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Mechanical properties are essential for the biological activities of cells, and they have been shown to be affected by diseases. Therefore, accurate mechanical characterization is important for studying the cell lifecycle, cell-cell interactions, and disease diagnosis. While the cytoskeleton and actin cortex are typically the primary structural stiffness contributors in most live cells, oocytes possess an additional extracellular layer known as the vitelline membrane (VM), or envelope, which can significantly impact their overall mechanical properties. In this study, we utilized nanoindentation via an atomic force microscope to measure the Young's modulus of Xenopus laevis oocytes at different force setpoints and explored the influence of the VM by conducting measurements on oocytes with the membrane removed. The findings revealed that the removal of VM led to a significant decrease in the apparent Young's modulus of the oocytes, highlighting the pivotal role of the VM as the main structural component responsible for the oocyte's shape and stiffness. Furthermore, the mechanical behavior of VM was investigated through finite element (FE) simulations of the nanoindentation process. FE simulations with the VM Young's modulus in the range 20–60 MPa resulted in force-displacement curves that closely resemble experimental in terms of shape and maximum force for a given indentation depth. 

ABSTRACT Engaging students in hands-on activities and providing out-of-school experiences have been shown to improve academic performance and spark interest in science. Our interdisciplinary team developed a workshop for middle and high school students as part of a summer program at a Hispanic-serving institution in southern New Mexico. The goal was to foster interest and readiness for science, technology, engineering, and mathematics careers and college entry. The workshop introduced students to viscoelasticity, a key concept in biophysics that describes the mechanical behavior of biological tissues, which is vital for understanding their structural and functional properties under various physical forces and conditions. The curriculum included a presentation, a discussion linking mechanical properties with biology, and hands-on experiments that demonstrated viscoelastic principles. Pre- and postworkshop surveys assessed students’ experiences and understanding of the material. Analysis revealed that students could relate the concepts to their daily lives, gained a basic understanding of mechanical properties, and found at least one experiment enjoyable and interesting. 

3D woven composites are well known for their high strength, dimensional stability, delamination, and impact resistance. They are often used in aerospace, energy, and automotive industries where material parts can experience harsh service conditions including substantial variations in temperature. This may lead to significant thermal deformations and thermally-induced stresses in the material. Additionally, 3D woven composites are often produced using resin transfer molding (RTM) technique which involves curing the epoxy resin at elevated temperatures leading to accumulation of the processing-induced residual stress. Thus, understanding of effective thermal behavior of 3D woven composites is essential for their successful design and service. In this paper, the effective thermal properties of 3D woven carbon-epoxy composite materials are estimated using mesoscale finite element models previously developed for evaluation of the manufacturing-induced residual stresses. We determine effective coefficients of thermal expansion (CTEs) of the composites in terms of the known thermal and mechanical properties of epoxy resin and carbon fibers. We investigate how temperature sensitivity of the thermal and mechanical properties of the epoxy influences the overall thermal properties of the composite. The simulations are performed for different composite reinforcement morphologies including ply-to-ply and orthogonal. It is shown that even linear dependence of epoxy’s stiffness and CTE on temperature results in a nonlinear dependence on temperature of the overall composite’s CTE. 

Manufacturing-induced residual stresses in carbon/epoxy 3D woven composites arise during cooling after curing due to a large difference in the coefficients of thermal expansion between the carbon fibers and the epoxy matrix. The magnitudes of these stresses appear to be higher in composites with high throughthickness reinforcement and in some cases are sufficient to lead to matrix cracking. This paper presents a numerical approach to simulation of development of manufacturing-induced residual stresses in an orthogonal 3D woven composite unit cell using finite element analysis. The proposed mesoscale modeling combines viscoelastic stress relaxation of the epoxy matrix and realistic reinforcement geometry (based on microtomography and fabric mechanics simulations) and includes imaginginformed interfacial (tow/matrix) cracks. Sensitivity of the numerical predictions to reinforcement geometry and presence of defects is discussed. To validate the predictions, blind hole drilling is simulated, and the predicted resulting surface displacements are compared to the experimentally measured values. The validated model provides an insight into the volumetric distribution of residual stresses in 3D woven composites. The presented approach can be used for studies of residual stress effects on mechanical performance of composites and strategies directed at their mitigation. 

The focus of this paper is application of a Graphical Processing Unit (GPU) based solver to linearly elastic finite element analysis (FEA) of composites with threedimensional (3D) woven reinforcements. Aspects specific to this material system including local material orientations, high contrast between elastic properties of constituents, large number of degrees of freedom, and simulation runtimes are discussed. Speedups offered by parallelization via GPUs and regularity of structured grids enable matrix-free implementation of FEA, which requires reassembly of the global stiffness at every iteration of solution of the system of linear equations, but in turn significantly reduces memory requirements. This makes linear analysis of composite structures with explicit reinforcement representation (tens of millions of degrees of freedom) possible on personal computers. Potential applications of this procedure include fast calculation of effective properties for design of novel 3D woven architectures and efficient solution of problems with high degrees of material nonlinearity requiring frequent stiffness matrix updates. 

3D woven carbon/epoxy composites are often produced using resin transfer molding technique which includes epoxy curing at elevated temperatures. The process may lead to accumulation of the intrinsic residual stresses during cooling of the material caused by the mismatch between carbon and epoxy coefficients of thermal expansion. This paper deals with implementation of mesoscale finite element models to evaluate intrinsic residual stresses in 3D woven composites. The stresses are determined by correlation of the surface displacements observed after drilling 1-mm diameter blind holes with the corresponding predictions of the models. We investigated how a numerical representation of the composite plate surface affects the correlation between the experimental measurements and numerical predictions and how it influences the evaluation of the process-induced residual stresses. It has been shown for ply-to-ply woven composites with different pick spacing that the absence of the resin layer leads to more accurate interpretation of the experimental measurements. The prediction of the average residual stress in the matrix phase of the composite was found to be sensitive to the surface representation accuracy, however, the residual stress magnitude and distribution was not affected fundamentally. 

Three panels of 3D woven carbon fiber/RTM6 epoxy composites with a ply-to-ply weave with 12x12 (warp/weft) picks per inch (ppi), 10x12 ppi, and 10x8 ppi were fabricated by resin transfer molding. Realistic finite element models of each weave architecture were constructed using Dynamic Fabric Mechanics Analyzer. The resin properties were isotropic and linear elastic and dependent on temperature. The resin-infiltrated fiber tow properties were estimated using homogenization based on Hashin and Shapery formulas. The model was considered to be at zero stress at the 165C curing temperature. The stresses resulting from cooling the composite to 25C were estimated using the resin temperature-dependent properties and the temperature independent properties of the tows. The displacement fields resulting from holes drilled through the middle of the top warp or weft yarn were estimated by virtually drilling a hole in the finite element model and were measured on the specimens using electronic speckle pattern interferometry. In general, the measured displacements transverse to the yarn were lower than the predicted displacements. This suggests the resin in the infiltrated yarns relieves some of the stress by permanently deforming during cooling. The measured displacements along the yarn were approximately the same for the 12x12 ppi,, lower for the 10x12 ppi, and significantly higher for the 10x8 ppi.