Travis L. Turner

A New Thermoelastic Model for Analysis of Shape Memory Alloy Hybrid Composites

A constitutive model and a finite element formulation are developed for predicting the thermomechanical response of SMA hybrid composite structures subjected to combined thermal and mechanical loads. The constitutive model is valid for constrained, restrained, or free recovery behavior with appropriate measurements of basic SMA material properties. The model captures the material nonlinearity of the SMA with temperature and more accurately captures the mechanics of composites with embedded SMA actuators as compared to other recently developed approaches. The constitutive and finite element models are amenable to commercial code implementation. The fundamental thermoelastic behavior of such structures is described in physical terms and related to the governing equations. It is shown that alloy selection is imperative for achieving the desired performance with respect to the application environment. It is also shown that fundamental efforts to strategically place actuators can produce dramatic performance improvements. Numerical results are shown for glass-epoxy beam specimens with embedded Nitinol actuators. Control of critical buckling temperature, thermal post-buckling deflection, and random response are demonstrated.

Modeling, Fabrication, and Testing of a SMA Hybrid Composite Jet Engine Chevron Concept

This study presents a fabrication method, bench top test results, and numerical model validation for a novel adaptive jet engine chevron concept based upon embedding shape memory alloy (SMA) actuators in a composite laminate, termed a SMA hybrid composite (SMAHC). The approach for fabricating the adaptive SMAHC chevrons involves embedding prestrained Nitinol actuators on one side of the mid-plane of the composite laminate such that thermal excitation generates a thermal moment and deflects the structure. A rigorous and versatile test system for control and measurement of the chevron deflection performance is described. A recently commercialized constitutive model for SMA and SMAHC materials is used in the finite element code ABAQUS to perform nonlinear static analysis of the chevron specimens. Excellent agreement is achieved between the predicted and measured chevron deflection performance, thereby validating the numerical model and enabling detailed design of chevron prototype(s) and similar structures.

Fabrication and Characterization of SMA Hybrid Composites

Results from an effort to fabrication shape memory alloy hybrid composite (SMAHC) test specimens and characterize the material system are presented in this study. The SMAHC specimens are conventional composite structures with an embedded SMA constituent. The fabrication and characterization work was undertaken to better understand the mechanics of the material system, address fabrication issues cited in the literature, and provide specimens for experimental validation of a recently developed thermomechanical model for SMAHC structures. Processes and hardware developed for fabrication of the SMAHC specimens are described. Fabrication of a SMAHC laminate with quasi-isotropic lamination and ribbon-type Nitinol actuators embedded in the 0°layers is presented. Beam specimens are machined from the laminate and are the focus of recent work, but the processes and hardware are readily extensible to more practical structures. Results of thermomechanical property testing on the composite matrix and Nitinol ribbon are presented. Test results from the Nitinol include stress-strain behavior, modulus versus temperature, and constrained recovery stress versus temperature and thermal cycle. Complex thermomechanical behaviors of the Nitinol and composite matrix are demonstrated, which have significant implications for modeling of SMAHC structures.

Piezoelectric Shunt Vibration Damping of F-15 Panel under High Acoustic Excitation

At last years SPIE symposium, we reported results of an experiment on structural vibration damping of an F-15 underbelly panel using piezoelectric shunting with five bonded PZT transducers. The panel vibration was induced with an acoustic speaker at an overall sound pressure level (OASPL) of about 90 dB. Amplitude reductions of 13.45 and 10.72 dB were achieved for the first and second modes, respectively, using single- and multiple-mode shunting. It is the purpose of this investigation to extend the passive piezoelectric shunt- damping technique to control structural vibration induced at higher acoustic excitation levels, and to examine the controllability and survivability of the bonded PZT transducers at these high levels. The shunting experiments was performed with the Thermal Acoustic Fatigue Apparatus (TAFA) at the NASA Langley Research Center using the same F-15 underbelly panel. The TAFA is a progressive wave tube facility. The panel was mounted in one wall of the TAFA test section using a specially designed mounting fixture such that the panel was subjected to grazing-incidence acoustic excitation. Five PZT transducers were used with two shunt circuits designed to control the first and second modes of the structure between 200 and 400 Hz. We first determined the values of the shunt inductance and resistance at an OASPL of 130 dB. These values were maintained while we gradually increased the OASPL from 130 to 154 dB in 6-dB steps. During each increment, the frequency response function between accelerometers on the panel and the acoustic excitation measured by microphones, before and after shunting, were recorded. Good response reduction was observed up to the 148dB level. The experiment was stopped at 154 dB due to wire breakage from vibration at a transducer wire joint. The PZT transducers, however, were still bonded well on the panel and survived at this high dB level. We also observed shifting of the frequency peaks toward lower frequency when the OASPL was increased. Detailed experimental results will be presented.

Dynamic response tuning of composite beams by embedded shape memory alloy actuators

The thermomechanical performance of a shape memory alloy hybrid composite beam specimen is demonstrated and used in a preliminary validation study of a recently developed constitutive model and finite element formulation for analysis of such structures. A brief description of the thermoelastic formulation is given. A material system consisting of a glass/epoxy matrix with embedded Nitinol actuators was chosen for this study. Results from Nitinol material characterization testing, beam specimen fabrication processes, and base acceleration testing for measuring the dynamic response performance in presented. Selected results from the dynamic test are shown, interpreted, and compared with predictions form the FE model. Elimination of a thermal post-buckling deflection by the activated SMA was observed. The fundamental natural frequency is shown to increase by a facto of 5.3 and the RMS displacement response is attenuated by a factor 6.4. Preliminary comparisons between predicted and measured performance is good. Discrepancies are attributable to insufficient knowledge of the matrix material properties at elevated temperature.

Analysis of SMA Hybrid Composite Structures in MSC.Nastran and ABAQUS

A thermoelastic constitutive model for shape memory alloy (SMA) actuators embedded in a composite structure, termed an SMA hybrid composite (SMAHC), was recently implemented in the commercial finite element codes MSC.Nastran and ABAQUS. The model can be easily implemented in any code that has the capability for analysis of laminated composite structures with temperature-dependent material properties. The model is also relatively easy to use, and requires input of only fundamental engineering properties. A brief description of the model is presented, followed by a discussion of implementation and usage in commercial codes. Results are presented from static and dynamic analysis of SMAHC beams of two types: a beam clamped at each end and a cantilever beam. Nonlinear static (post-buckling) and random response analyses are demonstrated for the first specimen. Static deflection (shape) control is demonstrated for the cantilever beam. Approaches for modeling SMAHC material systems with embedded SMA in ribbon and small round wire product forms are demonstrated and compared. The results from commercial codes are compared with those from a research code as validation of commercial implementations; excellent correlation is achieved in all the cases.

Experimental validation of a thermoelastic model for SMA hybrid composites

This study presents results from experimental validation of a recently developed model for predicting the thermomechanical behavior of shape memory alloy hybrid composite (SMAHC) structures, composite structures with an embedded SMA constituent. The model captures the material nonlinearity of the material system with temperature and is capable of modeling constrained, restrained, or free recovery behavior from experimental measurement of fundamental engineering properties. A brief description of the model and analysis procedures is given, followed by an overview of a parallel effort to fabricate and characterize the material system of SMAHC specimens. Static and dynamic experimental configurations for the SMAHC specimens are described and experimental results for thermal post-buckling and random response are presented. Excellent agreement is achieved between the measured and predicted results, fully validating the theoretical model for constrained recovery behavior of SMAHC structures.

Finite Element Analysis of Adaptive-Stiffening and Shape-Control SMA Hybrid Composites

Shape memory alloy (SMA) hybrid composites with adaptive-stiffening or morphing functions are simulated using finite element analysis. The composite structure is a laminated fiber-polymer composite beam with embedded SMA ribbons at various positions with respect to the neutral axis of the beam. Adaptive stiffening or morphing is activated via selective resistance heating of the SMA ribbons or uniform thermal loads on the beam. The thermomechanical behavior of these composites was simulated in ABAQUS using user-defined SMA elements. The examples demonstrate the usefulness of the methods for the design and simulation of SMA hybrid composites.

Design, Fabrication, and Testing of SMA Enabled Adaptive Chevrons for Jet Noise Reduction

This study presents the status and results from an effort to design, fabricate, and test an adaptive jet engine chevron concept based upon embedding shape memory alloy (SMA) actuators in a composite laminate, termed a SMA hybrid composite (SMAHC). The approach for fabricating the adaptive SMAHC chevrons involves embedding prestrained Nitinol actuators on one side of the mid-plane of the composite laminate such that thermal excitation generates a thermal moment and deflects the structure. A glass-epoxy pre-preg/Nitinol ribbon material system and a vacuum hot press consolidation approach are employed. A versatile test system for control and measurement of the chevron deflection performance is described. Projection moire interferometry (PMI) is used for global deformation measurement and infrared (IR) thermography is used for 2-D temperature measurement and feedback control. A recently commercialized constitutive model for SMA and SMAHC materials is used in the finite element code ABAQUS to perform nonlinear static analysis of the chevron prototypes. Excellent agreement is achieved between the predicted and measured chevron deflection performance, thereby validating the design tool. Although the performance results presented in this paper fall short of the requirement, the concept is proven and an approach for achieving the performance objectives is evident.

Analysis of SMA hybrid composite structures using commercial codes

A thermomechanical model for shape memory alloy (SMA) actuators and SMA hybrid composite (SMAHC) structures has been recently implemented in the commercial finite element codes MSC.Nastran and ABAQUS. The model may be easily implemented in any code that has the capability for analysis of laminated composite structures with temperature dependent material properties. The model is also relatively easy to use and requires input of only fundamental engineering properties. A brief description of the model is presented, followed by discussion of implementation and usage in the commercial codes. Results are presented from static and dynamic analysis of SMAHC beams of two types; a beam clamped at each end and a cantilevered beam. Nonlinear static (post-buckling) and random response analyses are demonstrated for the first specimen. Static deflection (shape) control is demonstrated for the cantilevered beam. Approaches for modeling SMAHC material systems with embedded SMA in ribbon and small round wire product forms are demonstrated and compared. The results from the commercial codes are compared to those from a research code as validation of the commercial implementations; excellent correlation is achieved in all cases.