Study on Composite Tolerance Design and Optimization of a Turning Machine Spindle Box

Integration of the complementary fields of structural health monitoring in self-healing materials (SHM2) has the potential to transform the traditional engineering concepts of fail safe and damaged tolerant design. Structural health monitoring seeks to embed and automate sensing capabilities within structures to determine their state and to detect degradation or damage. Once degradation or damage is detected, additional decisions and potential action are required. Reducing operational envelopes can prevent further damage accumulation or catastrophic failure or repairs can be performed to correct the degradation. Typical repair requires active involvement of personnel and potentially down time. Self-healing materials seek to avoid maintenance needs and down time through the creation of structures and materials with an imbued capability to repair damage. Together SHM^ 2 has the potential to create a closed loop where damage is detected using embedded sensors and automated analysis that can then initiate self-healing. The highly structured and controlled nature of self-healing materials presents an opportunity to design structures that additionally support health monitoring capabilities. This paper presents recent research and results informing the design of shape memory alloy (SMA) fiber reinforced metal matrix composites (MMCs) to optimize self-healing capabilities and structural health monitoring (SHM^2). Fiber pull tests were performed to analyze the strength of the interface between the SMA fibers and matrix allowing for sizing to complement both composite design and healing capabilities. Analysis was performed to understand complex failure mechanisms occurring at the interface between detwinning shape memory alloys and the metal matrix. And novel composite design was performed to support both the self-healing and damage detection capabilities of the material structure.

The long-term goal of this ONR funded project is to facilitate the design of architected composites that play a key role in damage tolerant and resilient structures. The main emphasis is on developing new composite structures with improved performance and durability as compared to conventional structural composites. To that end, we will present our work in detail on the following within the realm of sandwich composites along with a novel Machine Learning framework for stress prediction in composites: 1) Novel recoverable sandwich composite structures: Traditional sandwich cores such as foam core or honeycomb structures are good options for enabling lightweight and stiff structures. Although, these cores are known to dissipate energy under extreme conditions such as impact loading, they experience permanent damage. Here, our goal is to design core structures that undergo substantial deformation without accumulating damage and recover their original geometric configuration after the loading is removed. In contrast to a traditional foam or honeycomb structure, we have developed a multi-layer architected core design that facilitates significant deformation beyond the initial peak load, yielding a larger energy dissipation during impact and other extreme loading scenarios. We utilize the concept of pseudo-bistability of truncated cone unit cells to achieve elastic buckling for energy dissipation and shape recovery of core structures. 2) Tailoring of sandwich composite facings: Our objective is to establish the influence of fiber architecture on moisture diffusion pathways in FRPC facings for enabling damage tolerant facing designs. To that end, we have evaluated the moisture kinetics in FRPCs by developing micromechanics based computational models within FEM. We have explained the effect of tortuous diffusion pathways that manifest within FRPCs due to internal fiber architectures. Finally, we established the relationship between tortuosity and diffusivity that can be used for studying moisture diffusion in other FRPCs.

Impact behaviour of fibre-reinforced composites Recent developments in impact damage assessment of fibre composites Modelling impact of composite structures using small specimens Impact damage - tolerant composite structural design Damage resistance and tolerance of thick laminated woven roving GFRP plates subjected to low-velocity impact Elastic impact stress analysis of composite plates and cylinders Impact behaviour and analysis of CFRP laminated plates Perforation of FRP laminates and sandwich panels subjected to missile impact High velocity impact damage to polymer matrix composites.

A review of toroidal composite pressure vessel optimisation and damage tolerant design for high pressure gaseous fuel storage

Damage tolerance of an impacted composite laminate

<div class="htmlview paragraph">Requirements, analysis methodologies, and selected test data for impact damage tolerance and fail-safety of composite sandwich panels are reviewed and discussed. Characteristic impact damage, failure modes, and residual strength prediction methodologies for impact damaged composite sandwich panels are presented, as well as guidelines for impact damage tolerant design. A tear strap design methodology for fail-safe composite sandwich panel design is discussed, along with pertinent residual strength test data for composite sandwich tear strap panels.</div>

The overall objective of this effort was to provide theoretical prediction for damage development for a set of laminated composites using Alpha STAR Corporations’ commercial code GENOA (GENeral Optimization Analyzer) for the Air Force Research Laboratory program entitled “Damage Tolerance Design Principles (DTDP)”. Damage progression and prediction for advance composite benchmarks were done under static and fatigue service loading using test data from Lockheed Martin Aeronautics and Air Force Research Laboratory. In the current paper, the results for the static analysis are presented. Emerging and innovative multi-scale (MS) modeling using computational structural mechanics and progressive failure analysis were proven to address the Air Force’s vision to perform predictive evaluation of composite materials using a building block validation strategy and certification process. Three layups were tested in tension and compression for unnotched and openhole configurations. Calibration of the fiber and matrix properties was performed using in plane, 3pt bend and DCB test data. After this, mesh convergence, solver selection based on CPU time, and mesh sensitivities was performed. The static blind simulations of strength showed an average error of 12.9% between simulation and the test data. For stiffness, the percent difference was found to be 23.5% on average. Although the focus was on the ability to blindly predict test data, recalibration efforts show an average of 9.2% difference between simulation and test for strengths and 12.4% for stiffness computations. Damage at ∼60–75% and ∼90% of max loading was comparable with X-ray observations of specimens set aside solely for that purpose. All simulations used the same set of inputs (constituents, voids, fiber waviness, etc.) except for the noted analysis setting differences between blind and recalibration simulations. The method is consistent and follows a building block simulation approach that has an advanced yet simplistic theoretical multi-scale progressive failure analysis approach all contained in the commercial GENOA software. The method was demonstrated to work having GENOA directly run sequential NASTRAN simulations and, post project completion, with the ABAQUS solver using GENOA as a material subroutine.

This paper reviews recent research on cement based composites design for damage tolerance. Specific focus is placed on the influence of fiber and interface properties on the complementary energy of the composite crack bridging behavior, which in turn governs the mechanics of composite fracture. The theoretical concepts are illustrated with examples of highly damage tolerant cement based composites containing fiber types with and without chemical interfacial bonds. The composite fracture and damage tolerant behaviors are rationalized with the mechanics of steady state cracking in fiber composites.

Lateral misalignment accompanied with rotational angle is unavoidable in the long-track dynamic wireless power transfer (DWPT) system. This results in an undesirable degradation in transmission performance. To address this vexing misalignment issue, a receiver (Rx) side topology based on multipolarity-coupling composite design is proposed in this article. The designed Rx composite assembly, consisting of a circular coil and three rectangular solenoid coils, effectively catches both vertical and horizontal magnetic fields, complementing each other to suppress mutual inductance variation during misalignment. Only two design variables are included for parameter optimization process, which features simple design flow and convenient implementation without resorting to changing the existing ground assembly configuration. Efficiency stability enhancement is unveiled through power loss analyses combined with theoretical calculation. A scaled-down long-track DWPT system with nearly 320 W output power is built as an example to validate the proposed design. The experimental results show that the system dc–dc efficiency variations remain below 10% with a 40 mm lateral misalignment (53% of the transmitter track width) across a full deflection angle range of [−90°, 90°].

The current emphasis within the composite design community is gradually shifting from achieving minimum weight designs at all costs to more cost-effective and damage tolerant structural designs. A damage tolerant structure must not only be able to effectively absorb energy locally at the point of damage initiation but must also be fail-safe. A very efficient way of designing a composite fail-safe structure is to provide it with the ability to arrest a potentially catastrophic crack by increasing its fracture resistance. The fracture behaviour of composites can be quantified by measuring its toughness and it can be broadly classified into interlaminar and intralaminar fractures. Most of the work reported in the recent literature has focused on the investigation of the interlaminar behaviour of composites with a limited number of works addressing the intralaminar fracture behaviour. The measurement of intralaminar toughness requires a pre-cracked specimen and in most cases, particularly for CFRP materials. Its determination can be based on the Linear Elastic Fracture Mechanics (LEFM) approach. Different types of specimens and crack geometries are currently available in the literature to characterise the intralaminar fracture behaviour of composites under pure mode I (Cowley & Beaumont, 1997; Konstantinos et al., 2005), mode II and mixed-mode loading (Lin & Shetty, 2003), however none of them are standardised. The specimen selection depends on the material system under investigation and expected toughness values range from initiation to propagation. It is also worth mentioning that most of these specimens were originally designed for fracture in isotropic materials. The poor performance of composites in shear and compression loading, compared to tension loading in the fibre direction may lead to failure prior to crack growth. Such restrictions impose limitations on their applicability and alternative specimen designs are needed. For mode-I, the Overheight Compact Tension (OCT) specimen has the advantage of promoting a stable crack growth which eventually enables the evaluation of both initiation and propagation values for the intralaminar toughness. Jose et al. (2001) investigated the mode I intralaminar toughness of carbon/ epoxy cross-ply laminates using overheight compact tension specimens. The experimental results were compared with finite element simulations using a modified crack-closure integral method and a methodology for calculating the stress intensity factor associated with matrix cracking and fibre fracture was presented. Based on the work by Jose et al. (2001), Pinho et al. (2006a) investigated the intralaminar toughness associated with fibre breakage in tension and fibre kinking in compression in unidirectional pre-preg composites using Compact Tension (CT)

Evaluation of toughening concepts at structural features in CFRP—Part I: Stiffener pull-off

Finite element modelling of bridging micro-mechanics in through-thickness reinforced composite laminates