Search

Electronic components assembled in satellites should be able to withstand the vibration, noise, and impact loads generated by space vehicles during launch. To simulate the impact loading in a laboratory environment, a pyroshock test simulates an impact load resulting from explosions during the stage and pairing separation of launch vehicles, which imposes significant stress on the components, potentially leading to failures and damage. To ensure component reliability before the flight model (FM) stage, where components are mounted on the actual launch vehicle and sent into orbit, a pyroshock test is conducted during the qualification model (QM) stage using identical parts and specifications. This process involves measurements of the acceleration induced by pyroshock to calculate the shock response spectrum (SRS) and evaluate the components' reliability against the required SRS to confirm their ability to endure the shock and operate normally in post-tests. The aerospace developer determines the SRS requirements based on the space launch vehicle and the installation location of the electronic components. Configuring a suitable pyroshock test to meet these requirements typically involves extensive trial and error. This study aims to minimize such trial and error by examination of SRS changes through a numerical approach by table structural vibration analysis. The structure is subjected to in-plane impacts using a steel ball via a pendulum method. Various SRS profiles are calculated by test factors such as the weight of the steel ball, the pendulum angle, and the installation position of the test specimen. Furthermore, a genetic algorithm is utilized to derive the optimal test conditions that satisfy the required SRS. An automated pyroshock test system is developed to enhance repeatability and reduce human errors. [ABSTRACT FROM AUTHOR]

This research paper proposes a unique way to safeguard delicate systems on submerged platforms from the undesirable effects of underwater explosion shock loads. The underwater detonation of an explosive charge and mines produce devastating underwater shocks against underwater platforms. Shock load developed underwater has been analyzed, and a shock response spectrum (SRS) approach to compute shock peak responses has been adopted. SRS shock absorption frequency satisfies requirements for both shock absorption and delicate systems. The shock load was reduced to 2g by altering the delicate system stiffness and damping properties. The analytical model for a single DOF system was formulated, and simulation was carried out using ANSYS solver. The stiffness has been spread across various points along the length of the delicate system, allowing it to undergo translational oscillations when subjected to shock loads. This research paper presents an innovative design approach for a shock absorption system intended for underwater sensitive objects, emphasizing simplicity, distinctiveness, compactness, reliability, and electromagnetic compatibility. Experimental testing validated the shock absorption design on the prototype. Shock testing determined the absorber's maximum displacement and sensitive object acceleration. [ABSTRACT FROM AUTHOR]

Electronic components assembled in satellites should be able to withstand the vibration, noise, and impact loads generated by space vehicles during launch. To simulate the impact loading in a laboratory environment, a pyroshock test simulates an impact load resulting from explosions during the stage and pairing separation of launch vehicles, which imposes significant stress on the components, potentially leading to failures and damage. To ensure component reliability before the flight model (FM) stage, where components are mounted on the actual launch vehicle and sent into orbit, a pyroshock test is conducted during the qualification model (QM) stage using identical parts and specifications. This process involves measurements of the acceleration induced by pyroshock to calculate the shock response spectrum (SRS) and evaluate the components’ reliability against the required SRS to confirm their ability to endure the shock and operate normally in post-tests. The aerospace developer determines the SRS requirements based on the space launch vehicle and the installation location of the electronic components. Configuring a suitable pyroshock test to meet these requirements typically involves extensive trial and error. This study aims to minimize such trial and error by examination of SRS changes through a numerical approach by table structural vibration analysis. The structure is subjected to in-plane impacts using a steel ball via a pendulum method. Various SRS profiles are calculated by test factors such as the weight of the steel ball, the pendulum angle, and the installation position of the test specimen. Furthermore, a genetic algorithm is utilized to derive the optimal test conditions that satisfy the required SRS. An automated pyroshock test system is developed to enhance repeatability and reduce human errors.

The shock loads generated by spacecraft during docking can cause functional failure and structural damage to aerospace electronic equipment and even lead to catastrophic flight accidents. There is currently a lack of systematic and comprehensive research on the shock environment of spacecraft electronic equipment due to the diversity and complexity of the shock environment. In this paper, the validity of the finite element model is verified based on the sinusoidal vibration experiment results of the spacecraft reentry capsule. The method of shock dynamic response analysis is used to obtain the shock environment of electronic equipment under different shock loads. The shock response spectrum is used to describe the shock environment of aerospace electronic equipment. The results show that the resonance frequency error between the sinusoidal vibration experiment and the model is less than 4.06%. When the docking relative speed of the reentry capsule is 2 m/s, the shock response spectrum values of one of the equipment are 30 m2/s, 0.67 m/s, and 0.059 m, respectively. The wire rope spring on the mating surface can provide vibration isolation and shock resistance. An increase in spring damping coefficient results in a decrease in the amplitude and time of the vibration generated. An increase in spring stiffness reduces the input of shock load within a certain range. These research results can provide guidance for the design and evaluation of shock environmental adaptability of aerospace electronic equipment. [ABSTRACT FROM AUTHOR]

To overcome the limitations of the hybrid tractor bumping tests, which include extended cycle times, high costs, and impracticality for single-part reliability verification, this study focuses on the exhaust system mounting bracket of a hybrid tractor. A novel approach that combines multi-objective particle swarm optimization (MOPSO) and wavelet decomposition algorithms was employed to enhance the reconstruction of shock vibration signals. This approach aims to enable the efficient acquisition of input signals for subsequent shaker table testing. The methodology involves a systematic evaluation of the spectral correlation between the original signal and the reconstructed signal at the stent's response position, along with signal compression time. These parameters collectively constitute the objective function. The multi-objective particle swarm optimization algorithm is then deployed to explore a range of crucial parameters, including wavelet basic functions, the number of wavelet decomposition layers, and the selection of wavelet components. This exhaustive exploration identifies an optimized signal reconstruction method that accurately represents shock vibration loads. Upon rigorous screening based on our defined objectives, the optimal solution vector was determined, which includes the utilization of the dB10 wavelet basic function, employing a 12-layer wavelet decomposition, and selecting wavelet components a12 and d3~d11. This specific configuration enables the retention of 95% of the damage coefficients while significantly compressing the test time to just 46% of the original signal duration. The implications of our findings are substantial as the reconstructed signal obtained through our optimized approach can be readily applied to shaker excitation. This innovation results in a notable reduction in test cycle time and associated costs, making it particularly valuable for engineering applications, especially in tractor design and testing. [ABSTRACT FROM AUTHOR]

Shock vibration environments frequently occur and threaten the reliability of products in aerospace engineering. This work deals with the shock response spectra replication control method for multi-shaker vibration test systems. Two synthetic methods for reconstitution of shock response signals with specified shock response spectra are presented. One is the random delay superposition method and the other is the filtering superposition method. The former utilizes a random time delay vector satisfying a normal distribution to simulate a shock response signal with symmetrical attenuated oscillation features while the latter is employed when the measured shock records are available. A time-domain inverse system method is formulated to obtain the multi-input drive signals based on a finite-difference equation. The multi-input multi-output frequency response functions are estimated first and then used to construct the inverse system. The multi-output shock response spectra are calculated by response signals from control sensors. A closed-loop iteration control procedure is provided to correct the drive signals according to the deviations between the responses and corresponding reference values. A numerical simulation and a triaxial vibration test are carried out and the results show the feasibility and effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Featured Application: In this work, the transient response of a single-degree-of-freedom (SDOF) system with a tubular linear eddy current damper (TLECD) under shock excitation is calculated and analyzed. Moreover, to achieve the best design and performance assessment of the structural shock vibration control by the TLECD, this study introduces the shock response spectrums (SRSs) and a straightforward design flowchart of the TLECD for its mechanical characteristics. The nonlinear dynamic characteristic of a tubular linear eddy current damper (TLECD) and the transient responses to shock excitations of a single-degree-of-freedom (SDOF) system with the TLECD are studied. First, the nonlinear force-velocity relationship of the TLECD is discussed using the finite element simulation and mathematical model fitting. Next, the influences of three forms of shock excitation and various mechanical parameters of the TLECD on shock vibration control of an SDOF system with the TLECD are investigated. Moreover, for the SDOF systems with the TLECD or the nonlinear fluid viscous dampers (FVD) at the same maximum displacement and maximum damper force, the time to reach the maximum displacement, the time to reach one-third of the maximum displacement, the energy input of the external loading, and the energy dissipation of dampers are analyzed and compared. Finally, the shock response spectrums (SRSs) of the SDOF system and the design flowchart for the TLECD are presented to provide a reference for shock vibration control of the SDOF system with the nonlinear TLECD and the design of TLECDs. The results show that there is an optimal dimensionless critical relative velocity that minimizes the dimensionless maximum damping force for reaching the target maximum displacement, and compared to the FVD, the TLECD greatly shortens the time to reach one-third of the maximum displacement. [ABSTRACT FROM AUTHOR]

This paper reviews prominent published works on UNDEX phenomenon and associated load characterization on structures subjected to UNDEX. An overview of characteristic events associated with UNDEX phenomenon resulting in a transient dynamic loading on the structure has been presented. A load characterization methodology for far-field UNDEX, based on empirical calculation of incident pressure load time history on the structure due to an explosive charge of known weight and standoff distance. The presented UNDEX load characterization includes the effect of FSI based on Taylor's theory for the estimation of the modified transient pressure filed. Salient features in numerical modelling and simulations of non-linear structural responses and dynamic effects due to UNDEX have been highlighted. Significance of zoning from design against shock for shipboard equipment and scope of FEA numerical simulations using a high performance computing (HPC) setup for validation of loads corresponding to a given shock grade/standard, and its importance in optimizing platform designs against shock hardening requirements, have also been discussed briefly. [ABSTRACT FROM AUTHOR]

We propose an alternative method for processing infrared thermography (IRT) data based on a thermal 1-layer model. The method is based on the analogy of the Shock Response Spectrum (SRS) analysis for mechanical systems (ISO 18431). A thermal Q-factor, similar to the resonance sharpness (Q-factor) of a mechanical oscillator, is introduced as a parameter for selecting a specific thermal 1-layer model. Two main aspects of this method and corresponding properties have been considered: the strictly model-based treatment of this methodology and an empirical introduction of additional bandpass filters. The method is validated with two practical examples: for a homogeneous polymer sheet with blind holes and an inhomogeneous plate made of carbon fiber reinforced polymer (CFRP) with artificial defects, the capability of defect detection is compared with established methods. The comparison of the results with the commonly used data processing methods of IRT as Pulsed Phase Thermography (PPT) and Modified Differential Absolute Contrast (MDAC) shows equivalent or sometimes improved performance. [ABSTRACT FROM AUTHOR]

To overcome the limitations of the hybrid tractor bumping tests, which include extended cycle times, high costs, and impracticality for single-part reliability verification, this study focuses on the exhaust system mounting bracket of a hybrid tractor. A novel approach that combines multi-objective particle swarm optimization (MOPSO) and wavelet decomposition algorithms was employed to enhance the reconstruction of shock vibration signals. This approach aims to enable the efficient acquisition of input signals for subsequent shaker table testing. The methodology involves a systematic evaluation of the spectral correlation between the original signal and the reconstructed signal at the stent’s response position, along with signal compression time. These parameters collectively constitute the objective function. The multi-objective particle swarm optimization algorithm is then deployed to explore a range of crucial parameters, including wavelet basic functions, the number of wavelet decomposition layers, and the selection of wavelet components. This exhaustive exploration identifies an optimized signal reconstruction method that accurately represents shock vibration loads. Upon rigorous screening based on our defined objectives, the optimal solution vector was determined, which includes the utilization of the dB10 wavelet basic function, employing a 12-layer wavelet decomposition, and selecting wavelet components a12 and d3~d11. This specific configuration enables the retention of 95% of the damage coefficients while significantly compressing the test time to just 46% of the original signal duration. The implications of our findings are substantial as the reconstructed signal obtained through our optimized approach can be readily applied to shaker excitation. This innovation results in a notable reduction in test cycle time and associated costs, making it particularly valuable for engineering applications, especially in tractor design and testing.

Aiming at a design for buffering and load reduction configuration for a large-scale (diameter greater than 500 mm) vehicle entering water at high speed (greater than 100 m/s), a numerical model for a vehicle entering water at high speed was employed based on an arbitrary Lagrange-Euler (ALE) algorithm. Combined with modal analysis and shock response spectrum, the influence of the head cap on the dynamic characteristics of the structure was analyzed. The results showed that the peak value and pulse width of the impact load on the vehicle increased with the increase in the speed of water entry. The existence of the head cap increased the complexity of the forces on the vehicle during the process of water entry. The initial formation of the cavity was greatly affected by the head cap. The head cap and the vehicle separated in the later stage of the water entry. During the process of water entry, the shell of the vehicle was mainly compressed and bent and the head cap reduced the deformation. The relevant conclusions of this paper can provide some input for the design of a new buffering structure and vehicle shell. [ABSTRACT FROM AUTHOR]

Low-frequency errors are a type of testing errors commonly existing in pyroshock experiments due to the harsh mechanical environment that lead to inaccuracy and contamination of pyroshock data. It is necessary to eliminate such low-frequency errors from pyroshock data via data analysis. Two methods based on discrete wavelet transform (DWT) and ensemble empirical mode decomposition (EEMD) are proposed, respectively, in this article. Firstly, the principle and operating process of these two methods are introduced, where four correlation coefficients are defined to determine the decomposition level for quantitative correction. Then, the two methods are applied to remove the integral zero shift from a set of pyroshock test data, respectively, and the capability and effectiveness of the two methods are compared. It is revealed from the comparison studies that both methods are capable of removing integral zero shift effectively to correct the shock response spectrum and improve the accuracy of pyroshock data. The correlation coefficients constructed here can help to realize quantitative selection of key parameters for the two methods. The DWT method shows better correction performance for extracting accurate parameters, whereas the EEMD method is more concise and convenient for application. [ABSTRACT FROM AUTHOR]

Vibrations and shocks are found among mechanical phenomena undergone by packaging systems. In order to verify the behaviour of packaging systems under shocks, test protocols advocate the execution of drop tests, inclined plane tests, forklift handling courses and so on in laboratories. Nevertheless, even if these protocols are efficient, they do not replicate the wide variety of transient events occurring during transportation. That is why there is a need in developing a method capable of replicating actual transient events in a reproductive way in laboratories. This work concerns the comparison of the responses of a packaging system subjected to two different simulations of the same transient event with the aim to forward develop specifications. The definition and elaboration of shock response spectra (SRS) are reviewed in the first part of this work. Afterwards, a data acquisition enables the recording of classical transient events generated by a forklift. Then the calculation of the SRS of one of those transient events enables the generation of a time signal different from the transient event recorded. Finally, a comparison between the response of a packaging system subjected to the time transient event as it is recorded and the response to the time transient event calculated from the SRS is carried out. The first results based on the study of autocorrelation functions, intercorrelation functions, energy spectral densities (ESDs) and damage calculation conclude towards an equivalence between a real‐time replication and an SRS simulation in the case of one transient event and one packaging system. [ABSTRACT FROM AUTHOR]

• Shock fatigue damage failure boundary for BGA solder joints based on SRS is proposed. • Cumulative damage criteria and statistical characteristics of life are considered. • Bayesian estimation method based on the Bootstrap approach is proposed. Multiple shock damage failure of ball grid array (BGA) solder joints is one of the important reasons for reusable spacecraft mission failure. Shock fatigue damage failure boundary of BGA solder joints is proposed based on shock response spectrum (SRS), which can be used to assess the damage failure state. Weibull distribution is employed to characterize the shock fatigue life for a specified SRS. A Bayesian estimation method based on the Bootstrap approach is proposed to estimate Weibull distribution parameters. By using the time-domain load synthesized method based on wavelet and the experimentally validated shock fatigue life model, the shock fatigue life data of BGA solder joints corresponding to different SRS are extended. The variation patterns of the scale and shape parameters with the SRS parameters is analyzed. Then the shock fatigue damage failure boundary based on SRS is determined for a given design life and reliability. The results show that the critical SRS amplitude increase with the rise of the inflection point frequency and the low-frequency slope, respectively. The developed method is expected to provide references for the environment-adaptive design of BGA solder joints in reusable spacecraft. [ABSTRACT FROM AUTHOR]

The nonlinear dynamic characteristic of a tubular linear eddy current damper (TLECD) and the transient responses to shock excitations of a single-degree-of-freedom (SDOF) system with the TLECD are studied. First, the nonlinear force-velocity relationship of the TLECD is discussed using the finite element simulation and mathematical model fitting. Next, the influences of three forms of shock excitation and various mechanical parameters of the TLECD on shock vibration control of an SDOF system with the TLECD are investigated. Moreover, for the SDOF systems with the TLECD or the nonlinear fluid viscous dampers (FVD) at the same maximum displacement and maximum damper force, the time to reach the maximum displacement, the time to reach one-third of the maximum displacement, the energy input of the external loading, and the energy dissipation of dampers are analyzed and compared. Finally, the shock response spectrums (SRSs) of the SDOF system and the design flowchart for the TLECD are presented to provide a reference for shock vibration control of the SDOF system with the nonlinear TLECD and the design of TLECDs. The results show that there is an optimal dimensionless critical relative velocity that minimizes the dimensionless maximum damping force for reaching the target maximum displacement, and compared to the FVD, the TLECD greatly shortens the time to reach one-third of the maximum displacement.

The purpose of this study was to determine the effect of fatigue on impact shock wave attenuation and assess how human biomechanics relate to shock attenuation during running. In this paper, we propose a new methodology for the analysis of shock events occurring during the proposed experimental procedure. Our approach is based on the Shock Response Spectrum (SRS), which is a frequency-based function that is used to indicate the magnitude of vibration due to a shock or a transient event. Five high level CrossFit athletes who ran at least three times per week and who were free from musculoskeletal injury volunteered to take part in this study. Two Micromachined Microelectromechanical Systems (MEMS) accelerometers (RunScribe®, San Francisco, CA, USA) were used for this experiment. The two RunScribe pods were mounted on top of the foot in the shoelaces. All five athletes performed three maximum intensity runs: the 1st run was performed after a brief warmup with no prior exercise, then the 2nd and the 3rd run were performed in a fatigued state. Prior to the 2nd and the 3rd run, the athletes were asked to perform at maximum intensity for two minutes on an Assault AirBike to tire them. For all five athletes, there was a direct correlation between fatigue and an increase in the aggressiveness of the SRS. We noticed that for all five athletes for the 3rd run the average SRS peaks were significantly higher than for the 1st run and 2nd run (p < 0.01) at the same natural frequency of the athlete. This confirms our hypothesis that fatigue causes a decrease in the shock attenuation capacity of the musculoskeletal system thus potentially involving a higher risk of overuse injury. [ABSTRACT FROM AUTHOR]

The piezoresistive pressure sensor is a widely used electronic component whose accuracy and function are strongly affected by the external mechanical environment. This paper studies the failure mode and damage boundary of piezoresistive pressure sensors under shock load. The failure mode of the pressure-sensitive elastic plate (the kernel structure of the pressure sensor) is derived based on the thin-plate theory. The damage boundary of the piezoresistive pressure sensor is obtained by analyzing the experiment and numerical simulation results, which agree well with the theoretical analysis. Results prove that the damage boundary of the piezoresistive pressure sensor is governed by the pseudo-velocity shock response spectrum (PVSRS) of the shock environment, which is about 7 m/s for the specimen in this paper. This study can provide guidelines for the adaptability design of electronic components. • The plate model is suitable for analyzing the shock damage mechanism of the pressure-sensitive component. • High stress induced by the solid-gel collision is the main reason of shock damage of the pressure-sensitive plate. • The PVSRS of the shock environment governs the damage boundary of the pressure-sensitive plate. • The critical value of the PVSRS causing failure on the pressure sensor is 6 m/s∼7 m/s. [ABSTRACT FROM AUTHOR]

Nut fasteners are produced by machines working around the clock. Companies generally operate with a run-to-failure or planned maintenance approach. Even with a planned maintenance schedule, however, undetected damage to the dies and non-die parts occurring between maintenance periods can cause considerable downtime and pervasive damage to the machine. To address this shortcoming, force data from the fourth and sixth dies of a six-die nut manufacturing machine were analysed using correlation to the best health condition on the force profile and on the force shock response spectrum profile. Fault features such as quality adjustments and damage to both die and non-die parts were detectable prior to required maintenance or machine failure. This detection was facilitated by the determination of health thresholds, whereby the force SRS profile generated a longer warning period prior to failure. The analytical approach could benefit the industry by identifying damage that would normally go undetected by operators, thereby reducing downtime, extending die life, enabling "as needed" maintenance, and optimising machine operation. [ABSTRACT FROM AUTHOR]

Deep space exploration technology is an important development direction for scientific exploration. The penetrator method has been proposed as an inexpensive method of studying planetary bodies. The basic principle of this method is that the detection equipment carried by the high-speed penetrator hits a planetary body at a high speed and is buried up to several meters below the surface to carry out detection work. During the frictional collision process with the planets crust, the instantaneous acceleration peaks of the scientific payload (electronic instrumentation) are large. Shock protection of these payloads is necessary to improve their survival and mission success. In this paper, with the goal of improving the survival rate of scientific loads inside a penetrator, a penetrator with a multilayer energy-absorbing structure is developed, in which cushioning protection measures, such as an aluminum foam-filled corrugated tube(AFFT) structure, polyurethane rubber, and epoxy resin potting, are applied to the penetrator. Since the analysis of this process is a highly nonlinear problem, a numerical modeling method is the main approach in this paper. The LS-DYNA software platform was used to simulate the penetrators penetration process on a moon soil medium. The results obtained using empirical formulas and theoretical derivations were compared with the results of numerical analysis to ensure the accuracy of the penetration simulation model. The finite element model of the penetrator was then verified and modified by conducting shock response spectral experiments and shock simulations. The results showed that the spacer scheme had a positive effect on the impact isolation and energy absorption. In addition, this scheme provides an important reference for the design of the penetrator prototype to guarantee the success of subsequent ground rocket sled experiments. • The buffering and energy absorption characteristics of the proposed AFFT structure are analyzed applied to the penetrator. • Through numerical simulation of the penetration process, the initial velocity satisfying the penetration depth was obtained. • The impact response spectrum test and simulation analysis of the penetrator prototype have verified the numerical model. [ABSTRACT FROM AUTHOR]

An improved method based on the Hybrid Finite Element-Statistical Energy Analysis (FE-SEA) method and quasi-steady state theory is proposed to predict the response of spacecraft structure during the process of pyrotechnics separation. Firstly, the amplitude–frequency value of shock load is obtained by using time-frequency conversion technology. Then, according to the frequency response characteristics of each part of the spacecraft structure, a more accurate hybrid FE-SEA model is established. The piecewise loading method is used to predict the response of the hybrid model. Finally, the time domain response results are reconstructed, and the shock response spectrum (SRS) is calculated. Based on the test system of simulating pyroshock, the shock experiment of spacecraft structure is conducted. The high frequency and high velocity character of pyroshock could be effectively simulated, and an accurate shock force function could be obtained through the experiment. This indicates that the numerical results are in line with the ones of the experiment. The SRS obtained from experiments and calculations have similar trends and amplitudes. This conclusion verifies the rationality and sufficient accuracy of the novel method in this paper. The novel method presented in this paper greatly improves the computational efficiency. At the same time, it provides theoretical guidance for shock response prediction of spacecraft structure by steady-state methods. [ABSTRACT FROM AUTHOR]

Aiming at a design for buffering and load reduction configuration for a large-scale (diameter greater than 500 mm) vehicle entering water at high speed (greater than 100 m/s), a numerical model for a vehicle entering water at high speed was employed based on an arbitrary Lagrange-Euler (ALE) algorithm. Combined with modal analysis and shock response spectrum, the influence of the head cap on the dynamic characteristics of the structure was analyzed. The results showed that the peak value and pulse width of the impact load on the vehicle increased with the increase in the speed of water entry. The existence of the head cap increased the complexity of the forces on the vehicle during the process of water entry. The initial formation of the cavity was greatly affected by the head cap. The head cap and the vehicle separated in the later stage of the water entry. During the process of water entry, the shell of the vehicle was mainly compressed and bent and the head cap reduced the deformation. The relevant conclusions of this paper can provide some input for the design of a new buffering structure and vehicle shell.

This paper presents an analysis of the correlation between setback and high-impact test loadings using the shock response spectrum (SRS). The modal analysis of the electronic assembly structure is implemented to determine the frequency range for the SRS analysis. A preliminary test of the high-impact tester is conducted with a reference impact velocity. Based on experimental data, finite element (FE) simulation is employed to predict the acceleration states at different impact velocities. The acceleration curves generated from FE simulation are included in the shock response spectrum for the correlation analysis. A proposed impact velocity is expected to cause a similar damage to the electronic assembly structure. This study provides valuable insight into the relationship between setback and high-impact test loadings, as well as a method for predicting and evaluating the potential damage to electronic assembly structures during high-impact testing. [ABSTRACT FROM AUTHOR]

The shock response spectrum (SRS) applied to pyroshock designs and tests for space systems does not include input acceleration time history; therefore, it cannot be used directly in structural nonlinear dynamic analysis before acceleration time history is synthesized. Existing synthesis methods typically rely on certain experimental data. In this study, a combined method for pyroshock acceleration synthesis is presented using a series of wavelets at low frequencies and damped sines at medium-high frequencies in the absence of experimental data. To improve the quality of the synthesized SRS, we develop an improved adaptive genetic algorithm (IAGA) with nonlinear adaptive adjustments of crossover and mutation probabilities. Numerical tests show that combined with the developed IAGA, the new method achieves higher accuracy and practicability in the synthesis of pyroshock acceleration compared with traditional methods. This work is expected to improve the calculation accuracy of spacecraft structure response under pyroshock loads.

This paper presents an approximate computing method of a shock response spectrum induced by a drop-weight shock test. The proposed method is based on a reduced impedance method, and computes the shock response spectrum by synthesizing the vibration characteristics of the spacecraft equipment and shock test device. A computational efficiency of the traditional reduced impedance method is significantly improved by proposing the method to only synthesize the dominated vibration characteristics of the substructures. The shock responses on the simplified model of the drop-weight shock test device are analyzed by the traditional reduced impedance method and the proposed method. Then, the shock response spectra given by both methods are compared. The result shows that the proposed method provides the shock response spectrum with accuracy of ±6dB for the traditional methods, and the computation cost is decreased by 1/60. This study offers a practicable approach to estimate an approximate shock response spectrum before a drop-weight shock test.

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The purpose of this study was to determine the effect of fatigue on impact shock wave attenuation and assess how human biomechanics relate to shock attenuation during running. In this paper, we propose a new methodology for the analysis of shock events occurring during the proposed experimental procedure. Our approach is based on the Shock Response Spectrum (SRS), which is a frequency-based function that is used to indicate the magnitude of vibration due to a shock or a transient event. Five high level CrossFit athletes who ran at least three times per week and who were free from musculoskeletal injury volunteered to take part in this study. Two Micromachined Microelectromechanical Systems (MEMS) accelerometers (RunScribe®, San Francisco, CA, USA) were used for this experiment. The two RunScribe pods were mounted on top of the foot in the shoelaces. All five athletes performed three maximum intensity runs: the 1st run was performed after a brief warmup with no prior exercise, then the 2nd and the 3rd run were performed in a fatigued state. Prior to the 2nd and the 3rd run, the athletes were asked to perform at maximum intensity for two minutes on an Assault AirBike to tire them. For all five athletes, there was a direct correlation between fatigue and an increase in the aggressiveness of the SRS. We noticed that for all five athletes for the 3rd run the average SRS peaks were significantly higher than for the 1st run and 2nd run (p < 0.01) at the same natural frequency of the athlete. This confirms our hypothesis that fatigue causes a decrease in the shock attenuation capacity of the musculoskeletal system thus potentially involving a higher risk of overuse injury.

Due to the recent development of the micro-launcher technology, soon nanosatellites are expected to be launched mainly as primary payloads and thus experience intense pyroshock events. This study proposes a novel CubeSat deployment system which alleviates such mechanical shock levels. The passive isolator Sorbothane thin films were integrated within the dynamic envelope of a testpod to evaluate the desired attenuation effects. A metal-to-metal mid-field shock testing (MFST) facility was manufactured to perform in-plane (IP) and out-of-plane (OOP) impacts. The MFST is capable of generating mechanical shock waves up to 10,000g for OOP direction and 5000g for IP excitations. The experiments illustrated that the Sorbothane isolators can attenuate shock levels by 3 dB and the flat adapter (mechanical joint) can attenuate shock levels by 4 dB. The measurements were successfully validated using the positive and the negative shock response spectrum (SRS) approach. In addition to that, the commercially available finite element analysis software ABAQUS was utilized to verify the experimental measurements and simulate the mechanical shock effects using explicit analysis. [ABSTRACT FROM AUTHOR]

Nut fasteners are produced by machines working around the clock. Companies generally operate with a run-to-failure or planned maintenance approach. Even with a planned maintenance schedule, however, undetected damage to the dies and non-die parts occurring between maintenance periods can cause considerable downtime and pervasive damage to the machine. To address this shortcoming, force data from the fourth and sixth dies of a six-die nut manufacturing machine were analysed using correlation to the best health condition on the force profile and on the force shock response spectrum profile. Fault features such as quality adjustments and damage to both die and non-die parts were detectable prior to required maintenance or machine failure. This detection was facilitated by the determination of health thresholds, whereby the force SRS profile generated a longer warning period prior to failure. The analytical approach could benefit the industry by identifying damage that would normally go undetected by operators, thereby reducing downtime, extending die life, enabling “as needed” maintenance, and optimising machine operation.

The initiating explosive shock environment of an aerospace mission has the characteristics of instantaneity, high amplitude and a wide frequency domain. An improved method based on the acceleration frequency response function (FRF) and virtual mode synthesis method (VMSS) is proposed to predict the pyroshock response of a spacecraft structure in a wide frequency domain. Firstly, the statistical energy analysis (SEA) model of the spacecraft structure was established, and the FRF and modal density of the model were obtained. Then, the paper explains how, due to the small number of modes in the low-frequency band, the calculation results of the SEA method in the low-frequency band were not accurate enough. The FRF of the SEA model in the low-frequency band was modified by an FRF test of the structure. Finally, the shock response spectrum (SRS) was obtained based on the VMSS and the modified FRF. A shock experiment on the spacecraft structure was conducted by using the shock experiment system, which is based on a light-gas gun. The accurate shock force function and acceleration response results were obtained. The numerical results based on the improved method are in line with those in the experiment. This verifies that the novel method can better grasp the response characteristics of the structure in the broadband domain. The novel method effectively improves the response prediction accuracy of the SEA model in the relatively low-frequency band. While ensuring the computational efficiency, more accurate shock response results in a wide frequency domain were obtained. The novel method presented in this paper provides support of numerical analysis for pyroshock response prediction of spacecraft structure in a wide frequency domain.

Satellites are exposed to various shock environments during launch. Large shock responses can be generated on rocket separation or deployment of solar arrays and antennas when the strain energy of retained parts is released. Therefore, a test to verify the shock resistance of spacecraft components is necessary. Specially designed separation mechanisms or explosive devices are used to facilitate separation but such methods are expensive to test. To reduce this cost, alternative methods (such as the falling weight shock method) are used but the shock excitation source and structural propagation paths of the test apparatus are different from the operational configurations. This poses problems in making adjustments to match the specified Shock Response Spectrum (SRS) and often causes over- and under-testing, decreasing confidence in the test. This paper reports the results of our study to improve the accuracy of the SRSs of satellite components in shock testing. In the mechanical impact method implemented by the drop weight shock test, the SRS is usually adjusted by changing the material at the impact point, but this method is often inadequate. Rather than changing the hardness of the impact point we modified the SRS adjustment by altering the structure in the path of shock propagation. [ABSTRACT FROM AUTHOR]

An improved method based on the Hybrid Finite Element-Statistical Energy Analysis (FE-SEA) method and quasi-steady state theory is proposed to predict the response of spacecraft structure during the process of pyrotechnics separation. Firstly, the amplitude–frequency value of shock load is obtained by using time-frequency conversion technology. Then, according to the frequency response characteristics of each part of the spacecraft structure, a more accurate hybrid FE-SEA model is established. The piecewise loading method is used to predict the response of the hybrid model. Finally, the time domain response results are reconstructed, and the shock response spectrum (SRS) is calculated. Based on the test system of simulating pyroshock, the shock experiment of spacecraft structure is conducted. The high frequency and high velocity character of pyroshock could be effectively simulated, and an accurate shock force function could be obtained through the experiment. This indicates that the numerical results are in line with the ones of the experiment. The SRS obtained from experiments and calculations have similar trends and amplitudes. This conclusion verifies the rationality and sufficient accuracy of the novel method in this paper. The novel method presented in this paper greatly improves the computational efficiency. At the same time, it provides theoretical guidance for shock response prediction of spacecraft structure by steady-state methods.

Purpose. The article is aimed to analyze the increase in the effectiveness of traditional methods for carrying out shock tests of land vehicles, in order to assess their strength, reliability and durability. Methodology. To achieve this purpose, the authors of the article developed a technique for conducting impact tests and effective algorithm based on the ideas and methodological proposals contained in the UN Guidelines on the “Recommendations for Transportations of Dangerous Goods”. Findings. With the use of the modern programming language SI-Sharp, a specialized software package was created that implements the algorithm for handling shock processes, which has a "friendly" interface with the user of this complex and other software products of the computing environment powered by Windows. With the application of this complex, the results of tests of the tank-container of the model CTL-26/0.4, type UN T14 under different shock loading (collision rates), geometric, inertial and damping parameters of this design were processed. As a result, an objective evaluation of the properties of the tested object was obtained, and a conclusion was made that the calculated shock response spectrum (SRS) was exceeded, its minimum permissible value in the entire spectrum of the investigated frequencies. Originality. For the first time, a complex theoretical and practical approach to the study of the strength, reliability, and durability of transport mechanical structures subjected to impact loads on the basis of the evaluation of the impact response spectra was realized. Practical value. The application of the proposed methodology and the developed software package for carrying out shock tests made it possible to increase the reliability of these tests, to shorten the time of their testing and to process the results. The results of the testing of the tank-container tests showed that this vehicle fully provides the required normative parameters of strength, reliability and durability. This is also confirmed by the fact that after the shock tests carried out in the structure under investigation there were no structural damages, residual deformations and no leakage of the goods transported. The article concludes that it is possible to use the developed technique for carrying out shock tests and implementing a software package for carrying out similar tests of any land vehicles.