Structural optimization approach for specially shaped composite tank in spacecrafts

This study proposes an optimized approach of designing in which a model specially shaped composite tank for spacecrafts is built by applying finite element analysis. The composite layers are preliminarily designed by combining quasi-network design method with numerical simulation, which determines the ratio between the angle and the thickness of layers as the initial value of the optimized design. By adopting an adaptive simulated annealing algorithm, the angles and the numbers of layers at each angle are optimized to minimize the weight of structure. Based on this, the stacking sequence of composite layers is formulated according to the number of layers in the optimized structure by applying the enumeration method and combining the general design parameters. Numerical simulation is finally adopted to calculate the buckling limit of tanks in different designing methods. This study takes a composite tank with a cone-shaped cylinder body as example, in which ellipsoid head section and outer wall plate are selected as the object to validate this method. The result shows that the quasi-network design method can improve the design quality of composite material layer in tanks with complex preliminarily loading conditions. The adaptive simulated annealing algorithm can reduce the initial design weight by 30%, which effectively probes the global optimal solution and optimizes the weight of structure. It can be therefore proved that, this optimization method is capable of designing and optimizing specially shaped composite tanks with complex loading conditions

Numerical optimization of soft-mold aided co-curing process of advanced grid-stiffened composite structures

The co-curing process for advanced grid-stiffened (AGS) composite structure is a promising manufacturing process, which could reduce the manufacturing cost, augment the advantages and improve the performance of AGS composite structure. An improved method named soft-mold aided co-curing process which replaces the expansion molds by a whole rubber mold is adopted in this paper. This co-curing process is capable to co-cure a typical AGS composite structure with the manufacturer’s recommended cure cycle (MRCC). Numerical models are developed to evaluate the variation of temperature and the degree of cure in AGS composite structure during the soft-mold aided co-curing process. The simulation results were validated by experimental results obtained from embedded temperature sensors. Based on the validated modeling framework, the cycle of cure can be optimized by reducing more than half the time of MRCC while obtaining a reliable degree of cure. The shape and size effects of AGS composite structure on the distribution of temperature and degree of cure are also investigated to provide insights for the optimization of soft-mold aided co-curing process

Structural Significance of His73 in F-Actin Dynamics: Insights from Ab Initio Study

F-actin dynamics (polymerization and depolymerization) are associated with nucleotide exchange, providing the driving forces for dynamic cellular activities. As an important residue in the nucleotide state-sensing region in actin, His73 is often found to be methylated in natural actin and directly participates in F-actin dynamics by regulating nucleotide exchange. The interaction between His73 and its neighboring residue, Gly158, has significance for F-actin dynamics. However, this weak chemical interaction is difficult to characterize using classic molecular modeling methods. In this study, ab initio modeling was employed to explore the binding energy between His73 and Gly158. The results confirm that the methyl group on the His73 side chain contributes to the structural stability of atomistic networks in the nucleotide state-sensing region of actin monomers and confines the material exchange (Pi release) pathway within F-actin dynamics. Further binding energy analyses of actin structures under different nucleotide states showed that the potential model of His73/Gly158 hydrogen bond breaking in the material exchange mechanism is not obligatory within F-actin dynamics

Numerical investigation into the buckling behavior of advanced grid stiffened composite cylindrical shell

Advanced grid stiffened composite cylindrical shell is widely adopted in advanced structures due to its exceptional mechanical properties. Buckling is a main failure mode of advanced grid stiffened structures in engineering, which calls for increasing attention. In this paper, the buckling response of advanced grid stiffened structure is investigated by three different means including equivalent stiffness model, finite element model and a hybrid model (H-model) that combines equivalent stiffness model with finite element model. Buckling experiment is carried out on an advanced grid stiffened structure to validate the efficiency of different modeling methods. Based on the comparison, the characteristics of different methods are independently evaluated. It is arguable that, by considering the defects of material, finite element model is a suitable numerical tool for the buckling analysis of advanced grid stiffened structures

A Partitioning Method for Friction Stir Welded Joint of AA2219 Based on Tensile Test

The partition of aluminum alloy welded joint often depends on microscopic methods such as scanning electron microscopy before. This paper provides a novel partitioning method, which can obtain the material properties and partition results at the same time based on tensile test. The mechanical properties of every point on the whole welded joint are first obtained by the digital image correlation (DIC) method. Then, the mechanical property function of the weld joint along the weld center is established due to the changes of plastic property and strain hardening exponent at each point and the boundary between different areas is then determined. Metallographic detection technology and nano-mechanical testing techniques are employed to validate this partitioning scheme. The partition result of the strategy proposed in this paper is consistent with the partitioning result of the classical method. Compared to classical method, the proposed partitioning method is more practical and effective, as it can obtain mechanical properties and partition boundary through a single tensile test and reduce the cost of metallographic test

Investigations on the mechanical behavior of composite pipes considering process-induced residual stress

Hydrogen, as a clean energy source, has gained worldwide attention due to its high energy density and diverse manufacturing methods. Pipeline transportation is the most important way for long-distance transportation of hydrogen. However, hydrogen embrittlement due to hydride formation in metals will induce cracking in the pipeline structures. Composites pipes are good alternatives to metals as their excellent compatibility with hydrogen. This paper aims to carry out the preliminary design of composite hydrogen transportation pipelines. Firstly, the Thermo-Consolidation/Curing-mechanical analysis models for the thermosetting composites (T700/3501-6) and thermoplastic composites (T700/HDPE) were established, respectively. The process-induced residual stress of the composite pipelines was predicted by the models. Subsequently, a criterion of hydrogen leakage for the composite pipelines was proposed, and the load-bearing capacity analysis of the composite pipelines was carried out based on the progressive damage model. The simulation results emphasize that the predicted leakage pressure would be overestimated without considering the process-induced residual stress. The leakage pressures of composite pipelines with and without liner are calculated and compared, the results showed that the thermoplastic composite pipes with liner are the most suitable for hydrogen transportation.This work was supported by the Science and Technology Innovation Foundation of Dalian (No. 2020JJ25CY011)

Lightweight and Flexible Graphene Foam Composite with Improved Damping Properties

As an elastomer, PDMS can effectively suppress vibration in various fields in a certain temperature range by its viscoelastic behavior in the vitrification transition region, but the vibration isolation effect is poor at high temperature. In this paper, a three-dimensional graphene oxide (GO) foam is fabricated by solution processing method and freeze-drying techniques. After sequential infiltration synthesis, a GO-foam-reinforced PDMS nanocomposite (GO/PDMS) is fabricated with improved damping ability. By adjusting the content of GO, the micros-tructure of GO foam can be sensitively changed, which is crucial to the damping properties of composites. In this paper, by the dynamic mechanical analysis (DMA) of pure PDMS and five kinds of GO/PDMS composites, it is proved that the GO/PDMS composites developed in this work have reliable elasticity and viscoelasticity at 25 °C, which is 100 °C higher than the applicable temperature of pure PDMS. The storage modulus can reach 3.58 MPa, and the loss modulus can reach 0.45 MPa, which are 1.87 times and 2.0 times of pure PDMS, respectively. This GO-based nanocomposite is an ideal candidate for damping materials in passive vibration isolation devices

Numerical and Experimental Failure Analysis of Carbon Fiber-Reinforced Polymer-Based Pyrotechnic Separation Device

Current pyrotechnic separation devices are mainly made of metal materials, limiting the capacity of lightweight design in advanced launching vehicles. With the outstanding mechanical properties, such as high mass-specific strength and modulus, carbon fiber-reinforced polymers (CFRPs) have the potential to replace metal materials in pyrotechnic seperaton devices. However, to improve the seperation reliability of these pyrotechnic separation devices, there still needs further understanding on the the failure mode of CFRP composites under linear shaped charge (LSC). In this paper, cutting tests were carried out on CFRPs for the failure analysis of CFRPs under LSC, and nonlinear finite element analysis (FEA) was performed to characterize the evolution of LSC cutting in CFRPs. According to experimental simulation and numerical simulation, it can be found that the three main failure modes in CERPs while subjected to LSC jet are shear failure, delamination failure, and tensile failure. In the early cutting stage, the initial time of damage of the fiber and the matrix near the shaped charge shows less difference and the laminate is directly separated by the energy of high-speed jet. When the jet velocity decreases, the jet morphology collapses and matrix damages precede into the fiber, which would cause tensile failure mode of CFRPs. Meanwhile, the delamination in low jet speed stages is larger than that in the high jet speed stages. These studies on the failure modes of CFRPs under LSC provide important basis for the future design of CFRP-based pyrotechnic separation devices, which is important to the lightweight design of launching vehicles

Trans-scale modeling framework for failure analysis of cryogenic composite tanks

The mechanical performances of cryogenic composite tanks need strict evaluation due to its extreme temperature condition of service. In this paper, a trans-scale modeling strategy is developed for the failure analysis of cryogenic composite structures, which is based on theories from micromechanics to continuum mechanics. Micromechanical model of representative volume element is developed to obtain the thermo-mechanical coupling properties of materials in the composite structure. Continuum mechanics model is sub-sequentially developed to predict the fields of physical properties in the composite structures. The predictions of performances of composite structures at cryogenic and different temperatures are of good agreement with conventional theoretical solutions. Numerical examples of cryogenic composite tanks indicate that the large temperature change can directly cause the fracture of matrix that can result in the overall failure of composite tanks. In addition, the thermal–mechanical coupling effect can reduce the prediction of critical thermal loads in the failure analysis of cryogenic composite tanks, which is more favorable for engineering designs due to the strict requirements of safety