1.Goals

• Identify shock wave propagation characteristics on honeycomb structure with various joints.

2. Approaches

• Laser Doppler velocimetry (LDV) is used.
• Various joint such as corner joint, butt joint, T-shape joint is made.
• Shock Response Spectrum(SRS) is used to quantity magnitude of shock.
• Attenuation of shock can be identified by measuring before and after joint.

• ANSYS Workbench Explicit Dynamics and ANSYS AUTODYN are used
• Maximum mesh aspect ratio is considered to reduce the calculation time.
• Analytical results and experimental results are compared.
• The parametric study is conducted using finite element analysis method.

3. Research Achievements

• Insert was installed on honeycomb sandwich panel.
• Honeycomb panel with insert and plate was bolted.
• Measuring before and after joint, attenuation factor of insert system was identified.

3. Recent Achievements

• Much efficient (inducing less stress and requiring less force) folding methodology is developed for the Yoshimura cylinder.
• The effectiveness of the proposed folding methodology is confirmed through the static analysis using ANSYS.
• This folding methodology could be a foundation for the 3-D deployable structure with Yoshimura pattern.

• Analysis on honeycomb & plate joint structure was conducted.
• Analysis results are verified by comparing with experimental results.
• Parametric study can be conducted using verified analysis method.

1.Goals

• Establishment of the mathematical model which can describe the dynamic separation mechanisms with low computational resources and short time.
• Identify the separation behaviors using numerical analysis method (ANSYS AUTODYN).

2. Approaches

• Separation procedure can be divided into several stages based on mechanical event sequence of components.
• Each stage is governed by different simultaneous differential equations containing equations of motion and combustion equations.
• Saint Robert’s Law is used as a combustion model of zirconium potassium perchlorate (ZPP) charge.
• Friction model, O-ring model, bolt deformation model is considered for accurate simulation.
• To simulate this mathematical model, the MATLAB function ODE45 is used for the calculation of simultaneous differential equations.

• Design 3D model of the separation device by Solidworks.
• Export geometry to explicit analysis and generate mesh.
• Setup the boundary conditions for analysis.
• Simulate and identify the separation dynamics of the components.

• 3-D separation behavior analysis is performed
• Every contact condition is assumed to linear contact such as bonded or no separation
• Maximum mesh aspect ratio is considered to reduce the calculation time.
• Pretension load and deformation are applied by static structural analysis.

• Separation procedure is divided into five stages based on mechanical event of those parts.
• Each stage is governed by different simultaneous differential equations containing equations of motion and combustion equations.
• Saint Robert’s Law is applied as combustion model of ZPP propellant.
• To simulate this mathematical model, the MATLAB function ODE45 is used for the calculation of simultaneous differential equations.

3. Research Achievements

• For several main design parameters, effects of each parameter on the separation performances are figured out in variance of ±20%.

• Validation by comparing the separation time with the experiment result.
• SEA is employed to analyze the propagated shock due to triggering of explosive bolt
• Detail separation procedure is identified from dynamic characteristics of internal parts.

• Parameter study on the coefficient of friction is conducted
• Analysis results are verified by comparing separation time with AUTODYN simulation results.

1.Goals

• Separation behavior analysis of Ridge-Cut explosive bolts for evaluate separation success rate without experiments and improve reliability of separation by design modification.
• Complex separation phenomena and characteristics of Ridge-Cut explosive bolts are understood by using separation behavior analysis.

2. Approaches

• 2-D Axisymmetric behavior analyses are mainly performed.
• Each stage is governed by different simultaneous differential equations containing equations of motion and combustion equations.
• An explosive bolt body is modeled using 0.2 mm Lagrange elements, Shock Equation of States (EOS), Johnson-Cook Strength model, Principal Stress Failure model and Geometric Strain (Instantaneous) Erosion Model.
• Modeling of PETN and RDX is done using 0.1 mm Euler elements and JWL EOS.
• Air is modeled using 0.1 mm Euler elements and Ideal Gas EOS.
• Ridge-Cut Mechanism (also known as spalling) by which Ridge-Cut explosive bolts are separated can be observed in the analysis.

3. Recent Achievements

• Validation by comparing with experiments.
• The best prediction of the experimental results is obtained when 2.8×10^6 kPa critical value of normal tensile stress is used.
• Ridge-Cut Mechanism is observed.

• Some design guidelines about fixtures are suggested.
• For more information, Refer Lee, J.-H., Han, J.-H., Lee, Y.-J., and Lee, H.-J., “Separation Characteristics Study of Ridge-Cut Explosive Bolts”, Aerospace Science and Technology, Vol. 39, pp. 153-168, Dec. 2014. [DOI].

1.Goals

• Predict the response of the subsystem of missile subjected to high frequency load due to activation of explosive bolt for stage separation
• Study the effect of several assumed loss factor and contrast it with the experimental results

2. Approaches

• Define System (dividing into different subsystem, defining relationship between them)
• Evaluate parameters like loss factor, mode count etc.
• Calculate response (frequency band averaged FRF magnitude)

• Assume virtual modes in which synthesized FRF approximates the frequency band averaged FRF magnitude.
• Using synthesized FRF, calculate response in frequency domain.
• Inverse Fourier transform to get time signal
• Use the time signal to obtain SRS

3. Recent Achievements

• Behavior analysis of explosive bolt is performed using Ansys-Explicit Dynamics/AUTODYN
• SEA is employed to analyze the propagated shock due to triggering of explosive bolt
• For more information, Refer “Marshal Deep Kafle, Dae-Oen Lee, Juho Lee, Sung-Hyun Woo, Jae-Hung Han, “Numerical Modeling of Shock Generation and Propagation during Satellite Separation”, Advances in Aircraft and Spacecraft Science, Submitted.”

• Three plate connected in series is analyzed using EFM with built in MSC/Nastran solver
• SEA analysis is also performed and compared with EFM analysis
• For more information, Refer “Marshal Deep Kafle, Dae-Oen Lee, Sung-Hyun Woo, Jae-Hung Han, “Shock Response Estimation by Energy Flow Method and Virtual Mode Synthesis”, ICSV20, Bangkok, Thailand, July 7~11, 2013.”

• Missile body with 11 subsystems is modeled and the response is measured in each of them
• Several assumed loss factors are used to model the system and SEA predicted results are compared with the experimental results

1.Goals

• Develop a new three-axis hybrid mesh isolator using the pseudoelasticity of a shape memory alloy wire that was manufactured and tested to attenuate pyroshock and vibration transmitted to the electronic components.

2. Approaches

• Knitting : Manufacturing wire mesh using knitting machine with a continuous wire
• Cut & Fold over : Wire mesh is cut and folded over before inserting to the press machine
• Insert: Insert folded wire mesh to the designed press mold
• Pressing : Pressing folded wire mesh with a designed pressure
• Inspection

• To characterize the isolation capability, quasi-static loading tests were performed.
• The ground pyroshock tests are performed.
• Random vibration tests are performed.
• The healthiness of the hybrid mesh isolator was also studied.

3. Recent Achievements

• To characterize the isolation capability, quasi-static loading tests were performed; the test results showed that the pseudoelastic effect of the shape memory alloy wire significantly absorbs energy due to the stress-induced phase transformation.
• The ground pyroshock test results showed a remarkable pyroshock load attenuation of the hybrid mesh isolator in all frequency ranges.
• The dynamic characteristics and vibration isolation performances of the mesh isolators were also verified by random vibration tests.
• The healthiness of the hybrid mesh isolator was also studied under a harsh vibration loading level, and the results confirmed its wide applicability without degradation of the isolation capability.
• For more information, Refer “Youn, S.-H., Jang, Y.-S., and Han, J.-H., “Development of a three-axis hybrid mesh isolator using the pseudoelasticity of a shape memory alloy,” Smart Materials and Structures, Vol. 20, No. 7, pp.1-12, June, 2011.”

1.Goals

• Develop a novel frequency tunable isolator based on shape memory alloy for effective shock and vibration suppression. If the natural frequency of the isolator can be controlled by changing the stiffness of the resilient material when an excitation frequency approaches the designed natural frequency of the isolator, the structural integrity can be ensured by preventing the amplification of the vibration.

2. Approaches

• Knitting : Manufacturing wire mesh using knitting machine with a continuous wire.
• Cut & Fold over : Wire mesh is cut and folded over before inserting to the press machine
• Insert: Insert folded wire mesh to the designed press mold
• Pressing : Pressing folded wire mesh with a designed pressure
• Inspection

• Bottom plate is connected with the vibration source.
• isolation materials are arranged between a vibrating source and an object.
• The SMA wire actuators connected between top and bottom plates and contracted at an Af -Austenite finish temperature.
• The recovery spring coiled around an outer of the isolation material.

• Natural frequencies test of the system with various compressive deformations.
• Random vibration tests are performed.
• WI Compressive load tests are performed.
• Phase transformation temperatures tests are performed.
• The tensile test at room temperature are performed.
• Recovery stress tests are performed.
• Frequency tuning testsare performed.
• Pyroshock tests are performed.

3. Recent Achievements

• The compressed mesh washer isolator (WI) using the pseudoelasticity of the SMA was manufactured and tested: The stiffness change of WI can be easily achieved using a small compressive displacement.
• A concept of frequency tunable isolator was introduced: The resonant frequency of the proposed isolator is selectively controlled in two Modes. In Mode 1, the isolator has a lower natural frequency than in Mode 2. However, in Mode 2, the isolator has a higher natural frequency than in Mode 1.
• The frequency tunable shock isolator for launch vehicle was developed in order to achieve both shock attenuation performance and avoidance of the vibration amplification.
• The detailed design processwas introduced: The vibration characteristics of the WI and compressive load were observed through a random vibration test with compressive deformation.