Jacob Dodson

Real-Time State Detection in Highly Dynamic Systems

This article investigates the feasibility of real-time state detection on a microsecond timescale for use in highly dynamic systems and presents an experimental setup of a high-rate dynamic system coupled with real-time measurement architecture with the goal of detecting changes in the interfacial state of the system. The feasibility of microsecond state detection is assessed through a preliminary timing study. The experimental setup consists of two colliding aluminum bars and includes the option of changing the bar’s boundary conditions and the interface material between the bars. A piezoelectric transducer will be used for detecting changes in dynamic interfacial state by employing electromechanical impedance monitoring and the measurement data from this will be acquired and processed at high speeds using deterministic real-time tools and methodology. Damage detection algorithms from the structural health monitoring community will be used for rapid detection of changes in state. The eventual goal of this work is to adapt currently used methods or to develop entirely new high speed state detection algorithms to be implemented on the real-time system for state detection. This technology has the potential to be used in many applications, including the aerospace, civil, and energy industries among others.

Constitutive Response of Electronics Materials

Electronics in mission- or safety-critical systems are expected to survive a wide range of harsh environments including thermal cycling, thermal ageing, vibration, shock, and combinations of the aforementioned stresses. The materials used in these electronic systems are diverse and frequently change as the electronics industry rapidly innovates. These materials are dual use, fulfilling both electrical and mechanical functions. Of particular interest are electronic materials classes such as polymers (e.g., encapsulants/potting and packaging), composites (e.g., hard potting and printed circuit boards), and interconnect materials (e.g., solder). Thus, predicting the operational response of electronics systems in harsh environments requires understanding of the materials constitutive response to the environmental characteristics for all the relevant materials. The paper estimates the rate-, temperature-, and pressure-dependent constitutive response of representative electronic materials. Experimental response of circuit boards, potting materials, and solder interconnects are measured in low and intermediate strain rate dynamic tests. Traditional mechanical sensors (e.g. strain gages and accelerometers) are complemented by non-contact techniques (e.g., laser velocimetery, high speed digital image correlation) to obtain high fidelity experimental data on material response. Estimates of the corresponding constitutive parameters are calculated, and observed features of the dynamic response are discussed.

Dynamics of Interfaces with Static Initial Loading

Accurately modeling the dynamic response of structural interfaces under high rate loading conditions is challenging due to lack of focused studies and validation data. In order to support the development and validation of accurate physics-based models of these interface dynamics, simulations and experiments using combined static torsional loads with dynamic compressive loading are performed. A ballistic impact generates dynamic compressive stress waves that propagate across the threaded interface of two coupled metallic bars with a known static torque. Strong phenomenological evidence of the release and conversion of static torsional energy due to the applied dynamic loads is seen in time-frequency analysis. The frequency band structure of the dynamic waves are also observed to vary under certain conditions. Applied torque is shown to relax almost completely during an experiment, with significant rotation of the transmission bar relative to the incident bar. The mechanism is believed to be release of the static torque and the generation of torsional waves.

Investigating the thermally induced acoustoelastic effect in isotropic media with Lamb waves.

Elastic wave velocities in metallic structures are affected by variations in environmental conditions such as changing temperature. This paper extends the theory of acoustoelasticity by allowing thermally induced strains in unconstrained isotropic media, and it experimentally examines the velocity variation of Lamb waves in aluminum plates (AL-6061) due to isothermal temperature deviations. This paper presents both thermally induced acoustoelastic constants and thermally varying effective Youngs modulus and Poissons ratio which include the third order elastic material constants. The experimental thermal sensitivity of the phase velocity (∂v(P)/∂θ) for both the symmetric and antisymmetric modes are bounded by two theories, the acoustoelastic Lamb wave theory with thermo-acoustoelastic tensors and the thermoelastic Lamb wave theory using an effective thermo-acoustoelastic moduli. This paper shows the theoretical thermally induced acoustoelastic Lamb wave thermal sensitivity (∂v(P)/∂θ) is an upper bound approximation of the experimental thermal changes, but the acoustoelastic Lamb wave theory is not valid for predicting the antisymmetric (A0) phase velocity at low frequency-thickness values, <1.55 MHz mm for various temperatures.

Introduction to State Estimation of High-Rate System Dynamics

Engineering systems experiencing high-rate dynamic events, including airbags, debris detection, and active blast protection systems, could benefit from real-time observability for enhanced performance. However, the task of high-rate state estimation is challenging, in particular for real-time applications where the rate of the observer’s convergence needs to be in the microsecond range. This paper identifies the challenges of state estimation of high-rate systems and discusses the fundamental characteristics of high-rate systems. A survey of applications and methods for estimators that have the potential to produce accurate estimations for a complex system experiencing highly dynamic events is presented. It is argued that adaptive observers are important to this research. In particular, adaptive data-driven observers are advantageous due to their adaptability and lack of dependence on the system model.

Variable Input Space Observer for Structural Health Monitoring of High-Rate Systems

The development of high-rate structural health monitoring methods is intended to provide damage detection on timescales of 10 µs -10ms where speed of detection is critical to maintain structural integrity. Here, a novel Variable Input Observer (VIO) coupled with an adaptive observer is proposed as a potential solution for complex high-rate problems. The VIO is designed to adapt its input space based on real-time identification of the system’s essential dynamics. By selecting appropriate time-delayed coordinates defined by both a time delay and an embedding dimension, the proper input space is chosen which allows more accurate estimations of the current state and a reduction of the convergence rate. The optimal time-delay is estimated based on mutual information, and the embedding dimension is based on false nearest neighbors. A simulation of the VIO is conducted on a two degree-of-freedom system with simulated damage. Results are compared with an adaptive Luenberger observer, a fixed time-delay observer, and a Kalman Filter. Under its preliminary design, the VIO converges significantly faster than the Luenberger and fixed observer. It performed similarly to the Kalman Filter in terms of convergence, but with greater accuracy.The development of high-rate structural health monitoring methods is intended to provide damage detection on timescales of 10 µs -10ms where speed of detection is critical to maintain structural integrity. Here, a novel Variable Input Observer (VIO) coupled with an adaptive observer is proposed as a potential solution for complex high-rate problems. The VIO is designed to adapt its input space based on real-time identification of the system’s essential dynamics. By selecting appropriate time-delayed coordinates defined by both a time delay and an embedding dimension, the proper input space is chosen which allows more accurate estimations of the current state and a reduction of the convergence rate. The optimal time-delay is estimated based on mutual information, and the embedding dimension is based on false nearest neighbors. A simulation of the VIO is conducted on a two degree-of-freedom system with simulated damage. Results are compared with an adaptive Luenberger observer, a fixed time-delay observer, ...

Nonlinear High Fidelity Modeling of Impact Load Response in a Rod

In this paper, wave propagation through a polyurethane rod is studied by using an experimental system and through performing high fidelity numerical simulations. The rod model for the polyurethane rod is prepared accounting for the possibility of a material nonlinearity. Due to a significant impedance mismatch between the titanium transmission bar and the polyurethane rod along with the high damping level of the polyurethane, only a small amplitude, linear response was observed and predicted in the polyurethane rod. Ongoing work will focus on impedance matching in order to transfer greater amounts of energy into the polyurethane rod so that the nonlinear stress-strain relationship can be studied for larger magnitude response conditions.

Comparative Analysis of Triaxial Shock Accelerometer Output

Shock accelerometer internal and mounting dynamics are analyized and the contribution to the sensor output is evaluated. This includes an analysis of uniaxial and triaxial accelerometer cross-talk (cross axis sensitivity effects), the filtering characteristics of polysulfide films, and the influence of triaxial block transient dynamic response on the shock accelerometer output. It is shown that the polysulfide acts as a lowpass filter and dissipates energy in the frequency range of sensor resonance. Features in the data, such as energy spectral density, cross axis sensitivity, and mode shapes of the triaxial block are highlighted.

High-g Shock Acceleration Measurement Using Martlet Wireless Sensing System

This paper reports the latest development of a wireless sensing system, named Martlet, on high-g shock acceleration measurement. The Martlet sensing node design is based on a Texas Instruments Piccolo microcontroller, with clock frequency programmable up to 90 MHz. The high clock frequency of the microcontroller enables Martlet to support high-frequency data acquisition and high-speed onboard computation. In addition, the extensible design of the Martlet node conveniently allows incorporation of multiple sensor boards. In this study, a high-g accelerometer interface board is developed to allow Martlet to work with the selected microelectromechanical system (MEMS) high-g accelerometers. Besides low-pass and high-pass filters, amplification gains are also implemented on the high-g accelerometer interface board. Laboratory impact experiments are conducted to validate the performance of the Martlet wireless sensing system with the high-g accelerometer board. The results of this study show that the performance of the wireless sensing system is comparable to the cabled system.

Adaptive Observers for Structural Health Monitoring of High-Rate, Time-Varying Dynamic Systems

Safe and reliable operation of hypersonic aircraft, space structures, advanced weapon systems, and other high-rate dynamic systems depends on advances in state estimators and damage detection algorithms. High-rate dynamic systems have rapidly changing input forces, rate-dependent and time-varying structural parameters, and uncertainties in material and structural properties. While current structural health monitoring (SHM) techniques can assess damage on the order of seconds to minutes, complex high-rate structures require SHM methods that detect, locate, and quantify damage or changes in the structure’s configuration on the microsecond timescale.