Failure correlation reliability analysis of solid rocket motor grain based on polynomial chaos expansion

To address the issue that existing testing methods cannot achieve precise in situ characterization of the mechanical parameters of solid rocket motor grain materials, this work, based on the elastic contact theory, combines the generalized Maxwell model for viscoelastic materials to derive and establish the theoretical indentation model for the relaxation characteristics of propellant. Through a coordinated analysis of indentation relaxation testing and finite element simulations at different constant indentation depths, the applicability of the theoretical indentation model was studied. The results indicate that the relaxation modulus is highly consistent at different indentation depths, but there is a certain deviation between the indentation load–time simulation curve and the testing curve. This deviation increases as the constant indentation depth increases. Based on this, the causes of the theoretical indentation model error were analyzed, a correction method for the theoretical indentation model was proposed, and the modified theoretical indentation model was validated through a comparison of simulation and testing data. The theoretical indentation model provides a new method for the mechanical property testing and evaluation of solid rocket motor grain materials.

A detailed study of a set of combined acceleration methods is presented with the objective of accelerating the solid rocket motor grain burnback simulation based on the level set method. Relevant methods were improved by making use of unique characteristics of the grains, and graphical processing unit (GPU) parallelization is utilized to perform the computationally intensive operations. The presented flow traced the expansion of burning surfaces, and then Boolean operations were applied on the resulting surfaces to extract various geometric metrics. The initial signed distance field was built by an improved distance field generating method, and a highly optimized GPU kernel was used for estimating the gradient required by the level set method. An innovative Boolean operation method, thousands of times faster than ordinary ones, was ultimately proposed. Performance tests show that the overall speedup was close to 15 on desktop-class hardware, simulation results were proven to converge to analytical results, and the error boundary was 0.25%.

The structural integrity of the grain is very important for the grain with complex geometry. Large section column structure has its particularity, differs from that of a single column, its length to diameter ratio is large and absolute meat the increase of the thickness, particles of geometric shape and size of the key factors to determine the gas production rate and its change rule of the engine, at the same time, the engine thrust and pressure change with time, particle size determines the volume and weight of the combustion chamber,Therefore, the particle design of solid rocket motor determines the quality design index of the engine to a large extent.In order to improve the efficiency of model optimization, an agent model is established in this paper. The prediction accuracy of the model depends on the distance between prediction points and sample points. The shortest distance hierarchical clustering algorithm is used to improve the prediction accuracy.Through the research, the comprehensive effect of the key factors affecting the structural integrity of the propellant and the law of the influence on the structure and safety margin of the propellant are obtained. The research method and law can provide support for the large solid motor grain design, and provide theoretical reference for the solid rocket motor grain structure multi-parameter optimization design.

In solid propellant rocket motors, the design of grain port geometry primarily dictates the motor ballistic performance. The flexibility offered by the spatial variation of the port shape on motor performance is often discounted due to the requirement of complex mandrel shapes along with their associated manufacturing issues coupled with propellant processing constraints. Literature data indicate improvement in motor volumetric loading and stability by planned distribution of burn surface area along motor length. This paper deals with the realization and testing of a subscale motor with central finocyl-based grain geometry. A novel method of casting complex grain shapes in solid rocket motors using the wax mandrel technique is discussed. The wax mandrel preparation, propellant casting procedure, and wax mandrel removal setup are elaborated. Static testing results of the subscale motor with central finocyl port geometry are also presented as proof-of-concept. This work has demonstrated the feasibility of realizing solid rocket motor grains using the wax mandrel technique, which further enables realization of complex grain designs necessary to meet various mission requirements.

In order to determine the stress state of the solid rocket motor grain under the internal pressure load, based on the finite element numerical simulation calculation, the length and size requirements of the grain under the internal pressure simplified to a plane strain problem are obtained. Numerical simulation calculations are further carried out for the grains in plane strain state that meet the simplified conditions, and the radial and circumferential stress states of the grains are obtained. The numerical simulation results are compared with the viscoelastic theoretical solution of the grains under the same material parameters. The results show that when the aspect ratio exceeds 2.5, the axial strain is approximately 0, which can be equivalent to a plane strain problem. In addition, the analysis shows that under the action of internal pressure, the plane strain grains are in a bidirectional compression stress state with a radial and circumferential stress ratio of approximately 1:1. Finally, by comparing the numerical solution and the analytical solution, it is found that the relative error is within 3%, which verifies the correctness of the numerical simulation calculation results.

Aerospace design optimization using a compound repulsive particle swarm

A method for identifying the relaxation modulus or creep compliance of composite propellant based on indentation technique is proposed, which can rapidly and nondestructively measure the mechanical properties of solid rocket motor grain in storage. According to viscoelastic indentation theories, a constitutive model for conical indentation is derived to predict the mechanical parameters of composite propellants. The indentation test with different loading rates and the traditional tensile stress relaxation test for a certain PBT composite propellant were carried out to verify the feasibility of the proposed method. The results show that the prediction results calculated by the constitutive model are in good agreement with the load‐displacement curves of the indentation test, and the mechanical parameters identified by the constitutive model are similar to those parameters fitted by the tensile stress relaxation test. Relevant methods and conclusions can provide a reference for structural analysis and storage life prediction of solid rocket motors.

This paper addresses the prediction of solid propellant rocket motor grain failure under motor pressurisation on ignition loads at low temperature. In a previous study it was found that for slow cooldown loads use of a failure criterion based on strain energy gave good agreement with experimental results, but that for motor pressurisation on ignition at low temperature no criterion considered was found to give an accurate prediction of failure. Two failure criteria are now described which are found to give good agreement with experimental results. The first is a modified strain energy criterion based on a prediction of the behaviour of the failure envelope at high strain rates where material testing does not give reliable data. The second is based on a viscoplastic material characterisation using Extended Drucker-Prager plasticity models to derive rate dependant yield/failure envelopes in the plane of the first stress invariant, i.e. the pressure stress, and the second invariant of the deviatoric stress, i.e. the Von Mises stress.

Solid rocket motor (SRM) grains are critical propulsion components where internal defects can severely compromise performance and flight safety. Conventional X-ray film inspection suffers from low efficiency and accuracy, failing to meet modern production demands. This paper proposes an improved U-Net-based defect segmentation method for X-ray images. We first built an annotated dataset containing various real defects. To address U-Net’s limitations in small-defect segmentation, we integrated Squeeze-and-Excitation (SE) attention modules after its first five dual-convolution blocks, enhancing feature channel awareness. Experiments show our method outperforms standard U-Net, achieving 99.63% accuracy (vs. 99.56%) and 0.8513 IoU (vs. 0.8166), proving its effectiveness for SRM defect detection.

This work explores Solid Rocket Motor grain design, leveraging the possibilities offered by innovative additive manufacturing techniques based on slurry deposition and UV-curing. The primary objective is to create an automated design procedure capable of finding optimal solutions that match the specific mission requirements. This is achieved by exploiting new geometric and ballistic configurations that are attainable because of the absence of constraints imposed by the classical mix-cast-cure manufacturing process. The design optimization procedure is based on a stochastic optimization approach coupled with surrogate modeling of the grain pressure-time response at variation of geometrical and ballistic parameters. After automating the creation of geometric models and the computation of pressure-time routines to produce suitable databases, various surrogate models were tested. The selected surrogate model is then applied to evaluate different individuals in stochastic optimizer routines. The optimizer identifies the most suitable solution to obtain the desired pressure-time response and to meet the motor performance requirements. The results obtained show the ability of the procedures to automate the modified design process, handle novel design parameters, and obtain an adequate response to the expressed requirements.

Rocket motor grain consists of rigid particles embedded in a soft, rubbery matrix. The ingredients are chosen to maximize the burning properties, but when cracks develop during curing or storage, burn properties are altered. The present study was directed towards a study of the loss of the inverse square root singularity in the neighborhood where a crack intersects the free surface in simulated motor grain. Experiments were conducted on both cracked simulated pure binder and cracked simulated motor grain and algorithms were developed for computing fracture parameters from the data. Severe crack tip blunting prior to crack growth initiation was observed in the simulated motor grain which required a modification of the algorithm used for single phase materials. Efforts to determine the dominant eigenvalue after crack growth have met with limited success to date due to increasing data scatter.

In order to coordinate the many design parameters of the solid rocket motor (SRM) grain to get a better performance. A structure optimization method based on variation sketch and genetic optimization algorithm is proposed. Then by choosing a slotted-tube grain as the example, corresponding structure parameters optimization processes show the efficiency and convenience of this advanced structure optimization method. The objective function of SRM internal ballistics curves are converged after about 500 generations' evolution. The SRM internal ballistics curves comparison with initial one and optimized one also shows that the fluctuation range of the internal ballistics curve is reduced from about 20% to 8%. This is helpful to reduce the negative weight of SRM and improve its performance. It proves the accuracy of this grain design and optimization method.

Multidisciplinary Design and Optimization of Multistage Ground-launched Boost Phase Interceptor Using Hybrid Search Algorithm

This study is aimed at the stability and effect of the crack groups in the solid rocket motor (SRM) grain when it was launched at normal temperature. Based on the nearly incompressible viscoelastic finite element method, several cracks were preset in a critical location along with the dangerous point of the back slot. The singular crack elements at the tips of crack groups were established to calculate the J -integral. With the position of the cracks, the J -integral of the various crack tips was, respectively, calculated to prejudge its stability and the group effect. Finally, the experimental measured critical J -integral J IC was compared with the numerical simulation result. The results showed that in the collinear crack groups, the enhancement effect of the main crack was caused by the nearest second crack, and the significant shielding effect of the main crack was occurred in the noncollinear crack groups. Moreover, the experimental result showed that the numerical method had high accuracy.

Fatigue crack propagation analysis in structures with random parameters based on polynomial chaos expansion method