This paper focuses on the processing, fabrication and characterization of a novel carbon nanotube (CNT) based electroactive shape memory epoxy nanocomposite with significant improvements in static ...and dynamic mechanical properties. Electro-active shape memory specimens have been fabricated by soaking CNT membranes (buckypaper) in shape memory epoxy polymer (SMEP) through a specialized fabrication process developed in-house that results in a high CNT wt. fraction of 30 wt%. The novel fabrication approach leads to drastic improvement in mechanical performance due to effective interfacial interaction between the SMEP and CNTs at the nanoscale. This is accomplished as the SMEP thoroughly permeates the buckypaper through the nano- and micro-pores, owing to the microstructure-induced capillary action. The improvement in quasistatic and dynamic mechanical properties of the baseline SMEP using CNT buckypaper is demonstrated and correlated with the microstructure through scanning electron microscopy characterization. For the buckypaper-enhanced SMEP (CNT-SMEP), the improvement in elastic modulus in the temperature extremes of 20 and 50ׄ°C was found to be 52% (1810 MPa compared to 2740 MPa) and 514% (7.6 MPa compared to 46.7 MPa), respectively. Furthermore, through the dynamic mechanical measurements, the increase in storage modulus in the range of 30-90ׄ°C was found to be 60% and 82%, respectively. In addition, the shape memory recovery response for this material system is characterized by stress-free electrical actuation of the CNT-SMEP using a 12V DC supply as well as using stress and temperature control testing.
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•Electro-active shape memory using buckypaper through novel fabrication process.•High CNT wt.% of 30 wt% in shape memory epoxy.•Elastic modulus increase 20–50ׄ°C range found to be 52% and 514%, respectively.•Storage modulus increase in range of 30-90ׄ°C found to be 60% and 82%, respectively.
This work focuses on high-cycle fatigue and quasi-static tensile performance of additively manufactured and wrought 17–4 stainless steel. Test specimens were manufactured using a Markforged Metal X ...printer via the atomic diffusion additive manufacturing process or machined from commercial stock. High-cycle fatigue testing showed that wrought specimens could sustain higher loads at 10
6
cycles (565 MPa) as compared to additively manufactured specimens with solid infill (216 MPa) and triangular infill (136 MPa). The mass-normalized fatigue responses of the additively manufactured specimens were similar when comparing in-fill type while wrought specimens performed roughly 50% better across the range from 10
4
to 3.5 × 10
7
cycles.
This work focuses on characterization of the mechanical performance of additively manufactured fiberglass and carbon fiber–reinforced composites fabricated with varying amounts of fiber content using ...a Markforged X7 printer. Samples were subjected to tension and three-point bending tests, evaluating the nominal increase in those properties per unit cost in dollars and mass. Samples were also scanned using X-ray computed micro tomography (µCT) to characterize their internal structure. Test results showed that the tensile strength and stiffness of carbon fiber–reinforced samples improved with each increase in fiber volume fraction (
V
f
), while fiberglass-reinforced samples showed diminishing returns above a
V
f
of 22.3%. The bending strength and stiffness of carbon rose monotonically with every increase in
V
f
and plateaued for fiberglass above a
V
f
of 17.8%. Carbon outperformed fiberglass in both tension and bending stiffness per gram. Carbon had a much higher tensile stiffness per dollar than fiberglass, while the bending stiffness per dollar of both fiber types plateaued above a
V
f
of 5.2% for fiberglass and 6.5% for carbon. µCT analysis showed considerable void content with a lower average void fraction (
V
v
) for fiberglass than for carbon. The
V
v
of fiberglass decreased with increasing
V
f
, while the opposite was true for carbon.
The goal of this work is to understand the underlying mechanisms that govern shape memory of polymer nanocomposites at the molecular level and to utilize them for novel synthetic shape memory polymer ...(SMP) materials for reconfigurable structures. In this study, we have performed coarse-grained molecular dynamics simulations of buckypaper (BP)/epoxy nanocomposites with a focus on their mechanical and shape memory performances, specifically on prediction of the Young's modulus of the material as a function of carbon nanotube (CNT) loading. Our results demonstrate that the Young's modulus linearly increases with CNT volume fraction below 0.16 (40 wt%) followed by a sharp upsurge of the modulus at higher loading where the onset of entanglements of nanotubes was determined. Additionally, we found a significantly greater increase of the modulus at T>Tg compared with the values below the glass transition temperature Tg for all considered systems. The simulation suggests that incorporation of BP restricts relaxation of network strands of the polymer matrix and leads to resistance in the recovery process of composites.
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•Shape memory and mechanics of polymer nanocomposites are studied at molecular level.•Coarse-grained molecular dynamics of buckypaper/epoxy predicts the Young's modulus.•The Young's modulus steeply increases at the onset of entanglements of nanotubes.•Significantly greater increase of the modulus is observed above the glass transition.•Incorporation of buckypaper leads to resistance in recovery process of composites.
The mechanical properties of a unidirectional carbon-fiber reinforced polymer (CFRP) laminate with Cu mesh layers were investigated for use in aerospace applications as a multifunctional structural ...and electromagnetic interference shielding component. Nanoindentation was used to study the fiber/PEEK and Cu/PEEK interfaces. A data analysis methodology is presented to assess the interfacial strength from plots of hardness and modulus versus distance from fiber/Cu edge. The results indicated that annealing resulted in enhanced adhesion at the fiber/PEEK interface. Additionally, indents near the Cu/PEEK interface indicated poor interfacial adhesion. Bulk mechanical testing was performed to determine the effect of adding Cu mesh layers on the mechanical properties of the laminate. Additional Cu mesh layers decreased the tension, shear, and bending strength/modulus, while the open hole compression strength increased. This indicates that the Cu/PEEK interfaces weaken the laminate and lower the tension, shear, and bending strength by delamination.
Many active materials have properties that make them challenging to design with or limit their utility, including having combinations of nonlinear, viscous, slow, or small responses. In this work, we ...show that by designing metamaterial unit cells that have separately active and, specifically geometrically nonlinear, passive elements, many of these drawbacks can be mitigated and enhanced performance enabled (specifically, large, rapid, and resettable shape change). This separation between active and passive elements is advantageous, in that the complex active materials can be assigned only where needed, with the simplest geometries and functions. The use of geometric nonlinearity in passive elements is helpful as it provides mechanisms for augmented performance and further simplifies the role of the active elements. While all elements of the microstructural motifs used herein have been previously seen elsewhere, we suggest that the contribution provided here is a conceptual design approach that may be used more broadly for enabling new types of high-performing, stimuli-responsive metamaterials.
Purpose There is a lack of information evaluating specific markers of performance in patients awaiting bariatric surgery. We aimed to assess the postural control, functional performance, strength and ...endurance performance for morbidly obese patients awaiting bariatric surgery compared to lean controls. Subjects and Methods All parameters were assessed by modified Y-balance test, timed-up-and-go-test, maximum strength testing on resistance exercise equipment and cardio-pulmonary exercise testing on a cycle ergometer in 10 morbidly obese patients awaiting bariatric surgery and 10 age- and sex-matched lean controls. Results It was found that significant differences existed for overall modified Y-balance test in morbidly obese patients awaiting bariatric surgery versus lean controls (0.37 ± 0.03 vs. 0.47 ± 0.02 cm.cm−1), timed-up-and-go-test (9.33 ± 1.23 vs. 7.85 ± 1.73 sec) and several variables of cardio-pulmonary exercise testing. Overall absolute strength expressed in kilogram was similar, yet when relativized to body weight strength differences were notable (0.4 ± 0.17 vs. 0.83 ± 0.32 kg.kg−1). Conclusion The results of this study demonstrate the need for comprehensive functional assessment prior to surgery with an identified demand for subsequent tailored physical training prescription that should begin before surgery.
In this work, we present a novel approach for improving the delamination resistance and durability of structural composite laminates using compliant thermoplastic polyurethane (TPU) interlayers that ...allow decoupling of the structural plies within the laminate thus preventing catastrophic delamination. Laminates with different compliant interlayer thicknesses are fabricated and characterized under multiple low velocity impacts (LVI) to demonstrate the significant improvement in delamination resistance that can be achieved. Finite element analysis and experimental data on samples of the interlayer laminates subjected to three-point bending is presented to provide additional insight into the unique decoupling phenomena enabling significant improvements in delamination resistance of structural composite laminates.
Objective To examine the relation of radiographic features of osteoarthritis to knee pain in people with knees discordant for knee pain in two cohorts.Design Within person, knee matched, case-control ...study.Setting and participants Participants in the Multicenter Osteoarthritis (MOST) and Framingham Osteoarthritis studies who had knee radiographs and assessments of knee pain.Main outcome measures Association of each pain measure (frequency, consistency, and severity) with radiographic osteoarthritis, as assessed by Kellgren and Lawrence grade (0-4) and osteophyte and joint space narrowing grades (0-3) among matched sets of two knees within individual participants whose knees were discordant for pain status.Results 696 people from MOST and 336 people from Framingham were included. Kellgren and Lawrence grades were strongly associated with frequent knee pain—for example, for Kellgren and Lawrence grade 4 v grade 0 the odds ratio for pain was 151 (95% confidence interval 43 to 526) in MOST and 73 (16 to 331) in Framingham (both P<0.001 for trend). Similar results were also seen for the relation of Kellgren and Lawrence scores to consistency and severity of knee pain. Joint space narrowing was more strongly associated with each pain measure than were osteophytes.Conclusions Using a method that minimises between person confounding, this study found that radiographic osteoarthritis and individual radiographic features of osteoarthritis were strongly associated with knee pain.
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