Seminars

Emile Naous
Ph.D. Candidate
Aerospace Engineering and Engineering Mechanics
The University of Texas at Austin

January 29, 2026 | 15:30-17:30 am

Mechanically lined pipe, composed of a carbon steel carrier and a thin-walled corrosion-resistant alloy (CRA) liner, is a cost-effective product for protecting against corrosive contents. The two components are held together by a mechanical bond induced by manufacture. Under bending to plastic strain levels such as those imposed by the reel-lay pipeline installation method, the liner separates from the carrier and develops localized wrinkles that evolve into large amplitude buckles. Reeling induces repeated bending, straightening, and reverse bending, so lined pipe must be qualified for multiple bending cycles. Accordingly, this work focuses on the response of lined pipe and the evolution of liner instability under cyclic bending and cyclic reeling using custom large-scale finite element models.

The cyclic elastic-plastic behavior of X65 carbon steel and Alloy 825 and the Bauschinger rounding of the stress-strain response under reverse loading are modeled using a combined isotropic-kinematic hardening model. It was found that similar liner instabilities observed under monotonic bending are activated during cycling; however, in this case, liner separation, wrinkling and buckling accumulate progressively with each cycle. The liner separation corresponding to criticality under monotonic bending was found to mark the onset of accelerated wrinkle growth under all cyclic loading histories considered. The constraining effect of girth welds on liner stability under cyclic bending is also investigated.

Cyclic reeling is found to be less severe than cyclic pure bending to the same curvature level, but repeated winding and unwinding ultimately lead to the same instabilities. Internal pressure is shown to significantly delay liner instability, while geometric imperfections and girth welds act as local weak zones where wrinkling initiates. The findings are synthesized into design guidelines for the safe cyclic bending and reeling of lined pipes.

Contact: Stelios Kyriakides (skk@mail.utexas.edu)

Zhengjie Li
Ph.D. Candidate
Aerospace Engineering and Engineering Mechanics
The University of Texas at Austin

Feb 24, 2026 Tuesday 15:30-17:30 am

Tactile electronic skin (e-skin) that replicates both the mechanical compliance and sensory functions of natural skin is essential for next-generation physical hu-man–robot interaction (pHRI). Capacitive pressure sensors (CPS) are a core sensing modality in e-skin systems due to their low power consumption, compatibility with soft materials, and ability to detect static and dynamic pressures. Despite extensive development, most CPS designs suffer from a fundamental sensitivity–pressure trade-off, where sensitivity decreases with increasing pressure. In addition, CPS responses are often coupled with in-plane deformation modes such as stretch and shear, complicating signal interpretation in soft and wearable applications. To overcome these limitations, hybrid response pressure sensors (HRPS) and stretch-insensitive hybrid response pressure sensors (SHRPS) were previously developed by integrating electrically conductive porous nanocomposites (PNCs) with ultrathin dielectric layers. These sensors exhibit coupled piezoresistive and piezo capacitive responses, enabling enhanced sensitivity over a wide pressure range and effective decoupling of pressure from stretch and shear. However, the electromechanical mechanisms underlying these advantages remained unclear, and a unified framework to guide sensor design and operation has been lacking. This dissertation develops a unified electromechanical framework to explain and predict CPS sensitivity across material systems, sensor architectures, and loading conditions. The sensitivity–pressure trade-off is shown to be governed by key parameters across three interconnected stages: (i) fabrication-stage material and structural parameters, including Young’s modulus, dielectric loss, and dielectric layer thickness;(ii) post-fabrication tuning via excitation frequency; and (iii) deformation mechanisms that decouple out-of-plane compression from in-plane stretch and shear. First, the frequency-dependent behavior of HRPS is systematically studied, demonstrating that excitation frequency acts as an effective post-fabrication tuning parameter through two governing dimensionless quantities. Second, the deformation mechanisms responsible for the stretch-insensitive behavior of SHRPS are elucidated, showing that the electrical response is dominated by pressure-induced out-of-plane deformation. Third, a generalized double-branch equivalent circuit model is developed to unify CPS with engineered dielectrics, HRPS, and CPS with engineered electrodes, yielding a closed-form sensitivity expression that links electromechanical response to material properties, structural parameters, and interfacial conditions.

Zoom Link – https://utexas.zoom.us/j/85309616561

Contact: Nanshu Lu (nanshulu@utexas.edu)

Jinlong Guo
Ph.D. Candidate
Aerospace Engineering and Engineering Mechanics
The University of Texas at Austin

June 16, 2026 Tuesday 10:00-11:00 am

We present the results of an investigation of crack nucleation and propagation in polydimethylsiloxane (PDMS) elastomers using the classical poker-chip experiment. The first objective of this investigation is to quantitatively characterize the evolution of crack nucleation and growth, not only through the usual macroscopic load–displacement response, but also through synchronized optical images with high spatial resolution and adequate temporal resolution, augmented with X-ray computed tomography scans. The experiments reveal that the first interior crack does not nucleate at the radial center, where the hydrostatic stress is largest, but instead nucleates at some distance away from the center. When the diameter-to-thickness aspect ratio is sufficiently large, failure is dominated by the nucleation of multiple microcracks. In contrast, specimens with smaller aspect ratios tend to nucleate fewer cracks, and failure is dominated by the growth of these cracks.

We then show that a local fracture criterion is not sufficient to explain the off-center crack nucleation. To address this limitation, we propose a new nucleation criterion that combines the hydrostatic stress with a nonlocal measure of the strain energy. The stability and slanted growth of macro cracks are then quantified through calculations of the energy release rate. We further show that subsequent crack nucleation can be explained by the proposed nucleation criterion together with the stable growth of pre-existing cracks. This reveals why specimens with larger diameter-to-thickness ratios tend to nucleate more independent cracks, while the inter-crack distance appears to be independent of the aspect ratio. Finally, the poker-chip experiment is extended to PDMS elastomers with different composition ratios, revealing a transition in the crack nucleation and growth behavior.

Zoom Link:  https://utexas.zoom.us/j/2079375792pwd=jibj2pmpr0eIBsQFp9dn81WiSQfFxH.1&omn=87802599346 – Password: fracture

Contact:  K. Ravi-Chandar (ravi@utexas.edu)

Dr. Xin (Cindy) Yee
Assistant Professor
Department of Mechanical and Aerospace Engineering
University of Colorado Colorado Springs

January 13, 2026

Encapsulated microbubbles (EMBs) are used in biomedicine for both diagnostic and therapeutic purposes that include ultrasound imaging and targeted drug delivery. A data-driven method to control the oscillations of EMBs using the applied acoustic field is presented based on Koopman operator theory, which is a method for transforming a nonlinear dynamical system on a state space into a linear system on an infinite-dimensional function space. This method preserves the underlying nonlinear dynamics of the system, and the function spaces can be approximated through data-driven methodologies, which enables the application of classical linear control strategies to the nonlinear system. Here, we apply a Koopman linear quadratic regulator (KLQR) to control the nonlinear oscillations of a EMB through the applied acoustic field.  Results are presented that demonstrate the effectiveness of the modified KLQR controller in driving the EMB to follow arbitrarily-prescribed radial oscillations and stabilize at nonequilibrium radii.

Bio: Dr. Xin (Cindy) Yee is an Assistant Professor in the Department of Mechanical and Aerospace Engineering at the University of Colorado-Colorado Springs. She received her Bachelor of Science degree in Mechanical Engineering from MIT and both Master’s and Ph.D. degrees in Engineering from Caltech. Her expertise is in data science applications within engineering sciences.

Contact: Jin Yang (jin.yang@austin.utexas.edu)

Dr. Qing Tu
Assistant Professor
Materials Science and Engineering
Texas A&M University

January 20, 2026

2D metal halide perovskites (MHPs) are emerging family of low-cost, high-performance semiconductor materials for numerous energy and electronics applications. Mechanical stress is ubiquitously found in their applications and causes stability issues, which calls for a thorough understanding of the mechanical behaviors of 2D MHPs in both pristine form and under service environments. This talk will overview the research effort in my lab in the past 6 years on understanding the mechanical behavior of 2D MHPs. We will first establish a structure-property relationship regarding the in-plane elastic properties of 2D MHPs and compare the results to those from the out-of-plane directions. An interesting in-plane vs. out-of-plane mechanical anisotropy is uncovered, which can be tuned over a wide range by controlling the chemistry of the materials. We further employ the angle-resolved Brillouin Spectroscopy to directly measure the in-plane stiffness matrix and shed light on the in-plane elastic anisotropy of these materials. We will then show an anomalous thermo-mechanical behavior of 2D MHPs compared to other low-dimensional systems. Our results suggest that this thermo-mechanical anomaly is likely arising from the order-to-disorder transition of the organic spacer molecules inside the crystal structure. Finally, we report the creep and fatigue behavior of 2D MHPs under subcritical, time-dependent loading conditions. 2D MHPs exhibit better fatigue resilience compared to typical polymer materials, and can survive over one billion cycles when the mean stress is about 40% of their fracture strength. Failure morphology suggests the presence of an unexpected plastic deformation in these ionic crystals at low mean stress, which might be responsible for the long fatigue lifetime, but is significantly suppressed at high mean stress. Our results will provide invaluable insights to improve the mechanical reliability of 2D MHPs and pave the way for commercializing devices based on these materials.

Contact:  Rui Huang (ruihuang@mail.utexas.edu)

Dr. Yunlan Zhang
Assistant Professor
Fariborz Maseeh Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin

March 03, 2026

Conventional architected cellular materials have fixed configurations and absorb mechanical energy through irreversible plastic deformation, limiting them to single use and making compact stowage challenging. Here, we present architected instability-based metamaterials (AIMs) as a reusable, tunable, and deployable alternative. AIMs consist of numerous unit cells comprising multistable mechanisms that achieve large, reversible deformation while absorbing and dissipating energy. The behavior of AIMs can be tuned through four key design parameters: geometry, topology, material distribution, and hinge configuration. Tailoring unit cell geometry and topology controls energy absorption characteristics and deformation pathways. Strategically assigning multiple materials at different locations enables stimulus-responsive behavior, such as shape recovery triggered by heat. Incorporating kirigami-inspired rigid folding strategies through hinge design enables structures that fold into compact volumes for transportation and expand into functional metamaterials at the destination. Together, these capabilities—reusability, tunability, and deployability— make AIMs well-suited for aerospace applications where weight, volume, and reliability are critical constraints. This seminar presents a design approach integrating analytical and numerical models to achieve tunable multistability and deployability through systematic manipulation of geometric and material features.

Contact:  Jin Yang (jin.yang@austin.utexas.edu)