on the compressive properties of GFRP and CFRP structures. Tests were also undertaken on foam-filled samples in order to investigate the influence of additional support on the crushing behaviour of the cores. Low velocity impact tests were subsequently undertaken in order to investigate the rate-sensitivity of these core structures. Finally, blast tests were conducted on the core materials to investigate their response at high strain rates. It has been shown that constraining the lateral movement of the cores, by bonding composite skins to the upper and lower surfaces, serves to enhance the mechanical properties of the core in compression. In addition, quasi-static compression testing has shown that the compressive strength of the core increases rapidly with increasing cell wall thickness, with effects being more pronounced in the GFRP structures. Tests on foam-filled panels have shown that adding a low density filler to the core serves to enhance the energy-absorbing properties of the GFRP systems. Subsequent tests at dynamic rates of loading have shown that the values of energy absorption were slightly higher than those measured at quasi-static rates, due to rate effects in the failure processes within the composite material. Finally, it has been shown that when subjected to blast loading, extensive crushing of the spherical egg-box was observed, indicating that these structures are capable of absorbing significant energy under this extreme loading condition.

An experimental study on the lateral pressure in foam-filled wall panels with pneumatic formwork

Applications of structural wall panels using flexible formwork systems have recently attracted the attention of architects and engineers. Many of such panelised systems in the market are foam-filled walls, mainly presented in the form of sandwich panels. Knowledge of cast-in-situ induced lateral pressure on the formwork is critical for the economical and safe design of flexible formwork for construction. Formwork cost, on the other hand, comprises a high proportion of the total cost of a building constructed by cast-in-situ materials. Although extensive research has been conducted on the lateral pressure of concrete formwork, the components and mechanics of the lateral pressure in foam-filled walls have not been thoroughly understood. This paper will investigate the lateral deformation, and then lateral pressure on flexible fabric formwork used for construction of polyurethane foam-filled panels. From the lateral pressure on the formwork, the tension forces in the ties are calculated by measuring the compressive force developed between the formwork edges. The results are used for design of intermediate ties for controlling the lateral deformations in an innovative foam filled panelised system, which has been designed for rapid assembly of semi-permanent buildings for post disaster housing.

Effects of aluminum foam filling on the low-velocity impact response of sandwich panels with corrugated cores

In this study, a closed-cell aluminum foam was filled into the interspaces of a sandwich panel with corrugated cores to form a composite structure. The novel structure is expected to have enhanced foam-filled cores with high specific strength and energy absorption capacity. An out-of-plane compressive load under low-velocity impact was experimentally and numerically carried out on both the empty and foam-filled sandwich panels as well as on the aluminum foam. It is found that the empty corrugated sandwich panel has poor energy absorption capacity due to the core member buckling compared to that of the aluminum foam. However, by the filling of the aluminum foam, the impact load resistance of the corrugated panel was increased dramatically. The loading-time response of the foam-filled panel performs a plateau region like the aluminum foam, which has been proved to be an excellent energy absorption material. Numerical results demonstrated that the aluminum foam filling can decrease the corrugated core member defects sensitivity and increase its stability dramatically. The plastic energy dissipation of the core member for the foam-filled panel is much higher than that of the empty one due to the reduced buckling wavelength caused by the aluminum foam filling.

Experimental study on the dynamic response of foam-filled corrugated core sandwich panels subjected to air blast loading

Abstract Effective approaches to enhance the blast resistance of sandwich structures with corrugated cores were developed by adopting three different strategies to fill the spaces within cores with polymeric foam. The baseline unfilled panels and foam-filled panels were designed and fabricated, and finally subjected to air blast loading generated by detonating cylindrical explosive. Deformation modes and failure mechanisms of tested panels were investigated. Experimental results demonstrated that the panels with back side filling strategy did not show better blast performance compared with the unfilled panels, even though extra weight was expended due to the addition of foam fillers. The panels with front side filling and fully filling strategies encouragingly appeared to possess desirable blast resistance to prevent severe fracture under high intensity blast loading. This benefit should be attributed to the sufficient crushing deformation of foam fillers and the enhanced buckling resistance of core webs. In addition, a preliminary study has been conducted to investigate the effects of front face thickness on the blast performance of foam-filled panel. Attempts of allocating component mass and filling different material have been made to explore the potential of performance improvement.

Compressive strength and energy absorption of sandwich panels with aluminum foam-filled corrugated cores

Abstract All-metallic corrugate core sandwich panels as primary loading structures may rapidly soften under compressive loading due mainly to core member buckling once the peak compressive stress is reached, resulting in reduced load-carrying capability. Inserting close-celled aluminum foam into the corrugate core has been envisioned as a feasible way to enhance the load capacity. The enhancement due to foam filling were firstly explored experimentally under quasi-static out-of-plane compression and the underlying mechanisms subsequently numerically studied using finite element simulations. The foam filled corrugated panel was found to have strength and energy absorption much greater than the sum of those of an empty corrugated sandwich panel and the aluminum foam alone. It was demonstrated that the core members in the foam-filled panel were considerably stabilized by the filling foam against lateral deflection. In particular, the elastoplastic buckling wavelength of the core members was significantly reduced and the transition from axial deformation to bending of the core member was much delayed, both of which contributing to the enhanced strength and energy adsorption capability of the foam filled panel.

An experimental investigation on the effect of strain rate on the behaviour of bare and foam-filled aluminium honeycombs

The effects of strain rate (in low-strain rate regime) on the compressive mechanical behaviour of bare and foam-filled honeycomb structures are experimentally investigated in this paper. Empirical tests show that unlike the existing theoretical formula for bare hexagonal honeycombs, the mean crushing strength of these structures is highly dependent on the strain rate, as an increase of the strain rate yields an increase in the mean crushing strength of up to 40% in some specimens. This effect would be less considerable when it comes to the case of foam-filled panels. The results also indicate that the strain rate has no effect on the densification strain but could change the plane of deformation and increase the number of folds, and consequently decrease their wavelengths.

BUCKLING OF A PLATE ON A PASTERNAK FOUNDATION UNDER UNIFORM IN-PLANE BENDING LOADS

In-plane bending loads occur in many thin-walled structures, including web core sandwich panels (foam-filled panels with interior webs) under transverse loading. The design of such structures is limited in part by local buckling of the thin webs and the subsequent impact on stiffness and strength. However, the core material can have a significant impact on web buckling strength and thus must be considered in design. This paper presents solutions for the buckling strength of simply supported plates under in-plane bending loads. The location of the neutral bending axis is allowed to vary and is characterized by a load parameter. A Pasternak model is used to account for the resistance of the foundation to compression and shear. Using the principle of minimum potential energy, buckling solutions are developed for infinitely long plates and representative foundation materials. The solutions match known results for two special cases: Uniform loading with variable foundation, and bending loads with no foundation. An order of magnitude increase in buckling strength is possible, depending on loading and foundation stiffness. The results suggest an important avenue for future development of lightweight structures, including sandwich panels and structures such as plate girders that are not typically associated with the use of foam filling.

Experiments on Shear and Buckling in Foam-Filled Panels

Experiments on Shear and Buckling in Foam-Filled Panels

Thermal Warp of Composite Panels

Warping due to temperature can be a problem with foam-filled panels since the faces may be held at widely different tem peratures and the faces are not free to ex pand or contract relative to one another. Ex pressions for estimating the warp of such structures have been derived and are com pared to experimental results. Deflections due to thermal warp and simulated wind loads are compared. The warp of panels with thin, flat faces is apparently a function solely of the relative expansion or contraction of the faces, the span, and the thickness of the panel. The stiffness of the faces and the core are important in warp only when at least one face is thick or formed (has an appreciable moment of inertia). Such faces can reduce warp, primarily by inducing shear deforma tion of the core. When they are used in com bination with cores of relatively high shear modulus, little reduction in warp should be expected. While cores of low shear modulus are helpful in thermal warp, they are harm ful to deflection under loads. Formed or thick faces are helpful in both cases.