Low-density Polyurethane Foam Research Articles

Circular Reprocessing of Thermoset Polyurethane Foams.

Thermoset polyurethane (PU) foams are widely used in industrial applications, but they cannot be recycled by conventional melt reprocessing because of their cross-linked structures. The introduction of carbamate exchange catalysts converts thermoset PU into covalent adaptable networks (CANs), which are amenable to reprocessing at elevated temperatures. However, this approach has produced solid PU films, which have fewer uses and lower commercial demand. In this work, simultaneous reprocessing and refoaming of thermoset PU foams is demonstrated by leveraging the melt-processability of PU CANs and allowing cell growth by gas generation in a twin-screw extruder. The optimal operating temperature of the refoaming process is determined through chemical, thermal, and structural analysis of PU foam extrudates. The foam-to-foam extrusion process produces controllable, continuous, and uniform foam structures, as characterized by cell diameter and cell number density. Low-density PU foams are obtained through a process simulating injection molding. The compression properties of reprocessed PU foam are compared with as-synthesized PU foam to demonstrate efficacy of the refoaming processes. These results demonstrate that PU foams can be prepared through recycling while maintaining microstructural and chemical integrity. In the future, this strategy may be applied to thermoset PU foams of various chemical compositions and shows promise for scalability.

A Comparison of Conical and Cylindrical Implants Inserted in an In Vitro Post-Extraction Model Using Low-Density Polyurethane Foam Blocks.

Combining tooth extraction and implant placement reduces the number of surgical procedures that a patient must undergo. Thus, the present study aimed to compare the stability of two types of conical implants (TAC and INTRALOCK) and another cylindrical one (CYROTH), inserted with a range of angulation of 15-20 degrees in low-density polyurethane blocks (10 and 20 pounds per cubic foot, PCF) with or without a cortical lamina (30 PCF), which potentially mimicked the post-extraction in vivo condition. For this purpose, a total of 120 polyurethane sites were prepared (10 for each implant and condition) and the Insertion Torque (IT), Removal Torque (RT), and Resonance Frequency Analysis (RFA) were measured, following a Three-Way analysis of variance followed by Tukey's post hoc test for the statistical analysis of data. The IT and RT values registered for all implant types were directly proportional to the polyurethane density. The highest IT was registered by INTRALOCK implants in the highest-density block (32.44 ± 3.28 Ncm). In contrast, the highest RFA, a well-known index of Implant Stability Quotient (ISQ), was shown by TAC implants in all clinical situations (up to 63 ISQ in the 20 PCF block without the cortical sheet), especially in lower-density blocks. Although more pre-clinical and clinical studies are required, these results show a better primary stability of TAC conical implants in all tested densities of this post-extraction model, with a higher ISQ, despite their IT.

Biomechanical Performance of a Novel Implant Design in Simulated Extraction Sites and Sinuslift Procedures

With increasing experience and in an attempt to shorten overall treatment times, implant placement in combination with tooth extractions and sinus lift procedures has become popular. In both cases, primary stability has to be achieved by either engaging apical and oral regions of trabecular bone or by engaging residual host bone beneath the sinus cavity. Extraction sites were formed by pressing a root analog into homogeneous low density polyurethane foam which was used as bone surrogate while a 3 mm thick sheet of medium density foam was used for mimicking a sinus lift situation. Two types (n = 10) of bone level implants with a conventional tapered design and a cervical back taper (NobelActive; control) and a novel design characterized by a shift in core diameter and thread geometry (AlfaGate; test) were placed in these models following conventional osteotomy preparation. Insertion torque was measured using a surgical motor and primary stability was determined by resonance frequency analysis. Statistical analysis was based on Welch two sample t tests with the level of significance set at α = 0.05. In sinuslifting, NobelActive implants required significantly higher insertion torques as compared to AlfaGate (p = 0.000) but did not achieve greater implant stability (p = 0.076). In extraction sites, AlfaGate implants showed both, significantly higher insertion torques (p = 0.004) and significantly greater implant stability (p = 0.000). The novel implant design allowed for greater primary stability when being placed in simulated extraction sockets and sinuslift situations. While in extraction sockets the position of condensing threads in combination with an increase in core diameter is beneficial, the deep cervical threads of the novel implant lead to superior performance in sinuslift situations.

Primary Stability Assessment of Conical Implants in Under-Prepared Sites: An In Vitro Study in Low-Density Polyurethane Foams

Bone characteristics, the implant macrogeometry, and the drilling technique are considered the main important factors to obtain a good implant primary stability (PS). Indeed, although it is known that implant placement in poor bone sites increases the possibility of implant failure, several surgical procedures have been proposed to improve PS, such as site under-preparation. Hence, this in vitro study aimed to evaluate the insertion torque (IT), removal torque (RT), and resonance frequency analysis (RFA) of conical implants (3.3 and 4 × 13 mm) placed in under-prepared sites on 10 and 20 pounds per cubic foot (PCF) density polyurethane sheets (simulating a D3 and D2 bone, respectively) with and without a cortical sheet of 30 PCF in density (corresponding to a D1 bone). After using ANOVA or Kolmogorov–Smirnov test to elaborate data, the resulting IT and RT values were directly proportional to the polyurethane block densities (e.g., the lowest and highest IT values were 8.36 ± 0.52 Ncm in the 10 PCF density sheet and 46.21 ± 0.79 Ncm in the 20 PCF density sheet + cortical for 4 × 13 mm implants) and increased with the increasing amount of site under-preparation (the highest results for both implants were found with a 2.2 mm under-preparation, showing a significantly higher IT with a p < 0.05 compared with others, especially in the highest-density sheets). Both implants inserted in the 20 PCF density block + cortical with all under-preparation protocols exhibited significantly higher RFA values (p < 0.05–0.0001) compared with the corresponding ones in the 10 PCF block. Moreover, 3.3 × 13 mm implants showed the same results comparing the 20 PCF block and the 10 PCF block + cortical. In conclusion, in this in vitro study using low-density polyurethane blocks, the under-preparation of the implant insertion sites was shown to be effective in increasing implants’ PS.

Are Implant Threads Important for Implant Stability? An In Vitro Study Using Low-Density Polyurethane Sheets

Different strategies are known to improve implant primary stability (PS) and the bone-to-implant contact in post-extractive conditions, such as the macro-geometry of screws and apical threads, which can enhance the mechanical characteristics. In any case, the role of the apical area design in maintaining or improving the PS, especially in low-quality bone, still remains unclear. Thus, the present study aimed at evaluating in vitro the Insertion Torque (IT), Removal Torque (RT), and Resonance Frequency Analysis (RFA) of different implant apical threads in a cylindrical (EE) and in three conical implants (T3, TAC, Intra-lock) inserted in simulated post-extraction conditions on low-density polyurethane foams of 10 and 20 pounds per cubic foot (PCF), with and without the addition of a cortical sheet of 30 PCF in density. The IT, RT, and RFA values of all the implants tested were directly proportional to the polyurethane density and to the presence of the cortical sheet, but TAC and Intra-lock implants, which had the latest-generation thread design, always showed significantly higher values (e.g., IT: 18.6 and 18.6 Ncm, RT: 10.8 and 13.7 Ncm, RFA mean: 46 and 43 ISQ, in the 20 PCF density with the cortical sheet for TAC and Intra-lock, respectively). In particular, TAC implants also reached the highest RFA values in the lowest-density foam (19 ISQ). In conclusion, the present in vitro study demonstrated that TAC and Intra-lock apical designs and macro-geometries could play a key role in determining the PS and the polyurethane-implant contact in simulated post-extraction conditions in low-density artificial bone.

Enhanced effect of chloroprene on the mechanical properties of polyurethane foams

In this research, a new method to increase the mechanical properties of the low-density polyurethane foams (PUFS) has been described. Chloroprene rubber (CR) is used as reinforcing the mechanical properties of the foam. Polyurethane foam (PUF) containing CR (PUF/CR) and pure PUF were characterized by mechanical testing, Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Differential scanning calorimeter (DSC), Thermogravimetric analysis (TGA). The results of mechanical properties show the tensile strength of PUFS containing 0, 1, 2, 3, 4 and 5 wt% CR are 38.2, 42, 56.4, 61.48, 77.3 and 77.18 kPa, respectively. Also the morphological studies show by increasing the amount of CR in the foam structure, the foam cells are smaller and more closed.

Thyroid dose reduction shield with the generation of less artifacts used for fast chest CT examination

Fast chest CT scans with high-pitch factors are effective to reduce motion artifacts, but the over-ranging effect may increase harmful radiation exposure to organs which are located near the outside of the imaging area. This becomes a particular problem during chest CT imaging when managing the radiation dose to the radio-sensitive thyroid, which is located around the upper end of the imaging area. The use of an X-ray shielding material can reduce the exposure dose to the thyroid. However, when the shielding is performed using metal foil, metal artifacts definitely appear, and they interfere with the CT image. To solve this problem, we developed a novel less-artifact thyroid shield in which fine bismuth oxide particles are embedded in low-density polyurethane (PU) foam. This study aims to present the usefulness of our X-ray shield through experimentation using a human body phantom. Three kinds of thyroid shields were used: a commercially-available lead foil as a reference, investigational clay products to evaluate the proper amount of the fine bismuth oxide particles, and bismuth PU shields which are proposed in this study. Furthermore, a bismuth PU shield with an added PU spacer was fabricated for the further suppression of the artifacts. Under clinical conditions, shielding ability and image quality were evaluated. Thyroid doses were measured using small-type OSL dosimeters, and the dose reduction rates were determined. In addition, the image qualities of the thyroid and lung regions were evaluated using a contrast-to-noise ratio (CNR) and an artifact index (AI). When the thyroid is outside the scanning region, thyroid exposure without the shield was caused by over-ranging X-rays and showed 11 mGy. When applying bismuth with an effective mass thickness of 0.12 g/cm2 to the bismuth PU shield, the thyroid exposure dose was reduced by half. In addition, we confirmed that if this shield enters the scanning region through accident, the AI would be less than 10. Also, when using our thyroid shield, the occurrence of metal artifacts was drastically suppressed. In conclusion, our thyroid shield can reduce the radiation exposure dose in half while maintaining acceptable image quality. This is a valuable tool in solving the issue of radiation exposure when performing fast chest CT scans. The shield has breathability and flexibility, and patients can apply the shield to their necks by themselves.

The primary stability of two dental implant systems in low-density bone

Primary stability in low-density bone is crucial for the long-term success of implants. Tapered implants have shown particularly favourable properties under such conditions. The aim of this study was to compare the primary stability of tapered titanium and novel cylindrical zirconia dental implant systems in low-density bone. Fifty implants (25 tapered, 25 cylindrical) were placed in the anterior maxillary bone of cadavers meeting the criteria of low-density bone. The maximum insertion (ITV) and removal (RTV) torque values were recorded, and the implant stability quotients (ISQ) determined. To establish the isolated influence of cancellous bone on primary stability, the implantation procedure was performed in standardized low-density polyurethane foam bone blocks (cancellous bone model) using the same procedure. The primary stability parameters of both implant types showed significant positive correlations with bone density (Hounsfield units) and cortical thickness. In the cadaver, the cylindrical zirconia implants showed a significantly higher mean ISQ when compared to the tapered titanium implants (50.58 vs 37.26; P < 0.001). Pearson analysis showed significant positive correlations between ITV and ISQ (P = 0.016) and between RTV and ISQ (P = 0.035) for the cylindrical zirconia implants; no such correlations were observed for the tapered titanium implants. Within the limitations of this study, the results indicate that cylindrical zirconia implants represent a comparable viable treatment option to tapered titanium implants in terms of primary implant stability in low-density human bone.

Anisotropic thermal expansion of bio-based rigid low-density closed-cell polyurethane foams

Rigid low-density polyurethane (PU) foams containing bio-based components are being increasingly considered as a sustainable substitute for petrochemical resources-based foams for thermal insulation in ambient conditions. However, for applications involving high temperature gradients, the thermal expansivity of foams also has to be characterised. With this aim, rigid low-density polyurethane foams have been manufactured using polyols derived from renewable resources (tall oil fatty acids) and their thermal expansion in the temperature range from 20 to −150 °C was studied. The mean coefficients of linear thermal expansion (CTE) in this range and the differential CTEs at 20 and -150 °C were determined. Increasing the cross-link density of the PU polymer matrix resulted in reduction of the CTEs of both monolithic polymer and closed-cell PU foams. Changing the molecular weight per branching unit of PU from 442 to 318 g/mol caused reduction of the differential CTE of the monolithic PU by about 30% at 20 °C and by 11% at −150 °C. The CTEs of anisotropic foams were expressed in terms of CTE of the polymer and mechanical characteristics of the foams. The predicted CTEs were found to be in good agreement with experimental ones within the temperature range considered.

Investigation on the technology of soft recovery of fragment produced by metal cylindrical shell subjected to explosive loading

According to the requirements on the soft recovery of fragments of expanding cylindrical metal shells under explosion loading, this paper presents a recovery device combining low density polyurethane foam and water medium through theoretical analysis and numerical simulation. Compared to traditional recovery device designed with a single material, the combined recovery device can reduce the amplitude of impact pressure, which is produced by the initial interaction of low impedance polyurethane foam with high speed fragments, by about 1/3 compared to the impact pressure produced by water, and maintain the high decay rate of fragment speed. It can also make full use of the advantages of high density of water medium when the fragment speed is less than 0.5 km/s, which can reduce the decay thickness of the recovery device based on single polyurethane foam. Based on the device, the recovery experiment of expansion and fracture of 304 stainless steel cylindrical shell under explosive loading is carried out. Through the measurement of the wall velocity of the recovery tank and the appearance inspection after the experiment, it is implied that the wall and bottom of the recovery tank are in good condition and can be reused. According to the statistics of the recovered fragments, the recovery rate of the fragments is more than 85%, and the internal and external interfaces of fragments are highly recognizable, the turning blade lines on the surface of the fragments are clearly visible, and several non-penetrating cracks are visible, which verified that the impact damage of the recovery device to the fragments is significantly reduced. Acording to the fracture and surface information of the fragments, the approximate position of the fragments in the metal cylindrical shell is inferred.. Finally, the statistical results of the average thickness and mass distribution of the recovered fragments are given.

Estimation of the effective diffusivity of blowing agents in closed-cell low-density polyurethane foams based on thermal aging data

Low-density closed-cell polyurethane (PU) foams are applied as thermal insulation materials due to their low thermal conductivity imparted by that of the physical blowing agent (PBA) used in foam production. However, foam conductivity tends to gradually increase with time, primarily due to changes in the gas composition in foam cells brought about by gas diffusion. To enable predicting the variation of conductivity during the service life of foam insulation, gas diffusivities are usually determined by measuring the gas composition in foams at different aging times. This study considers an alternative approach of estimating the effective diffusivities of gases in PU foams, which is based on the experimentally determined evolution of foam conductivity. The proposed approach is shown to provide close estimates of the effective diffusion coefficients for PBAs in PU foams when the specimen size and aging duration are such that a significant fraction, ca. 36%, of the PBA leaves the foams during the aging test.

Design and characterization of a multilayered hybrid cored-sandwich panel stiffened by thin-walled lattice structure

Low-density polyurethane (PU) foams have been commonly used for some structural purposes in marine applications. However, they have not been exploited as a structural core because of damage tolerance and durability concerns. The major drawbacks of sandwich panels having PU foam core are their poor mechanical properties and vulnerability to marine environmental conditions. Therefore, the present study aimed to contribute to enhancing both the mechanical properties and environmental durability of the traditional PU foam cored-sandwich panels through introducing a potentially suitable alternative. For this purpose, an innovative panel with a multilayered hybrid core consisting of agglomerate cork and PU foam was proposed which was orthogonally stiffened by a thin-walled lattice structure and sandwiched between two composite skins. To characterize the environmental durability and mechanical properties of this novel panel, a wide range of experimental tests including water immersion conditioning, three-point bending, edgewise and flatwise compression, quasi-static indentation, and high-velocity impact perforation were conducted. The sandwich specimens made of composite skins and PU foam core were also manufactured and tested for comparative purposes. Additionally, a nonlinear finite element (FE) analysis was also carried out and the numerical results were compared with the experimental data. The principal findings were that the proposed structural modifications caused a significant enhancement in all the studied mechanical and durability properties of PU foam-cored sandwich panels. It was also found that the FE model could predict load-displacement behavior of the studied sandwich panels under a variety of experimental conditions.

Reinforcement Efficiency of Cellulose Microfibers for the Tensile Stiffness and Strength of Rigid Low-Density Polyurethane Foams.

Rigid low-density closed-cell polyurethane (PU) foams are widely used in both thermal insulation and structural applications. The sustainability of PU foam production can be increased by using bio-based components and fillers that ensure both enhanced mechanical properties and higher renewable material content. Such bio-based foams were produced using polyols derived from rapeseed oil and microcrystalline cellulose (MCC) fibers as filler. The effect of MCC fiber loading of up to 10 wt % on the morphology, tensile stiffness, and strength of foams has been evaluated. For estimation of the mechanical reinforcement efficiency of foams, a model allowing for the partial alignment of filler fibers in foam struts was developed and validated against test results. It is shown that although applying MCC fibers leads to modest gains in the mechanical properties of PU foams compared with cellulose nanocrystal reinforcement, it may provide a higher content of renewable material in the foams.

Primary Stability of Dental Implants in Low-Density (10 and 20 pcf) Polyurethane Foam Blocks: Conical vs Cylindrical Implants.

Background: The aim of the present study was to compare, in low-density polyurethane blocks, the primary implant stability values (micromobility) and removal torque values of three different implant geometries in two different bone densities representing the structure of the human posterior jaws. Methods: A total of 60 implants were used in the present investigation: twenty implants for each of three groups (group A, group B, and group C), in both polyurethane 10 pcf and 20 pcf densities. The insertion torque, pull-out torque, and implant stability quotient (ISQ) values were obtained. Results: No differences were found in the values of Group A and Group B implants. In both these groups, the insertion torques were quite low in the 10 pcf blocks. Better results were found in the 20 pcf blocks, which showed very good stability of the implants. The pull-out values were slightly lower than the insertion torque values. High ISQ values were found in Group A and B implants. Lower values were present in Group C implants. Conclusions: The present investigation evaluated implants with different geometries that are available on the market, and not experimental implants specifically created for the study. The authors aimed to simulate real clinical conditions (poor-density bone or immediate post-extraction implants) in which knowledge of dental implant features, which may be useful in increasing the primary stability, may help the oral surgeon during the surgery planning.

Flatwise Compression and Local Indentation Response of 3D-Printed Strut-Reinforced Kagome with Polyurethane Filling

Additively manufactured lattice structures are finding wider applications as core materials because of their high specific strength, modulus, and energy absorption. Strut-reinforced Kagome (SRK) structures have been shown to have good compressive performance compared with many existing lattice structures. Herein, the performance of acrylonitrile butadiene styrene (ABS) SRK lattice structures fabricated by fused deposition modeling under flatwise compression and local loading was investigated with and without polyurethane foam fillers. The SRK structure demonstrated abrupt failure at the joints in the vicinity of the face sheet, thereby reducing the energy absorption of the structure. The SRK filled with low-density polyurethane foam had no significant effect on peak failure load and moduli, whereas energy absorption per unit mass was higher by 16.5%. The SRK filled with high-density foam showed 116% increase in energy absorption. Similarly, a stronger indentation response was observed with high-density foam-filled SRK sandwich structures.

Low-density foam as an adhesion facilitator between silicone rubber and copper sheet for use in flexible microwave antennas

An effective solution is presented to address the issue of poor adhesion of metal to silicone for the realization of flexible antennas for wearable applications. The low surface energy of silicone creates difficulties in adhering metal layers to it. Low-density polyurethane (PU) foam is used as an adhesion facilitator for interlocking silicone and a good adhesion strength with the copper layers is obtained via a commercially available polyurethane (PU) binder. The developed multi-layered substrate illustrates a high elongation at break of around 375% and very low water absorbance. The microwave characterizations show that the substrate exhibits a low permittivity value of 2.12 and a loss tangent of 0.02 at 10 GHz. The application of the substrate for wearable purpose is demonstrated by fabricating a simple microstrip antenna and testing its performance in both flat and bending profiles. The antenna characteristics exhibit a gain greater than 7 dB. The gain and bandwidth are almost consistent for all the bending profiles.

Modelling the Strength of Cellulose Nanofiber-Filled Rigid Low-Density PU Foams

Rigid low-density closed-cell polyurethane (PU) foams are used primarily as a thermal insulation material. The foams have to possess a sufficient strength and stiffness in order to ensure their mechanical integrity and dimensional stability in service. The mechanical characteristics of foams are enhanced by adding cellulose nanofibers to the polyol system, which both modify the foaming process and act as a reinforcement of cell struts and walls. A model of composite foam strength is developed based on a regular unit cell and assuming the onset of strut failure as the foam fracture criterion. The load-bearing capacity of foam struts is estimated by the modified Fukuda and Chou model considering the orientation of nanofibers along the strut axis. The model developed is shown to provide a reasonably accurate prediction for the nanofiber loading effect on the strength of composite foams.

Short vs. Standard Length Cone Morse Connection Implants: An In Vitro Pilot Study in Low Density Polyurethane Foam

The aim of the investigation was to evaluate the insertion torque, pull-out torque and implant stability quotient (ISQ) of short implants (SI) and standard length implants (ST) inserted into linearly elastic and constitutive isotropic symmetry polyurethane foam blocks. Short dental titanium implants with a Cone Morse connection and a conical shape (test implants: Test Implant A—diameter 5.5 mm and length 6 mm) (Test Implant B—diameter 5.5 mm and length 5 mm) were used for the present in vitro investigation. ST implants (4 mm diameter and 10 mm length), with a Cone Morse connection and a conical shape, were used as Control Implant A and as Control Implants B. These two latter implants had a different macro design. A total of 20 implants (5 Test A, 5 Test B, 5 Control A and 5 Control B) were used for the present research. The results were similar when comparing the Test A and Test B implants. The test implants had very good stability in polyurethane 14.88–29.76 kgm3 density blocks. The insertion torque values were very high for both types of test implant (25–32 Ncm on 14.88 kgm blocks, and up to 45 Ncm in 29.76 kgm3 blocks). The pull-out test values were very similar to the insertion torque values. The ISQ values were significantly high with 75–80 in 14.88 kgm3 blocks, and 78–83 in 29.76 kgm3 blocks. No differences were found in the values of the Control A and Control B implants. In both these implants, the insertion torque was quite low in the 14.88 kgm3 blocks (16–28 Ncm). Better results were found in the 29.76 kgm3 blocks. The pull-out values for these control implants were slightly lower than the insertion torque values. High ISQ values were found in both control implants (57–80). When comparing SI and ST implants, the SI had a similar if not better performance in low quality polyurethane foam blocks (14.88–29.76 kgm), corresponding to D3 and D4 bone.

Testing and evaluation of full scale fiber-reinforced polymer bridge deck panels incorporating a polyurethane foam core

A fiber-reinforced polymer (FRP) bridge deck panel that incorporates a polyurethane foam core was developed for accelerated bridge construction and repair. This low cost panel was tested under monotonic loading and compared to applicable FRP design equations. This new prototype system consisted of two stiff facesheets of stitch bonded plain-weave woven E-glass fabric with sloping webs of E-glass woven fabric that are separated by trapezoidal-shaped, low-density polyurethane foam. The polyurethane foam was used in an attempt to reduce initial costs. The panels used in this study were manufactured using a one-step, vacuum-assisted, resin transfer molding process (VARTM) using a newly formulated, two-part, thermoset, polyurethane resin developed by Bayer MaterialScience to facilitate the infusion process. The results of the flexural and shear testing indicated that the prototype panels significantly exceeded the AASHTO Design Code Strength requirements by nearly three times. Even more importantly, the panels behaved linearly-elastically throughout the full range of loading and possessed significant post-buckling strength. In addition, the results of these full-scale panels were used to evaluate the applicability of existing FRP design equations when used for the design of the VARTM- manufactured, prototype FRP bridge deck. Results showed that the existing FRP design equations correctly predicted a flexural failure due to local buckling of the compression flange and a bearing failure due local buckling of the webs beneath the concentrated load.

Broadband absorbent materials based on topology optimization design

In this paper, we present a kind of broadband absorbent material. The broadband absorbent material is designed based on topology optimization and tested. The optimizing of metamaterials with a genetic algorithm has become one of the most effective methods of designing metamaterials in recent years. An integral system with interactive simulation of MATLAB and CST Microwave Studio is developed, and the main program of genetic algorithm is written in MATLAB; with simulation and computation in CST the metamaterial is optimized by a genetic algorithm with power of global optimization. Vacuum assistant resin infusion process is a new cost-effective and high-performance process. The proposed radar absorbent material possesses a sandwich structure, which consists of transparent composite skin panel, resistive metasurface, polyurethane foam and reflective composite skin panel. The transparent composite skin panel is low-dielectric-constant glass fiber reinforced composite, which has excellent physical properties and weather resistant property. The core material is composed of low density polyurethane foam and metamaterials, which can well meet the requirements for weight reduction and the invisibility. The reflective composite skin panel is a low-resistance carbon fiber reinforced composite, which prevents the electromagnetic waves from transmitting and also provides electrical boundary conditions for metamaterial. Simulation and test results indicate that the reflectivity of the radar absorbent material is less than-12 dB in a range of 2-18 GHz. Because of the symmetrical structure design of the resistance film, the radar absorbent material is polarization-independent. We preliminarily produce a batch of radar absorbent materials and test their various performances. Such a radar absorbent material has a strong absorption and other properties such as light quality, high temperature resistance, low temperature resistance, humidity resistance and corrosion resistance. The radar absorbent material which has been widely used in the engineering field is easy to achieve the compatibility of absorption, mechanical properties and environmental performance. Compared with previous design method, the topology optimization design is simple in programming operation, good in generality, and short in design periode. The radar absorbent materials owns strong application value.