Buoyancy Material Research Articles

Hydraulic pressure resistance of the ceramic resin composite buoyancy materials based on cylindrical tube configuration

Due to high modulus, high strength and low water absorption of the 99.5% alumina ceramic, the tubular ceramic resin composite (TCRC) has been designed and fabricated, which can provide a potential option for the deep-sea buoyancy materials. The reliability and applicability of TCRC under hydrostatic pressure are systematically discussed by means of theory, experiment and simulation. Circumferential instability and strength failure are two possible failure modes of the TCRC through theoretical analysis. The study indicates that the load-bearing capacity of TCRC decreases with the increase of the number of vertical/horizontal tube arrays m, the ratio of the inner to outer radius r/Rc of the ceramic tube or the ratio of the length to the outer radius L/Rc of the ceramic tube. Conversely, the load-bearing capacity of TCRC increases with the increase in the modulus of matrix phase Er. In addition, TCRC with parameters of “r/R-0.93/0.91-3X3-L40-E3.18” has excellent performance through experimental verification. That is, the core density and hydrostatic strength of the TCRC are 0.67 g/cm3 and 150.6 MPa, respectively. Better stated, our designed buoyancy material can be applied in the deep-sea environment of 12000m, which is the deepest spot on the ocean floor ever explored. The excellent performance of TCRC verifies the feasibility of ceramic circular honeycomb configuration in the application of hydrostatic pressure environment. Meanwhile, the buoyancy materials used in different water depths can be designed by changing the L/Rc or r/Rc of the round tube in circular honeycomb.

Study of Ceramic Hollow Buoyant Balls Prepared Based on Slip Mold Casting and Brazing Process

In the domain of deep-sea buoyancy material applications, hollow ceramic spheres, known for their high strength and low mass-to-drainage ratio, contribute to increased buoyancy and payload capacity enhancement for deep submersibles, constituting buoyancy materials of exceptional overall performance. This study entails the brazing of two ceramic hemispherical shells, obtained through slurry molding, to form a ceramic float. This process, which integrates slurry molding and ceramic brazing, facilitates buoyancy provision. Further refinement involves welding a ceramic connector onto the ceramic shell, incorporating a top opening to create a ceramic float equipped with an observation window seat. The ceramic float maintains uniform wall thickness, while the observation window facilitates external environmental observation in deep-sea research. Two pressure-resistant spherical shells, produced using this process, underwent testing, revealing the wall thickness of the prepared alumina ceramic hollow spheres to be 1.00 mm, with a mass-to-drainage ratio of 0.47 g/cm3 and a buoyancy coefficient of 53%. The resultant ceramic hollow floating ball can withstand hydrostatic pressure of 120 MPa, while the pressure-resistant ball shell with an observation window seat can endure hydrostatic pressure of 100 MPa, ensuring safe operation at depths of 5000–6000 m. This process provides a production method for subsequent large-scale ceramic float manufacturing for the transportation of objects or personnel.

Temperature and strain gradient monitoring of the buoyancy material curing reaction with a submillimeter spatial resolution fs-FBG array

Millimeter-scale temperature and strain gradient measurements are crucial for understanding the mechanical properties of buoyancy materials. In this paper, we successfully fabricated ultrashort and high-density fiber Bragg grating (FBG) array based on femtosecond laser point-by-point writing technology. By optimizing the energy and number of femtosecond laser pulse, and introducing secondary tilt apodization technology, submillimeter-spatial-resolution FBG arrays were prepared. To the best of our knowledge, this is the first application of femtosecond FBG array for high spatial resolution temperature and strain gradient in situ monitoring of buoyancy materials. FBGs exhibit excellent anti-chirp performance and achieve submillimeter spatial resolution curing monitoring under temperature and strain monitoring gradients of 2.6 °C/mm and 231 με/mm, respectively.

Fabrication and Compression Properties of Reinforced Epoxy Syntactic Foam With Basalt Fiber

Deep‐sea equipment is generally made of lightweight and pressure‐resistant materials in order to meet the requirements of the actual work. In order to explore marine resources better, it is necessary to research lightweight buoyancy materials for loading on mining equipment. These buoyancy materials contribute not only to providing adequate buoyancy to the mining equipment but also to reducing economic expenses. In this paper, hollow glass microspheres reinforced epoxy hollow spheres (HGMSs‐EHSs) were prepared by the rolling ball method using expanded polystyrene (EPS), epoxy resin (EP), and HGMS as raw materials. Epoxy syntactic foam (ESF) was manufactured by blending EP, curing agent, HGMS, and HGMS‐EHS with molding method. Basalt fiber (BF) reinforced ESF was fabricated by adding BFs to form a fiber network inside the syntactic foam. The results revealed that the density and compressive strength of ESF increased progressively with the number of HGMS‐EHS layers. The density and compressive strength of ESF decreased prospectively with the increase of the stacking volume fraction of HGMS‐EHS. The density and compressive strength of ESF increased gradually with the enlargement of the length and content of BF. In the range of influencing factors mentioned above, the density of ESF remains around 0.3 g/cm3, which has a low density. When the number of layers of HGMS‐EHS was two, the stacking volume fraction was 90%, the length of BF was 12 mm, the content of BF was 4%, the density of BF‐ESF was 0.316 g/cm3, and the compressive strength was 6.93 MPa. The compressive strength of prepared buoyancy material can meet the pressure resistance requirements for operations in waters of a certain depth. With a density of only 0.316 g/cm3, it provides sufficient buoyancy to balance the gravity of the equipment. Compared with the current study, in this paper, BFs were used as the reinforcing phase to prepare solid buoyancy foam with low density and high compressive strength. The experimental results demonstrate that this economical fiber material can effectively improve the compressive strength of buoyancy materials. This buoyancy material may be suitable for loading on small equipment for extracting marine resources. This work provides a reference for the preparation of low‐density solid buoyancy materials.

A method for improving the hydrostatic pressure testing of the compressive strength of solid buoyancy materials used at full ocean depth

The current optimized synthesis methods for solid buoyancy materials used in manned submersibles at full ocean depth fail to meet the safety factor requirement of 1.5 specified in China Classification Society rules. To address this issue, this study proposes a novel method for enhancing the compressive strength and safety margin of such materials using hydrostatic pressure to screen hollow glass microspheres and eliminate those with low compressive strength. The as-prepared solid buoyancy material is free of surface cracks and has a water absorption rate of <0.1% after a 24-h hydrostatic pressure test at 175 MPa, satisfying the required safety performance standards for buoyancy materials used at full ocean depth. This study highlights the feasibility of using hydrostatic pressure testing to enhance the compressive strength and safety of solid buoyancy materials for full-ocean-depth applications, paving the way for the development of more advanced and reliable buoyancy materials for deep-sea exploration.

Compressive model and numerical simulation analysis of a low-weight and high-strength structure combined with a buoyancy material and FRP

ABSTRACT The requirements of low weight and high strength are often contradictory in the design and production of manned/unmanned submersibles. In this paper, a novel structure that combines fiber-reinforced composites and buoyancy materials was proposed to solve this contradiction. These two materials in this structure can cooperate and obtain good compressive properties and low densities. A theoretical model of the compressive strength of this combined structure is proposed. Compression experiments were carried out on six groups of samples. The experimental results show that the compressive capacity of the combined structure is greater than the sum of the compressive capacity of buoyancy material and FRP pipe. The stress distribution of the combined structure under uniaxial pressure is simulated through a finite element model. The numerical simulation results and theoretical predictions show good agreement with the experimental data.

Design of lightweight damping core for composite sandwich structure

AbstractThe damping performance and lightweight design requirements of composite sandwich structure core were studied. A series of low density damping cores were prepared by blending epoxy/polyurethane graft copolymer (E‐g‐U) and epoxy/poly mercaptan block copolymer (E‐b‐M) with different contents of hollow glass beads (HGM). The damping properties, mechanical properties, density, and interface morphology of the core layer were studied. The damping response and flexure properties of the sandwich composite structure were studied by modal analysis and three‐point flexure test. The experimental results show that optimal damping performance of matrix appears at 60% E‐b‐M ratio, the peak loss factor is 0.88, and the damping temperature range covers −2 ~ 52°C. When the HGM content in the core is 10 phr, the density can be comparable to that of the buoyancy material. Under flexural load, the ultimate shear strength and shear modulus of the sandwich structure increase maximum at 15 phr and 10 phr, respectively. Compared with the unfilled HGM sample, the first three modal damping ratios of the sandwich structure are increased by 133.2%, 56.6%, and 56% by 10 phr damping core, respectively. The results are compared with those in other reference. The research shows that the design of lightweight damping core is expected to provide a core material selection for the vibration reduction of sandwich structures.

Fatigue Analysis of the Oil Offloading Lines in FPSO System under Wave and Current Loads

In this paper, fatigue analysis of oil offloading lines (OOLs) in the floating production storage and offloading (FPSO) catenary anchor leg mooring (CALM) buoy offloading system under wave and current loads in the West Africa Sea area is carried out by the numerical simulation method. The hydrodynamic coupling response is calculated, and fatigue damage is analyzed. Firstly, the numerical model is verified by comparison with the experimental results. Then, according to the environmental statistics in West Africa, the influence of various parameters on the fatigue damage of OOLs is analyzed, including tension characteristics, wave parameters, and structural parameters. Additionally, the effect of current load is studied. Results show that accumulated fatigue damage mainly occurs near the CALM buoy and is mainly caused by the 0° wind wave. Appropriately reducing the cover length of buoyancy material and increasing the wall thickness can reduce fatigue damage. Moreover, the effect of the shuttle tanker can increase the fatigue damage of the OOL near the CALM buoy by about 1.5 times, and the effect of vortex-induced vibration can increase the fatigue damage of the OOL in the middle part by up to 5–10 times.

Design and characterization of the carbon fiber tube reinforced polymer composite for full ocean depth submersibles

The large difference between in-plane and out-of-plane mechanical properties limits the application of traditional composite honeycombs in submersibles. In this work, the carbon fiber tube reinforced polymer composite (CTPC) which have lightweight characteristic and high hydrostatic strength is designed and manufactured. The combination between epoxy resin and carbon fiber tube inhibits the buckling failure and improves the bearing capacity of the tube. Resin binds carbon fiber tubes and forms a stable stress transmission path between them. The hydrostatic response of the CTPC has been investigated by simulation and test. The measured results show good agreement with the simulation. Due to its high hydrostatic bearing capacity and lightweight, the CTPC can be used as a new type of buoyancy material in submersibles.

Numerical simulation and experimental study on flexible buoyancy material of hollow glass microsphere and silicone rubber for small deep-sea soft robots

As a novel type of robot, soft robots are used in various subtle scenes. Buoyancy materials used in small deep-sea soft robots need to have characteristics of low density and certain flexibility. Thus, in order to adapt the flexible buoyancy material (FBM) underwater equipment to the complex deep sea environment, hollow glass microspheres (HGMs) are used as fillers and silicone rubber (SR) as matrix to prepare FBM. The main properties, such as density, tensile strength, elastic modulus, hardness and water absorption are tested and analyzed to make the preparation of FBMs serialized. Scanning electron microscope (SEM) is used for morphological observations, which can distinguish the bubbles and broken HGMs in FBMs. Moreover, digital image processing (DIP) method is used to determine the content of the impurity phase in the material. Then, the influences of the impurity phase on the properties of the material are also studied. In addition, the reason of hardness change is analyzed by micro element simulation method. Results show that the performance of FBMs is relatively balanced when the mass fraction of HGM is 20%. FBMs can be used as structural material or buoyancy material of small underwater soft robots for tests and applications.

Compression molding process and performance of hollow glass microsphere/epoxy resin solid buoyancy materials

A vacuum-assisted compression molding and free curing method suitable for the preparation of epoxy resin-based solid buoyancy materials was proposed by learning from the ceramic material molding process, which realized the separation of molding and solidification during the preparation of solid buoyancy materials and provided a new method for the preparation of high performance solid buoyancy materials. The epoxy resin (E-4221) was used as the matrix, and the hollow glass microsphere (HGMS) was used as the filling material. The HGMS/E-4221 solid buoyancy material with high HGMS volume fraction was prepared by compression molding and free curing method. The effects of volume fraction of HGMS and molding pressure on the density, compressive strength and water absorption of HGMS/E-4221 solid buoyancy materials were studied. The results show that the vacuum-assisted compression molding and free curing method is suitable for the preparation of HGMS/E-4221 solid buoyancy materials with HGMS volume fraction of 65%-67%. The obtained HGMS/E-4221 solid buoyancy material has a den-sity of 0.621-0.655 g/cm3 and a suitable depth of 8 000-10 000 m.

Experimental investigation of the hydrostatic compression of a hollow glass microspheres/epoxy resin under high‐pressure conditions at the full ocean depth

AbstractAn experimental study was performed on a new composite material, namely, a hollow glass microsphere/epoxy resin composite material. As a new type of solid buoyancy material, the proposed composite material is promising for use in submersible, deep‐sea oil risers. This composite material has many advantages, including the ability to bear extreme temperature, corrosion, and hydrostatic pressure up to tens of megapascals. In this study, the hydrostatic compression properties of six different mass filling ratio samples were tested based on an advanced triaxial testing system with varying temperatures. Some basic parameters, such as density, axial and radial stress‐strain curves, and volume strain, were obtained. The elastic modulus and Poisson's ratio were subjected to nonlinear fitting. Additionally, the elastic‐plastic performance was analyzed according to the residual strain. A new method to characterize the properties of the material is proposed. These data will be used to develop new constitutive models and to predict the structural strain in engineering applications under high hydrostatic compression.

Effect of the Aromatic Amine Curing Agent Structure on Properties of Epoxy Resin-Based Syntactic Foams.

Epoxy resin is one of the commonly used matrixes of syntactic foams as a buoyancy material, the curing agents of which affect some of the properties for syntactic foams. Therefore, the curing reactions of N,N,N′,N′-tetraepoxypropyl-4,4′-diaminodiphenylmethane (AG-80) epoxy resin between 4,4-diaminodiphenyl methane (DDM) and the mixture of m-xylylenediamine and DDM (DDM-m-XDA) systems are studied. The DDM mixed with m-XDA enhances curing reactions with the AG-80 epoxy resin, and the mechanisms of the two curing systems are different through nonisothermal kinetics. Compared with a single curing system, there are some wrinkles on the surface of the AG-80/DDM-m-XDA matrix because of the disordered network. Composited with hollow glass microspheres (HGMs), the more flexible m-XDA structure enhances the interfacial adhesion between the matrix and HGM for syntactic foams. However, the wrinkles in the matrix increase the broken degree of HGMs; especially at HGM contents higher than 55%, the flaw increases the density and water absorption of syntactic foams; meanwhile, it decreases the compressive strength. Therefore, the properties of syntactic foams can be improved by mixing different molecular structure curing agents and the mixture liquid curing agent simplifies the preparation process to some extent.

Tetrafunctional Epoxy Resin-Based Buoyancy Materials: Curing Kinetics and Properties.

In order to synthesize a new kind of buoyancy material with high-strength, low-density and low-water-absorption and to study the curing reaction of tetraglycidylamine epoxy resin with an aromatic amine curing agent, the non-isothermal differential scanning calorimeter (DSC) method is used to calculate the curing kinetics parameters of N,N,N′,N′-tetraepoxypropyl-4,4′-diaminodiphenylmethane epoxy resin (AG-80) and the m-xylylenediamine (m-XDA) curing process. Further, buoyancy materials with different volume fractions of hollow glass microsphere (HGM) compounded with a AG-80 epoxy resin matrix were prepared and characterized. The curing kinetics calculation results show that, for the curing reaction of the AG-80/m-XDA system, the apparent activation energy increases with the conversion rates increasing and the reaction model is the Jander equation (three-dimensional diffusion, 3D, n = 1/2). The experimental results show that the density, compressive strength, saturated water absorption and water absorption rate of the composite with 55 v % HGM are 0.668 g·cm−3, 107.07 MPa, 0.17% and 0.025 h−1/2, respectively. This kind of composite can probably be used as a deep-sea buoyancy material.

Curing and Characteristics of N,N,N′,N′-Tetraepoxypropyl-4,4′-Diaminodiphenylmethane Epoxy Resin-Based Buoyancy Material

Buoyancy material is a type of low-density and high-strength composite material which can provide sufficient buoyancy with deep submersibles. A new buoyancy material with N,N,N′,N′-tetraepoxypropyl-4,4′-diaminodiphenylmethane epoxy resin (AG-80) and m-xylylenediamine (m-XDA) curing agent as matrix and hollow glass microsphere (HGM) as the filler is prepared. The temperature and time of the curing process were determined by the calculations of thermal analysis kinetics (TAK) through differential scanning calorimetry (DSC) analysis. The results show that the better mass ratio of AG-80 with m-XDA is 100/26. Combined TAK calculations and experimental results lead to the following curing process: pre-curing at 75 °C for 2 h, curing at 90 °C for 2 h, and post-curing at 100 °C for 2 h. The bulk density, compressive strength, and saturated water absorption of AG-80 epoxy resin-based buoyancy material were 0.729 g/cm3, 108.78 MPa, and 1.23%, respectively. Moreover, this type of buoyancy material can resist the temperature of 250 °C.

Determining the Damage Mechanisms for Buoyancy Materials of Deep-Sea Manned Submersibles

Zhang, Y.; Ding, Z.; Wang, Y.; Zhao, Q., and Qin, S., 2019. Determining the damage mechanisms for buoyancy materials of deep-sea manned submersibles. Journal of Coastal Research, 35(5), 996–1002. Coconut Creek (Florida), ISSN 0749-0208.Deep-sea manned submersibles are important platforms for ocean exploration, and their structural reliability is critical to the personal safety of the crew. In particular, the buoyancy materials of deep-sea manned submersibles are vital parts because they provide the necessary buoyancy for submersible operations. This paper first describes the overall damage of the buoyancy materials used in the deep-sea manned submersible Jiaolong that accumulated over a large number of research expeditions during years of services. The causes of the damage are analyzed by computational fluid dynamics (CFD) methods. Because Jiaolong's buoyancy materials are secured to its structural frame by bolts, the external forces that act on the submersible are concentrated on these bolts. Those external forces include the wave forces that act on the submersible when it floats on the sea surface and the buoyancy material shrinkage that occurs because of changes in environmental pressure and temperature during submarine operations. Finally, several suggestions are provided for improving the design and operation of deep-sea submersibles.

Preparation and Investigation of Epoxy Syntactic Foam (Epoxy/Graphite Reinforced Hollow Epoxy Macrosphere/Hollow Glass Microsphere Composite)

Graphite reinforced hollow epoxy macrospheres (GR-HEMS) and hollow glass microspheres (HGMS) were used to prepare three phase epoxy syntactic foam (ESF) using “molding method”, and the physical and mechanical properties of ESF were also studied and investigated. An innovative “rolling ball method” was implemented in the GR-HEMS preparation process. The performance tests show that higher GR-HEMS stacking volume fraction, lower GR-HEMS thickness, higher GR-HEMS diameter, higher HGMS volume fraction, lower HGMS density are beneficial to reducing the density of ESF, but the effects of the five factors on the strength of ESF are the opposite. Therefore, in order to obtain “high strength and low density” ESF composites, the various factors should be considered to achieve a balance of the strength and the density. Scanning electron microscope (SEM) shows that the “rolling ball method” can make graphite form a graphite spherical x-y network throughout the macrosphere wall, which can make GR-HEMS and ESF have great compressive strength. The ESF (450 kg/m3, 20.75 MPa) can withstand the 2075 meters water pressure and provide 550 kg/m3 buoyancy, which can give some advice to the preparation of buoyancy material used in deepwater oil exploration.

Fabrication and mechanical properties of a novel epoxy-hollow glass microsphere composite

According to the demand of deep-sea buoyancy material with high compression strength and low density, a novel epoxy-hollow glass microsphere composite was manufactured and characterized. Firstly, the epoxy resin is modified by chemical modification methods using poly(methyltriethoxysilane) to improve the toughness of epoxy resin. Then, the ammonium bicarbonate is used as the foaming agent to add into the epoxy resin to produce the bubbles. After mixing with a small amount of hollow glass microsphere, the modified epoxy-hollow glass microsphere composite with foams is fabricated. IR spectrum indicates that the silicone has been successfully grafted on the epoxy resin chain, which benefits the toughness of the resin. It can be found that a lot of smaller bubbles exist on the surface of hollow glass microsphere by SEM, which further reduces the density of the modified epoxy-hollow glass microsphere composite. The compression strength has been significantly improved since the bubbles on the surface of glass beads play the role of a buffer balloon and there are few air bubbles in the resin matrix. The coefficient of water absorption for the modified epoxy-hollow glass microsphere composite also increased. The flexural strength of the modified epoxy-hollow glass microsphere composite was slightly reduced at the same time. The results here confirm a promising method for buoyancy materials to promote the compression strength and reduce the density.

Mechanical properties and high-temperature resistance of the hollow glass microspheres/borosilicate glass composite with different particle size

Buoyancy material with high temperature resistance was successfully prepared through a tert-butyl alcohol gelcasting process. Borosilicate glass (BG) and hollow glass microspheres (HGMs) with different average diameters were used as the matrix and the filler, respectively. Results show that the compressive strength increased with the decrease of the mean diameter of HGMs, and the sample consisting of the filler of HGMs with a small average diameter exhibited high compressive strength of 25.04 MPa. Young's modulus values of the composite sintered at 700 °C and 750 °C were distributed over in the range of the values predicted from Ashby-Gibson model to Hashin-Shtrikman model and other moduli values agreed well with that of Past model prediction. Weibull moduli (m) reflecting the variation degree of the sample compressive strength were in the range of 5–15. The compressive strength of the composites composed of the HGMs with small average particle size tested at 500 °C was as high as 7.94 MPa.

Development of a buoyancy material of hollow glass microspheres/SiO2 for high-temperature application

A type of buoyancy material with excellent temperature resistance was successfully prepared through a molding method, and the hollow glass microspheres (HGMs) and silicon oxide (SiO2) were used as the filler and the matrix, respectively. The effect of sintering temperature on mechanical performance, microstructure, and high-temperature performance of the HGMs/SiO2 composite were investigated in the study. The HGMs/SiO2 composite exhibited low density (0.47–0.53 g/cm3), high porosity (66.7–75.6%), low thermal conductivity (0.18–0.27 W/(m·K)), and relatively high compressive strength (3.8–5.2 MPa) properties. The values of Weibull moduli m used to predict the variation degree of compressive strength during the compression process was in the range of 5–15 and its values for the samples sintered at 850 °C was 14.64. Two stages namely elastic stage and fracture stage were shown in the stress-strain curves and in the elastic stage, the stress increased linearly with increasing of the strain until reaching the maximum stress. In the fracture stage, the sample gradually destroyed with further increasing of the strain until complete failure. The compressive strength of the HGMs/SiO2 composites tested at high-temperature was larger than that of the one tested at room temperature. The HGMs/SiO2 composite exhibited low density, low thermal conductivity and excellent temperature resistance properties and can be used as the structural material or buoyancy material in the deep sea field in the near future.