In this study, we numerically implemented the first iteration of a novel phase field based theoretical framework to predict the fracture mechanics of Ni2MnGa MSMAs. The proposed variational phase field fracture mechanics model uses an energy balance framework that accounts for the strain energy (elastic and reorientation), Zeeman and magnetic anisotropy energies, as well as the fracture surface energy. The model predictions are preliminarily validated against experimental data obtained during Vickers micro indentation, while a formal experimental program is developed for traditional tests on crack initiation and growth.

The Polymer Mechanics Research Laboratory at Auburn University contributes fundamental knowledge to the field of time dependent, thermomechanical behavior of polymers, which contributes to core functions of autonomy in engineered matter, such as sensory mechanisms, actuation capabilities, and adaptive mechanical-material frames. In this talk, we will provide an overview of ongoing research relevant to the multifunctional materials and adaptive structures community, with an emphasis on the deformation and actuation capabilities of polymeric materials and structures. Topics include: (1) mechanics of self-folding polymer origami: we utilize pre-strained polymer sheets that change shape in response to external stimuli. Compactly stored sheets can be transformed into three-dimensional structures on demand. These materials are proposed for use as actuators in deployable space structures. (2) Reconfigurable mechanical metamaterals: tessellated unit cells dictate the macroscopic behavior of the structure. Structures can be reconfigured through thermal and mechanical processes to tailor properties to specific applications. Of particular interest are bistable structures and auxetic metamaterials. (3) Electrospun smart sensors: the use of conducting polymers in the electrospinning processes provides additional functionality to non-woven mats. These sensors are envisioned for use at the human-machine interface. The processing conditions used to fabricate the non-woven mats influence sensor performance and human factors such as breathability. These research activities are broadly conducted by graduate and undergraduate researchers working in a collaborative environment.

In this work, we seek to fabricate self-folding liquid crystal elastomer (LCE) composite films. Liquid crystal elastomers (LCEs) are a class of smart, multifunctional materials that can be imparted with enhanced, anisotropic mechanical properties through the alignment of crystalline domains. Crystalline order decreases with increasing temperature, and long-range order is lost above the nematic to isotropic transition temperature, TNI. This enables programmable, reversible actuation in response to temperature changes. The envisioned composite films comprise domains of active, monodomain LCEs to drive reversible self-folding, which are adhered to passive, thin films that serve as a framework to guide the self-folding response. LCEs will be synthesized using a two-stage thiol-acrylate Michael addition and photopolymerization (TAMAP) reaction. The first-stage consists of a room temperature cure to form polydomain films, and a second-stage photopolymerization of the mechanically deformed LCE film forms aligned liquid crystal monodomains. Composite films will be molded to a folded state prior to the second stage cure such that heating above TNI produces a reversible unfolding response. We characterize the self-folding behavior of these materials using a series of single-fold and multiple, intersecting fold geometries. We envision application of these composite films as actuators in soft robotics and morphing surfaces.

There is currently a great demand for biomimetic advanced materials with simple and programmable production procedures, and polymeric actuators with soft-robotic capabilities are in the spotlight of this section. In this study, we will illustrate 4D printing phenomena by building actuator devices using various polymeric systems. Shape memory based hydrogels and composite polymers have been developed, and their 3D fabrication and physical properties have been extensively studied to understand how their responses vary with swelling degree, temperature, and light.

Space represents a harsh environment for all materials. This is particularly challenging for shape memory polymers (SMPs), which show significant potential for lightweight actuators for deployable space structures. Relevant conditions include UV radiation, temperature variations, and vacuum. Polymers, when exposed to such environment for prolonged period (aging), begin to break down structurally and thermodynamic properties, such as enthalpy, entropy, and specific volume, change over time. This leads to permanent modification of mechanical properties such as decreased strength and increased brittleness of the polymer. The shape recovery performance of shape memory polymer is dependent on its thermodynamic properties and energy associated with UV aging can be evaluated through a differential scanning calorimetry (DSC) test. Previous studies focus on the effects of UV exposure on chemical degradation of polymers. However, limited research has been conducted towards studying shape recovery performance of UV aged polymer through thermomechanical prestrain followed by shape recovery process. In this study, we expose SMPs in a UV environment followed by shape recovery experiments where they are prestrained and recovered at various thermomechanical conditions such as recovery temperature, strain rate and aging time. Furthermore, we use characterization techniques such as FTIR and SEM to evaluate the amount of physical degradation of SMP as a result of UV aging process. The results obtained from this study will provide insight into recovery capabilities of a SMP for space exploration.

This study focuses on the synthesis of network polymers using free radical initiated thiol-ene reaction to create flexible and soft polymeric materials. Ionic liquid-based network polymers termed as "ionic gels," "ionic porous polymers," and PDMS-based elastomers and nanocomposites have been synthesized, and their physico-chemical properties along with 3D printability have been extensively studied. The structure-property relationship study of the synthesized network polymers demonstrated tunable mechanical and morphological aspects, while the sensing study revealed piezo-capacitive sensing characteristics.. These novel designable materials can find prospective scope in the fields of MEMS, microfluidics, and sensors.

The performance of bistable composite laminates is affected significantly by environmental conditions like moisture, resulting in changes in their structural performance. This study characterizes the moisture effect on the maximum height, curvature, and snap-through load of the [0/90] CFRP laminates in a 100% RH environment. Laminates are submerged in a de-ionized water bath up to moisture saturation, and their maximum height, curvature, and snap-through load are measured. This work updates an existing analytical and FEA model to incorporate the effect of moisture on these parameters by expressing the combined thermal and moisture expansion coefficients as a function of diffusivity, time, and thickness. Test results revealed a significant reduction in all three parameters during the initial rapid moisture uptake period of Fickian absorption, followed by a gradual reduction at a substantially lower rate. The FEA and analytical model demonstrated good agreement with the test results.