Space radiation environment adaptability of the domestic 5056 high-performance aluminum honeycomb

In order to investigate the influence of space radiation environment on the performance of domestic 5056 high-performance aluminum honeycomb core, the effects of different irradiation effects and different radiation doses on the nodal strength and mechanical properties of domestic 5056 high-performance aluminum honeycomb core were studied through space radiation environmental tests and mechanical property tests such as high-energy electron irradiation, γ-ray irradiation, ultraviolet irradiation, hot and cold shock test, vacuum volatilization test. The results show that under multiple environmental conditions such as high-energy electron irradiation γ-ray irradiation, ultraviolet irradiation, and hot and cold shock environment, the domestic high-performance aluminum honeycomb core shows excellent adaptability to the irradiation environment and can be used for a long time in the extravehicular environment. However, when the radiation dose is greater than 2 × 109rad, the strength of honeycomb core nodes decreased significantly. The vacuum volatilization test results sindicate that the material meets the gas requirements of aerospace raw materials and has extremely low vacuum pollution characteristics.


Introduction
5056 high-performance ultra-thin aluminum honeycomb core is applied in rigid solar wing of spacecraft [1][2][3] , due to its ultra-light density, ultra-thin aluminum foil thickness, and strong anticorrosion ability (in accordance with MIL-C-5541-1A level anti-corrosion ability), has excellent high temperature resistance, salt spray corrosion resistance, space environment resistance, good conductivity, excellent breathability, and many other excellent properties.Foreign countries have mature research and development technologies for high-performance aluminum honeycomb cores and have formed commercial products for sale, while domestic research started relatively late.
The solar wing substrate, as a large component for external work, is directly exposed to the space environment during service and cannot take corresponding thermal control measures.Therefore, in addition to meeting the requirements of mass and mechanical properties (mainly stiffness, strength, etc.), it also needs to adapt to the space environment, such as space thermal vacuum, temperature fluctuationsand space ionizing radiation.Under these spatial environmental conditions, if the mechanical properties of the honeycomb core decrease, it will cause insufficient substrate strength and damage, ultimately leading to insufficient energy or loss of capability for the entire spacecraft [4][5][6] .
In order to accurately and objectively evaluate the space radiation environment adaptability of spacecraft materials [7][8][9][10] , China Academy of Space Technology, Beihang University, Harbin Institute of Technology, and others have extensively conducted numerical simulation and space environment simulation experimental research in space environment models, environmental effect mechanisms, and spacecraft space environment damage modes [11][12][13][14] .It equipped complete and mature space environment simulators to evaluate the adaptability of spacecraft materials and structures to the space radiation environment.This article conducts high-energy electron irradiation tests on domestically produced 5056 high-performance aluminum honeycomb cores γ Ray irradiation test, ultraviolet irradiation test [15] , cold and heat shock test, vacuum volatilization test [16] , designed different irradiation doses for different tests, comprehensively evaluated the space radiation environment adaptability of domestic 5056 high-performance aluminum honeycomb core, and provided data support for the realization of spacecraft model application of high-performance aluminum honeycomb core.

Node strength specimen
The node strength sample refer to GJB130.3-86"Test Method for node strength of adhesive-bonded aluminum honeycomb core".The sample are cut and tested, and the sample size is (200±10) mm×30mm×T15mm.

Plane compression specimen
The specimens were cut, prepared and tested according to GJB 130.5-86 "Test Method for flatwise compressive properties of adhesive-bonded aluminum honeycomb sandwich-structures and core".The plane compression specimen size was 60mm×60mm×T16mm.

Plane shear strength specimen
Prepare samples and conduct tests respectively according to the standard GJB130.6-86"Test Method for flatwise shear strength of adhesive-bonded aluminum honeycomb sandwich-structures and core", and measure the L and W direction shear strength.The sample size is 150mm×50mm×T13mm.

Vacuum volatilization performance sample
Prepare and conduct testing according to the standard of QJ1558B-2012 "Test Method for volatility performance of materials under vacuum conditions".The sample size is a hexahedron with a side length of 1.5mm~3mm.Before testing, place the sample in a constant temperature and humidity box at room temperature (23±2) ℃ and relative humidity of 45%-55% for 24 h.The ambient air pressure of the equipment during testing is 1×10-3Pa, sample room temperature 125℃±1℃, collection plate temperature 25℃±1℃, test specimen for 24 h

Environmental testing 2.3.1 High-energy electron irradiation test
The high-energy electron irradiation test is conducted on the high-energy electron accelerator device (DD-1.5 high-frequency and high-pressure electron accelerator) shown in Figure 1 (a) in accordance with the requirements of GJB2502.7-2015"Test Methods for Thermal Control Coatings on Spacecraft -Part 7: Vacuum Electron Irradiation Test".After the irradiation test begins, when the absorbed doses reach 1.0×10 15 e/cm 2 (irradiation time 1.4h), 5.0×10 15 e/cm 2 (irradiation time 7h), 1.0×10 16 e/cm 2 (irradiation time 14h) and 2.0× 10 16 e/cm 2 (irradiation time 27.7 h), take out the corresponding node strength samples.After all dose tests are completed and all samples are taken out, refer to the GJB130.3-86bonding aluminum honeycomb core node strength test method to conduct performance tests on the samples.

2.3.2γ-ray irradiation test
γ-ray radiation irradiation test is conducted in accordance with the requirements of GJB2502.10-2015"Test Methods for Thermal Control Coatings on Spacecraft -Part 10: Comprehensive radiation Testing".The 60Co-10E4Ci cobalt source irradiation device (as shown in Figure 1 (b)) was used to simulate the space radiation environment using a cobalt 60 ray source γ Radiation irradiation test.After the irradiation test begins, when the absorbed doses reach respectively 5.0×10 5 rad (irradiation time 1 h), 1.0 × 10 6 rad (irradiation time 2 h), 5.0×10 6 rad (irradiation time 5h) and Take out the corresponding node strength samples at 2.0×10 9 rad (irradiation time 1000h).After all dose tests are completed and all samples are taken out, refer to the GJB130.3-86bonding aluminum honeycomb core node strength test method to conduct performance tests on the samples.

UV irradiation test
The ultraviolet irradiation test is conducted in accordance with the requirements of GJB2502.5-2015"Test Methods for Thermal Control Coatings on Spacecraft -Part 5: Vacuum Ultraviolet Radiation Test".The vacuum ultraviolet irradiation test was conducted in a vacuum ultraviolet irradiation system (as shown in Figure 2 (a)), and the vacuum degree was better than 10-5Pa.The diameter of the vacuum chamber was 600mm, and the equipment irradiation area could reach about 170mm in diameter.The sample irradiation area diameter was about 150mm.After the start of the vacuum ultraviolet irradiation test, when the irradiation time reaches 500ESH (irradiation time 50h), 1000ESH (irradiation time 100h), 1500ESH (irradiation time 150h), 2000ESH (irradiation time 200h), and 3000ESH (irradiation time 300h), the corresponding node strength samples are taken out.After all dose tests are completed and all samples are taken out, refer to the GJB130.3-86bonding aluminum honeycomb core node strength test method to conduct performance testing on the sample.

Thermal Shock
The cold and hot shock tests were carried out in accordance with the requirements of GJB2502.8-2015test methods for thermal control coatings of spacecraft part 8: thermal cycle test.Since the domestic 5056 aluminum honeycomb core material needs to experience high and low temperature cyclic impact process during service, the cold and hot impact test is designed, and the test conditions are: (1) temperature range: -196 ℃ ~+150℃ ; (2) Holding time: maintain for 30 minutes in an environment of+150℃ and for 15 minutes in liquid nitrogen at -196℃ (3) Impact frequency: 200 times.Figure 2 (b) shows the physical picture of the cold and hot shock test.
Cold and hot impact tests were carried out with -196 ℃ liquid nitrogen immersion constant temperature high temperature oven.Impact tests were carried out with L700 × W800 aluminum honeycomb core.After 200 high and low temperature impacts on the honeycomb core, joint strength, plane tension, plane compression, plane shear (L direction) and plane shear (W direction) samples were prepared and tested according to the corresponding standards in Section 2.2.The test was set as a blank control group.After completion, the test data and the room temperature test data are used to evaluate the impact of the cold and hot shock space environment on the performance of the honeycomb core, and calculate the performance retention ratio of the honeycomb core.

The effect of high energy electron irradiation on the strength of honeycomb core nodes
As shown in Figure 3, the node strength and mechanical properties of the honeycomb show a pattern of first increasing and then decreasing with the increase of high-energy electron irradiation dose.This is mainly because the adhesive inside the honeycomb core generally undergoes two reactions after irradiation, cross-linking or degradation.The bond breaking and crosslinking reactions of adhesives are closely related to the structure and environment of the material, as well as the energy loss of irradiated particles in the material.According to the structure and chemical properties of polymers, under the action of high-energy particle radiation, although the two processes of irradiation crosslinking and degradation often coexist, there are primary and secondary processes.For the strength of honeycomb nodes, when the high-energy electron irradiation dose is ≤ 1.×10 15 e/cm 2 , the cross-linking network structure of the adhesive affected by irradiation increases, and the cross-linking reaction caused by irradiation plays a dominant role.Additionally, the incomplete cured adhesive undergoes a certain degree of post curing, which improves the strength and mechanical properties of the honeycomb nodes; When the high-energy electron irradiation dose exceeding 4×10 15 e/cm 2 , the strength and mechanical properties of the honeycomb node decreased, which may be due to the radiation caused the local chemical bond of the adhesive to break the molecular chain, and the radiation degradation played a major role, resulting in a certain degree of de-bonding at the interface, which is not conducive to stress transmission, leading to the decline of the strength and mechanical properties of the honeycomb node.Figure 4 is a physical image of a typical damaged sample in the irradiation test.It can be seen that the typical failure form of the irradiation sample is to pull open from the honeycomb core node and expose the node adhesive interface.Based on the comprehensive analysis of the chart, it can be seen that the strength retention ratio of honeycomb core nodes can be maintained above 90% in all high-energy electron irradiation tests, indicating that the domestically produced material has good adaptability to high-energy electron irradiation environments.

The effect of γ radiation on the strength of honeycomb core nodes
As shown in Figure 5 , when γ radiation dose ≤5×10 6 rad, there was no significant change in the strength and mechanical properties of the honeycomb nodes.This is mainly due to the γ radiation dose ≤ 5 × 10 6 rad, mainly irradiation crosslinking, appropriate γ the thermal effect generated by irradiation under the radiation dose causes partial crosslinking and curing reaction of the adhesive inside the honeycomb node, so the mechanical properties of the strength of the honeycomb node remain basically unchanged.When the radiation dose is greater than 5×10 6 rad, the radiation interpretation dominated, and the adhesive covalent bond (C-C bond and C-H bond) at the honeycomb core node was excited or ionized, resulting in irreversible chemical reaction.When the radiation dose reaches 2×10 9 rad, the node strength sharply decreases.In fact, the space service environment of honeycomb core has been evaluated as 5E6rad, which is a very harsh space environment and due to the extreme testing conditions of 2×10 9 rad radiation measurement (far exceeding the usage environment).Therefore, the domestic honeycomb core can be used for a long time in extravehicular environments.Therefore, the domestic honeycomb core can be used for a long time in extravehicular environments, but for γ Radiation dose greater than 5×10 6 rad, special consideration needs to be given to the strength characteristics of honeycomb core nodes decrease caused by the influence of γ radiation irradiation.

Effect of UV irradiation on the strength of honeycomb core nodes
As shown in Figure 6, the mechanical properties of the honeycomb node strength first increase and then decrease with the vacuum ultraviolet irradiation time increases.The change in node strength with irradiation time is mainly caused by the cumulative effect of ultraviolet irradiation on organic polymer materials.The cumulative effect is irreversible, as organic polymer materials undergo changes in composition and structure after long-term ultraviolet irradiation.Organic polymer materials undergo two types of chemical reactions after UV irradiation: 1) crosslinking of polymer chains.When the molecular weight of polymer materials increases, a three-dimensional network structure is formed when the irradiation dose is high enough; 2) Polymer chain breakage.The average molecular weight decreases, the material softens, and the strength decreases.Therefore, when the strength of the honeycomb node is within a UV irradiation time of ≤ 3000ESH, the thermal effect generated by UV irradiation causes partial irradiation crosslinking of the adhesive inside the honeycomb node strength, leading to a slight upward trend in the strength and mechanical properties of the honeycomb node.When the vacuum ultraviolet irradiation time increase to 3000ESH, the adhesive at the honeycomb core node tends to undergo degradation reactions so that the original components of the adhesive is damaged, resulting in a slight decrease in the strength and mechanical properties of the honeycomb node.Based on the comprehensive analysis of the chart data, it can be seen that under all UV irradiation conditions, the strength of the honeycomb core nodes has slightly increased.Under all dose conditions, the node strength of the honeycomb core meets the requirement of a node strength retention ratio of no less than 99%, indicating that the domestically produced high-performance aluminum honeycomb core has excellent adaptability to UV irradiation space environment.

Influence of thermal shock on mechanical properties of honeycomb core
As shown in table 4, the plane tensile strength, compression strength, shear strength in L direction, and shear strength in W direction all show a certain attenuation compared with the performance retention ratio before impact (blank control group).This is because under extreme low temperature or high temperature conditions, the material rapidly transits from hard and brittle to soften under cold and thermal shock.After 200 cycles, the mechanical properties of the material appear fatigue attenuation, but after all attenuation, the retention ratio of all mechanical properties can be maintained at more than 88%, indicating that the material has good adaptability to cold and hot shock space environment.

Vacuum evaporation performance of honeycomb core
The vacuum total mass loss (TML), condensable volatile matter (CVCM), and water vapor recovery (WVR) test results of the domestically produced 5056 high-performance aluminum honeycomb core are detailed in the table below.As condensable volatile matter is the main cause of pollution to spacecraft products, the data in the table shows that the condensable volatile matter collected during the testing process of the domestically produced 5056 high-performance aluminum honeycomb core is very small, with an average value of 0.018%, Therefore, it is believed that this raw material will not cause harm to external equipment or spacecraft products, and its vacuum pollution is very low.From the data analysis in the table, it can be seen that the total mass loss of the honeycomb core material is 0.101%, with water vapor recovery accounting for 0.048%, approximately 47.52% of the total mass loss, and the rest accounting for 53.48%.This indicates that once the material is placed in a vacuum environment, water will be released, and 47.52% of the 0.101% pollutants under vacuum conditions are water vapor, while the rest are other volatile substances, indicating that the material has extremely low vacuum pollution characteristics.The vacuum volatilization performance of domestic 5056 highperformance aluminum honeycomb core meets the requirements of TML ≤ 1% and CVCM ≤ 0.1% as required by aerospace Q/W776-98 "Non-metallic materials for satellite use exhaust screening method".

Conclusion
This article conducts experimental research on the space environment adaptability of domestic 5056 high-performance aluminum honeycomb core, including high-energy electron irradiation, γ ray irradiation, ultraviolet irradiation, cold and heat shock, vacuum volatilization, etc.After the tests were completed, the nodes strength of honeycomb core was studied and the following conclusions were obtained: (1) Under high-energy electron irradiation conditions, the node strength shows a pattern of first increasing and then decreasing with the increase of high-energy electron irradiation dose.After all dose irradiation tests, the strength retention ratio of honeycomb core nodes can be maintained above 90%, indicating that the domestic material has good adaptability to high-energy electron irradiation environment; (2) Under γ irradiation conditions, irradiation dose ≤5×10 6 rad, there was no significant change in the strength and mechanical properties of the honeycomb nodes; When the radiation dose is greater than 5×10 6 rad, radiation degradation played a dominant role, and the adhesive covalent bond at the honeycomb core node was excited or ionized, resulting in irreversible chemical reaction that degraded the physical and chemical properties.When the radiation dose reaches 2 ×10 9 rad, the node strength sharply decreases.In fact, the space service environment of honeycomb core has been \ evaluated as 5E6, which is a very harsh space environment and due to the extreme testing conditions of 2E9rad radiation measurement (far exceeding the usage environment).Therefore, the domestic honeycomb core can be used for a long time in extravehicular environments.
(3) Under all UV irradiation conditions, the strength of honeycomb core nodes showed a slight increase.Under all dose conditions, the strength of honeycomb core nodes meet the requirement of node strength retention ratio not less than 99%, indicating that the domestic high-performance aluminum honeycomb core has excellent adaptability to UV irradiation space environment; (4) Under the condition of cold and hot shock, the node strength, plane tensile strength, compression strength, L-direction shear strength, and W-direction shear strength of the honeycomb core decreased to a certain extent compared with the performance retention ratio before impact, but the retention ratio of all mechanical properties can be maintained at more than 88%, indicating that the material has good adaptability to the cold and hot shock space environment; (5) The vacuum volatilization performance of domestically produced 5056 high-performance aluminum honeycomb core meets the requirements of TML ≤ 1% and CVCM ≤ 0.1% required by Aerospace Q/W776-98 "Non-metallic materials for satellite purposes screening method", indicating that the material has extremely low vacuum pollution characteristics.
Fig.1 Environmental Test (a) Ultraviolet irradiation test (b) cold and hot shock test(thermal shock test??) Fig.2 Environmental Test

Table 1
Statistical Table of High Energy Electron Irradiation Experiment Result

Table 2
Statistical table of γ radiation experiment results

Table 3
Statistical Table of UV Radiation Experiment Results

Table 4
Comparison of Performance of Imported Honeycomb after Impact (Unit: MPa)

Table 5
Vacuum Volatility Performance of Honeycomb Core (Unit: MPa)