Beams with controllable flexural stiffness

This study aimed to quantify the sensitivity of a thoracolumbar musculoskeletal model with a flexible thoracic spine and articulated ribcage to disc flexural stiffness variation inherent from in-vitro cadaveric data. The model was personalized to a normal weight subject, whose upper body segmental masses and centers of mass were computed using a body-shape-based approach. Joint flexural stiffness curves were defined based on in-vitro flexion-extension moment-rotation data from several specimens taken at various thoracic levels, with stiffness variation reaching 1.2 Nm/deg. Neutral standing and forward flexion postures were simulated using in-vivo measured spinal rhythm. The finding revealed negligeable sensitivity of joint reaction forces, less than 2.5% Body Weight (BW), to flexural stiffness in neutral standing posture. The sensitivity became more pronounced, especially at mid-level thoracic joints, with deviations reaching up to 14% BW and 26% BW for antero-posterior shear and compressive forces, respectively, in 60-degree forward flexion. Very low Root Mean Square Error (RMSE) and normalized RMSE values, calculated using intradiscal pressure based compressive forces, indicated no effects of flexural disc stiffness variation on model prediction validation. The findings underscored the importance of cautious consideration when utilizing flexural stiffness from a single cadaveric specimen.

BackgroundFlexural three-point bending tests are useful for characterizing the mechanical properties of plant stems. These tests can be performed with minimal sample preparation, thus allowing tests to be performed relatively quickly. The best-practice for such tests involves long spans with supports and load placed at nodes. This approach typically provides only one flexural stiffness measurement per specimen. However, by combining flexural tests with analytic equations, it is possible to solve for the mechanical characteristics of individual stem segments.ResultsA method is presented for using flexural tests to obtain estimates of flexural stiffness of individual segments. This method pairs physical test data with analytic models to obtain a system of equations. The solution of this system of equations provides values of flexural stiffness for individual stalk segments. Uncertainty in the solved values for flexural stiffness were found to be strongly dependent upon measurement errors. Row-wise scaling of the system of equations reduced the influence of measurement error. Of many possible test combinations, the most advantageous set of tests for performing these measurements were identified. Relationships between measurement uncertainty and solution uncertainty were provided for two different testing methods.ConclusionsThe methods presented in this paper can be used to measure the axial variation in flexural stiffness of plant stem segments. However, care must be taken to account for the influence of measurement error as the individual segment method amplifies measurement error. An alternative method involving aggregate flexural stiffness values does not amplify measurement error, but provides lower spatial resolution.

The organization of tissues in appendages often affects their mechanical properties and function. In the fish family Labridae, swimming behavior is associated with pectoral fin flexural stiffness and morphology, where fins range on a continuum from stiff to relatively flexible fins. Across this diversity, pectoral fin flexural stiffness decreases exponentially along the length of any given fin ray, and ray stiffness decreases along the chord of the fin from the leading to trailing edge. In this study, we examine the morphological properties of fin rays, including the effective modulus in bending (E), second moment of area (I), segmentation, and branching patterns, and their impact on fin ray stiffness. We quantify intrinsic pectoral fin ray stiffness in similarly sized fins of two closely related species that employ fins of divergent mechanics, the flapping Gomphosus varius and the rowing Halichoeres bivittatus. While segmentation patterns and E were similar between species, measurements of I and the number of fin ray branch nodes were greater in G. varius than in H. bivittatus. A multiple regression model found that of these variables, I was always significantly correlated with fin ray flexural stiffness and that variation in I always explained the majority of the variation in flexural stiffness. Thus, while most of the morphological variables quantified in this study correlate with fin ray flexural stiffness, second moment of area is the greatest factor contributing to variation in flexural stiffness. Further, interspecific variation in fin ray branching pattern could be used as a means of tuning the effective stiffness of the fin webbing to differences in swimming behavior and hydrodynamics. The comparison of these results to other systems begins to unveil fundamental morphological features of biological beams and yields insight into the role of mechanical properties in fin deformation for aquatic locomotion.

We present the results of investigation of flexible stiffness of multilayer beams with geometric and/or stiffness asymmetry. An algorithm is proposed for the evaluation of coordinates of the geometric and stiffness centers and the analysis of flexural stiffness in any direction and its extreme values in multilayer beams with asymmetry of any kind. We study the kinetics of coordinates of the geometric and stiffness centers and flexural stiffness depending on the behavior of the geometric parameters and the ratio of the moduli of elasticity of layers and the cross-sectional shape of a multilayer beam.

Flexural behavior of FRP and steel reinforced glulam beams: Experimental and theoretical evaluation

The composite slim beam has become popular throughout Europe in recent years and has also been used on some projects in China. With its steel section encased in a concrete slab, the steel-concrete composite slim beam can provide the floor construction with minimum depth and high fire resistance. However, the design method of the T-shape steel-concrete composite beam is no longer applicable to the composite slim beam with deep deck for its special construction, of which the present design models are not available but mainly depend on experiences. The elevation of the flexural stiffness and bending capacity of composite slim beams with deep deck is rather complicated, because the influences of many factors should be taken into account, such as the variable section dimensions, development of cracks and non-linear characteristics of concrete, etc. In this paper, experimental investigations have been conducted into the flexural behavior of two specimens of simply supported composite slim beam with deep deck. The emphases were laid on the bonding force on the interface between steel beam and concrete, the stress distribution of beam section, the flexural stiffness and bending capacity of the composite beams. Based on the experimental results, the reduction factor of equivalent stress distribution in concrete flange is suggested, and the calculation method of flexural stiffness and bending capacity of simply supported slim beams are proposed.

Ultra-high-performance geopolymer concrete (UHPGC) emerges as a sustainable and cost-effective alternative to Portland cement-based UHPC, offering similar mechanical properties while significantly reducing carbon footprint and energy consumption. Research on UHPGC components is extremely scarce. This study focuses on the flexural and crack behavior of UHPGC beams with different steel fiber contents and longitudinal reinforcement ratios. Five UHPGC beams were tested under four-point bending. The test results were evaluated in terms of the failure mode, load–deflection relationship, flexural capacity, ductility, average crack spacing, and short-term flexural stiffness. The results show that all the UHPGC beams failed due to crack localization. Increases in the reinforcement ratio and steel fiber content had favorable effects on the flexural capacity and flexural stiffness. When the reinforcement ratio increased from 1.18% to 2.32%, the flexural capacity and flexural stiffness increased by 60.5% and 12.3%, respectively. As the steel fiber content increased from 1.5% to 2.5%, the flexural capacity and flexural stiffness increased by 4.7% and 4.4%, respectively. Furthermore, the flexural capacity, flexural stiffness, and crack spacing of the UHPGC beams were evaluated using existing methods. The results indicate that the existing methods can effectively predict flexural capacity and flexural stiffness in UHPGC beams but overestimate crack spacing. This study will provide a reference for the structural design of UHPGC.

The aim of this paper is to assess the structural behavior of hybrid thin‐walled beams which were fabricated using laminated carbon fiber reinforced polymer (CFRP). Seven hybrid (CFRP) I‐beams were fabricated, instrumented, then have been tested under monotonic four‐point loading in order to evaluate their behavior up to failure. In constructing the I‐beam specimens which were evaluated in this study, plywood core was implemented on both the web and flanges. Several important parameters were conducted in this study considering changing both of the ply orientations and stacking sequences of laminated fibers, also changing the shear span‐to‐depth ratio (a/d) of the specimens. The experimental results showed that stacking sequence is the most significant parameter that influences both flexural strength and stiffness of the hybrid beams. Also, the experimental results promoted the effectiveness of the core material for enhancing the flexure (bending) stiffness of beams. Then, these results were compared with a previous simulated study which used the finite element modeling to model the beams. Also, in order to evaluate the efficiency of the CRFP beams, the results were compared to similar steel beams having the same dimensions of the CFRP beams. As compared to steel beams, the load carrying capacity of the laminated beams is being high compared with steel beams when taking into consideration their specific strength ratio.

To reduce the self-weight of bamboo-concrete composite (BCC) beams and realize rapid industrial production, innovative assembled bamboo-lightweight concrete composite (ABLCC) beams are presented for use in engineering structures. To verify the structural performance of the ABLCC beams, a series of bending tests were performed on the bamboo beams, the cast-in-place bamboo-lightweight concrete composite (PBLCC) beams and the ABLCC beams. The effects of the thickness of the perforated steel plate, the connector spacing, and the construction technology on the BCC beams were investigated. The test results showed that the failure mode of the ABLCC beams was bamboo fiber cracking at the bottom of the mid-span. Compared with the benchmark bamboo beams, the bending capacity and stiffness of the ABLCC beams increased by 1.43–1.94 times and 2.20–4.16 times, respectively. Compared with the cast-in-place bamboo-lightweight concrete composite (PBLCC) beams, the bending capacity of the ABLCC beam was essentially the same, and the flexural stiffness increased by 1.18 times. The bending capacity, flexural stiffness and combination efficiency of the ABLCC beam increased with decreasing connector spacing. The increase in the thickness of the perforated steel plate did not have a substantial effect on the flexural stiffness of the ABLCC beam. Analytical and numerical methods were validated against the experimental results.

Several batches of reinforced concrete (RC) and prestressed reinforced concrete (PRC) beams with 500MPa steel bars were tested in Tongji University, recently. The results indicated that the development of flexural stiffness after concrete cracking was influenced mainly by three parameters including initial elastic flexural stiffness, longitudinal reinforcement ratio and load level. Based on our 20 years' systematic research on crack and stiffness, a simpler unified formula is suggested after theoretical analyses for predicting short term flexural stiffness of concrete beams using high strength steel bars. Comparison with calculations from different codes at home and abroad exhibits that the suggested formula is precise and practical for both RC and PRC beams.

Solid-state complexes of flexible polymers with surfactants (surf) exhibit mesomorphic phase and microphase-separated lamellar morphology. Because the surf molecules are strongly associated with the polymer backbone, the ordered packing of the alkyl tails should be cooperative with the chain packing in the polymer layers which is influenced by chain topology. In this study, the supramolecular structure and thermal properties of the complexes of a highly branched poly(ethylenimine) (PEI) with dodecylbenzenesulfonic acid (DBSA) were investigated. Polarized optical microscopy and small-angle X-ray scattering (SAXS) revealed the presences of mesomorphic phases and microphase-separated lamellar morphology in the complexes. The ordered supramolecular structure was observed not only for the stoichiometric composition but over a wide composition range. The thicknesses of polymer and surf layers were determined from the one-dimensional correlation function. The surf layer thickness varied with complex composition. The glass transition temperature of polymer layers was raised by complexation because of the stiffening of polymer chains. Complexation with DBSA also enhanced the thermal stability of PEI, where the thermal decomposition temperature can be raised by as much as 50 °C.

Laser Raman spectroscopy is an effective tool for the study of biodegradable polymers, which play a vital role in the new developments in coronary implants such as stents. There is much excitement around the potential capabilities of synthetic biodegradable polymers and the effect they will have on the design and function of implanted devices. In the present investigation, heparin‐conjugated biodegradable copolymers were evaluated for their durability as drug‐eluting stent coatings. Laser Raman spectroscopic studies were carried out and spectra recorded and analyzed of explanted stents coated with different amounts of polymer alone, showing the existence of different levels at different quantities of polymer. The polymer was detected on every stent analyzed. On the stents coated with a thick layer of polymer, a firm layer of polymer still existed on the stent. In contrast, this layer was degraded and spread around on the stents coated with only a thin layer of the polymer. This indicates that the polymers used in the stents in the present investigation exhibit acceptable biodegradability. Such polymers can be used as efficient drug carriers, as these materials show good degradation after the stipulated period. Copyright © 2009 John Wiley & Sons, Ltd.

Metal fused filament fabrication (MF3) is a simple and cost-effective additive manufacturing method for generating three-dimensional (3D) metal-based products. In this study, three models were developed individually using a combination of metal and polymer materials with varying layer thicknesses in the radial direction. The specimen model has been developed with five layers where the consecutive layers were prepared with metal and polymer. Obviously, the thickness of the polymer layer increased in each model. The main objective of this work is to confirm the penetration of temperature from one layer to another when debinding through a metal and polymer interlayer stack. Furthermore, the temperature distribution, total heat flux and directional heat flux were investigated in relation to the polymer layer thickness. As a result, the model created with the polymer layer thickness obtained the largest range of temperature distribution (450.15°C), directional heat flux (6206.4 W/m2) and total heat flux (7845.6 W/m2). Thermal analysis clarified the various materials connecting along with the radial direction of the model in order to confront the debinding procedure for converting the model into a physical object. These findings were anticipated to aid in the fabrication of the actual 3D component utilising the MF3 technique in the future.

Property-map of epoxy-treated and as-printed polymeric additively manufactured materials

Flexural behavior of alkali-activated slag-based concrete beams