Significant Improvement In Stiffness Research Articles

Mechanical properties of porous Si3N4–SiC composites fabricated at 1200 °C

Porous Si3N4–SiC composites are potentially very attractive for various advanced applications such as aerospace and solar thermal power plants. However, processing of these porous composites is difficult and expensive due to the requirement of very high temperatures. In the present work, porous Si3N4–SiC composites were fabricated at only 1200 °C using phosphoric acid both as a pore former and binder. Porous composites with a constant SiC content were fabricated using various H3PO4 content and the morphology and mechanical properties of the porous composites were systematically investigated. The addition of SiC particles resulted in significant improvement of stiffness, compressive strength, and flexural strength over monolithic porous Si3N4, and porous composites fabricated using 40 vol% H3PO4 yielded the best properties of longitudinal elastic constant >50 GPa, flexural strength >80 MPa, and compressive strength >180 MPa. The achieved mechanical properties have been discussed in light of the analytical micromechanical models for Young's modulus and minimum solid area theory. Finally, the influence of processing temperature on the evolution of porosity and crystalline phases has been systematically studied and the dependence of porous composites' stiffness on these parameters has been investigated in detail.

All-scale approach to evaluate the elasticity and strength of carbon-allotrope reinforced polyimide

This computational study conducts a comprehensive all-scale analysis to predict the mechanical behavior (elasticity and strength) of polyimide matrices (Kapton®) reinforced with carbon nanostructures, spanning nanoscale, microscale, mesoscale, and macroscale. Representative volume elements at each scale undergo tensile and shear loadings to extract mechanical properties. Homogenization techniques are applied to transition between scales, considering these properties. Two nanostructures (graphene and γ-graphyne) are explored as reinforcements, evaluating the influence of volume fraction and orientation on composite mechanical properties. Results are validated through comparison with theoretical, computational, and experimental studies. Composite materials exhibited significant improvements in stiffness (up to 44% at a volume fraction of 0.5%) and tensile strength (up to 25% at a volume fraction of 0.5%) compared to the pristine polymeric matrix.

An isogeometric analysis of functionally graded triply periodic minimal surface microplates

In the current study, we present an efficient and straightforward numerical framework for exploring the responses of functionally graded triply periodic minimal surface (FG-TPMS) microplates. FG-TPMS structures including Primitive (P), Gyroid (G), and I-graph and Wrapped Package-graph (IWP) exhibit numerous potential applications in engineering due to their excellent stiffness-to-weight ratios. The behaviors of these structures at the microscale level, however, remain strongly unknown. For the first time, the static bending, free vibration and buckling characteristics of FG-TPMS microplates under various conditions are thoroughly presented in this study. To obtain this, this study employs the four-variable refined plate theory (RPT) with the support of the isogeometric analysis (IGA) to study these mechanical responses. Additionally, one material length scale parameter is utilized to account for the size effect with the modified couple stress theory. The two-phase fitting technique is adopted to predict the effective elastic properties of the FG-TPMS architectures. We in this research examine the two density distribution patterns in terms of the thickness for static bending, free vibration, uni-axial, and bi-axial buckling problems. The results of this investigation agree that as the material length scale parameter increases, the stiffness of microplate models improves significantly. It is explored that the effect of this size-dependent parameter also varies among different TPMS types. The FG microplates based on the P-type architecture have a trend of significant improvement in stiffness with a higher value of the material length scale ratio. With these findings, this research contributes to the development as well as the application of TPMS geometry in microscale structures in the future.

Fabricating PTFE nanocomposites via in situ filling of hydroxyapatite nanowires and their tribological performance

Excellent tribological performance and biocompatibility are required for the biomaterials that can be used for artificial acetabular cups. Hydroxyapatite nanowires, herein, were in situ filled into PTFE, and the resulting PTFE nanocomposites presented a high dispersion degree and a reliable interface adhesion. There were significant improvements in stiffness, heat-resistant and hydrophobic capabilities observed. It was observed that there were drastically decreased coefficients of friction and volume wear rates, which were determined by a sliding friction against a high-speed steel ring in the presence of simulated body fluid, and less and shallower plough furrows on the worn surfaces of the in situ fabricated nanocomposite specimens. The enhancements in tribological performance might be attributed to the one-dimensioned hydroxyapatite nanowires with the characteristics of both nano- and micro-sized materials and outstanding properties in mechanics, thermology, tribology. And the in situ fabrication method contributed to a reliable stress transfer between the matrix and the nanofillers, and led to a marked enhancement in stiffness, wear resistance and friction reduction of the nanocomposites fabricated with respect to the pristine PTFE even at a mass fraction of as low as 0.5%. The fabrication method and the resulting PTFE nanocomposites may suggest a way to a promising application in acetabular cups or other artificial joints/human tissues. • PTFE composites are fabricated via in situ filling of hydroxyapatite nanowires. • The nanofillers present a high dispersity and a reliable interface combination. • Mechanical, thermal and tribological properties are improved by in situ filling. • In situ filling contributes to dispersion, interfacial adhesion, and stress transfer. • Filler characteristics and fabrication method impart enhanced tribological performance.

Numerical and experimental investigations of novel nature inspired open lattice cellular structures for enhanced stiffness and specific energy absorption

Lattice structures are meant for light weight structure with a high strength to weight ratio used to carry high loads and high energy absorption capabilities. In the lattice structures, the non-stochastic arrangement of members has the ability to control and customize their mechanical properties. The recent developments in additive manufacturing provides freedom in design and gives flexibility to manufacture tailored complex novel lattice structures. In the present investigation, the traditional 2.5D honeycomb and the tessellated open lattice structures with basic crystalline arrangements of the members are considered to study the load carrying capacity, stiffness and energy absorption capabilities by keeping constant volume for each lattice. The results through the experiments and finite element analysis are compared with a novel open lattices structure to show significant improvement in stiffness and high energy absorption with the volume of the material. However, the novel open lattice structure has displayed prominent post yield plateau stresses and energy absorption with sacrificing stiffness and strength significantly.

U-shaped ferrocement wrapping with inter-surface locking for flexural strengthening of RC beam

ABSTRACTThis study aimed to evaluate the flexural performance of RC beam strengthened with u-shaped ferrocement wrapping and inter-surface locking. Total 12 numbers of RC beams were prepared and tested under third point loading. Three options viz. (i) u-shaped ferrocement wrapping with inherent cementitious bonding, (ii) u-shaped ferrocement wrapping with epoxy bonding and (iii) u-shaped ferrocement wrapping with epoxy and screw bonding were explored for strengthening of RC beam. The first cracking load, load–deflection behaviour, stiffness, energy absorption and the crack patterns were compared between the control and strengthened beams. It was found that the u-shaped ferrocement wrapping with inherent cementitious bonding increases the average flexural capacity up to 19.17% which further increased up to 41.29% by improving the inter-surface locking between the ferrocement layer and the original beam surfaces. The strengthened beam gave up to 35.58% less deformation for the same load compared to the control beam when the inter-surface locking was improved by applying epoxy and screw together. On the other hand, a significant improvement in stiffness and energy absorption capacity was obtained through strengthening with various inter-surface locking. At the maximum test load, all beams showed flexural cracks without any sign of debonding of ferrocement. From this study it could be concluded that u-shaped ferrocement wrapping effectively enhances the flexural capacity of RC beam and this could be further increased by improving the inter-surface locking between ferrocement wrapping and original concrete surface of RC beam.

Strengthening of RC Beams Using Lightweight Self-compacting Cementitious Composite

Repair and strengthening of reinforced concrete (RC) members in existing structures are very important to extend their service life. In this study, steel fiber reinforced high strength lightweight self-compacting concrete (SHLSCC) developed by the authors is applied for the strengthening of RC beams to improve their bending moment capacities. There are significant improvements in stiffness of strengthened beams as well as 14 - 58% improvements in peak load when strengthened with 40mm, 50mm and 60mm layers of SHLSCC. Application of SHLSCC in lower half (tension zone) of the beam increased its peak load by 33.1%. Results indicate that the material may effectively be utilized for strengthening of bending members in existing structures.

Strengthening of RC beams using steel fiber reinforced high strength lightweight self-compacting concrete (SHLSCC) and their strength predictions

Repair and strengthening of reinforced concrete (RC) members in existing structures are very important to extend their service life. Strain hardening cementitious composite developed by addition of steel fibers to concrete may be utilized for strengthening of existing structures. In this study, steel fiber reinforced high strength lightweight self-compacting concrete (SHLSCC) developed by the authors is applied for the strengthening of RC beams to improve their bending moment capacities. There are significant improvements in stiffness of strengthened beams as well as 14–58% improvements in peak load when strengthened with 40mm, 50mm and 60mm layers of SHLSCC. Application of SHLSCC in lower half (Tension zone) of the beam increased its peak load by 33.1%. Further, developed stress distribution models are effectively applied for the prediction of enhanced moment capacities of the strengthened beams. Comparison of experimental results with those calculated from the models showed maximum variation of 4%. The outcomes of this study will be very helpful in applying the modelled observations to in-situ structures allowing timely completion of repair and strengthening strategies.

Investigation of mechanical impact behavior of short carbon-fiber-reinforced PEEK composites

This paper describes the results of an experimental and numerical investigation of the impact behavior of short carbon fiber reinforced polyether-ether-ketone (SCFR PEEK) composites. The biocompatibility of PEEK and its short fiber composites, their rapid processing by injection molding and suitability for modern imaging have supported technological advances in prosthetic implants used in orthopedic medicine. Surgical implants, including hip and cranial implants, can experience clinically significant impact loading during medical installation and useful life. While the incorporation of short fibers in a thermoplastic matrix can produce significant improvements in stiffness and strength, it can also cause a marked reduction in ductility, making study of their energy absorption capability essential. In this work, the mechanical impact behavior of PEEK composites reinforced with polyacrylonitrile (PAN) short carbon fibers 30% in weight is compared with unfilled PEEK. The perforation tests conducted covered an impact kinetic energy range from 21J to 131J, equivalent to the range observed in a fall, the leading cause of hip fractures. Energy absorption capability, damage extension and failure mechanism have been quantified and reported. A numerical modeling that includes homogenization of elastic material and anisotropic damage is presented and validated with experimental data. At all impact energies, SCFR PEEK composites showed a brittle failure and their absorption energy capability decreases drastically in comparison with unfilled PEEK.

On the mechanical properties of hierarchical lattices

Hierarchical lattices are made of finer lattices in successive smaller scales. This paper analytically studies the effect of hierarchy on the stiffness and strength of self-similar and hybrid type lattices, made by combining two distinct variants of topologies, governed by the bending and stretching dominated architectures. Scaling argument and physical reasoning are used to explain the behaviour of these lattices. The results show that the in-plane stiffness and the elastic buckling strength of the bending–bending lattices progressively improve with hierarchy; in contrast, only the buckling strength improves substantially for the stretching–stretching lattices, while the stiffness decreases. Low density bending–stretching lattices are unique with a significant improvement in stiffness, buckling, plastic collapse or crushing strength with hierarchy, whereas the stretching–bending lattices exhibit flexibility with lower strength. Despite no gain in stiffness, substantial gain in out-of-plane compressive strength is obtained with hierarchy because of the enhanced elastic and plastic buckling strength. Thus the advantage of combining lattices at multiple length scales provides a wide spectrum of choices for tailoring the properties for target applications including high performance core material, energy absorption or packaging.

Flexural Behavior of Hybrid Composite Beams

This paper presents the development of composite beams, which consist of hybrid carbon and glass fiber-reinforced polymer (FRP) I-beams and precast, ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs. Hybrid FRPs (HFRPs) provide the advantage of high resistance to corrosion, while UHPFRC has great strength and durability. The combination of these two materials is expected to benefit structures subjected to severe environmental conditions and to respond to the need for accelerated bridge construction. Three full-scale composite beams with varied UHPFRC slab width were tested under four-point flexural loading. Bolt shear connectors with and without epoxy bonding were used in the tested beams. The bolt shear connectors and epoxy were used to resist the horizontal shear flow at the interface between the HFRP I-beam and the UHPFRC slab. The composite action between the HFRP I-beam and UHPFRC slab was investigated. The test results showed that all of the composite beams exhibited significant improvements in stiffness and strength properties, above those of single HFRP I-beams without a UHPFRC slab. A fiber model was developed to predict the strength and stiffness of the composite beam, and the model accuracy was verified. Good agreement was found between the experimental and analytical results. The high tensile strength of a carbon FRP in an HFRP tensile flange could be used effectively, and the delamination failure of an HFRP compressive flange could be prevented through the addition of a UHPFRC slab on the top flange of the HFRP I-beam. The study revealed that HFRP–UHPFRC beams were efficient and could provide a competitive, cost-effective, and sustainable solution to bridge structures.

Comparing the effect of Glucosamine and Glucosamine With Alendronate in Symptomatic Relieve of Degenerative Knee Joint Disease: A Double- blind Randomized Clinical Trial Study

Background:: Degenerative Joint Disease (DJD) is the most common joint disease in human beings. Previous studies have explained that glucosamine is preferred as placebo and in efficacy compared with NSAID’s in treatment of patients’ knee osteoarthritis. Alendronate was used to treat osteoporotic patients and its efficacy was established. Objectives:: The aim of this study was to compare the efficacy of administration of glucosamine alone and its combination with alendronate in osteoarthritis of the knee. Patients and Methods:: The study included 130 patients with osteoarthritis who randomly received glucosamine alone (group II) (500mg TDS), or combination of glucosamine (500mg TDS) and alendronate (70mg weekly) (group I) for 12 weeks. Patients were evaluated on 1, 3, 6 and 12 weeks after beginning the treatment to evaluate efficacy of each treatment. Results:: Statistically, there was no significant difference in pain index (P > 0.05) but in the two groups the mean of pain index decreased in a similar fashion. The stiffness index in combination treatment group (group I) decreased more than glucosamine group (group II) (P < 0.05). The function of joints in combination treatment group (group I) improved after 12weeks. The bone mineral density (BMD) at 12weeks in combination therapy group improved. Conclusions:: Combination therapy of glucosamine and alendronate indicated significant improvement of stiffness, function, BMD of osteoarthritis compared with glucosamine alone but there was no statistically significant decrease in pain index. It can be concluded that the combination of glucosamine and alendronate provide better and more rapid improvement in patients with osteoarthritis.

Comparing the effect of Glucosamine and Glucosamine With Alendronate in Symptomatic Relieve of Degenerative Knee Joint Disease: A Double- blind Randomized Clinical Trial Study

Degenerative Joint Disease (DJD) is the most common joint disease in human beings. Previous studies have explained that glucosamine is preferred as placebo and in efficacy compared with NSAID's in treatment of patients' knee osteoarthritis. Alendronate was used to treat osteoporotic patients and its efficacy was established. The aim of this study was to compare the efficacy of administration of glucosamine alone and its combination with alendronate in osteoarthritis of the knee. The study included 130 patients with osteoarthritis who randomly received glucosamine alone (group II) (500mg TDS), or combination of glucosamine (500mg TDS) and alendronate (70mg weekly) (group I) for 12 weeks. Patients were evaluated on 1, 3, 6 and 12 weeks after beginning the treatment to evaluate efficacy of each treatment. Statistically, there was no significant difference in pain index (P > 0.05) but in the two groups the mean of pain index decreased in a similar fashion. The stiffness index in combination treatment group (group I) decreased more than glucosamine group (group II) (P < 0.05). The function of joints in combination treatment group (group I) improved after 12weeks. The bone mineral density (BMD) at 12weeks in combination therapy group improved. Combination therapy of glucosamine and alendronate indicated significant improvement of stiffness, function, BMD of osteoarthritis compared with glucosamine alone but there was no statistically significant decrease in pain index. It can be concluded that the combination of glucosamine and alendronate provide better and more rapid improvement in patients with osteoarthritis.

Efficacy of pregabalin in a case of stiff-person syndrome: Clinical and neurophysiological evidence

Symptomatic treatment of stiff-person syndrome (SPS) might be challenging and a significant improvement of stiffness and rigidity is generally reached with high doses of benzodiazepines or baclofen causing side effects.A 71-year old woman diagnosed with SPS complained of marked stiffness of trunk and lower limb muscles with sudden painful spasms. She was unable to walk and she could not lean on her right leg. Cortical silent period (CSP) duration evaluated from right abductor pollicis brevis (APB) with transcranial magnetic stimulation was shortened. Polygraphic electromyographic (EMG) evaluation from paraspinal and leg muscles disclosed continuous motor unit activity at rest with interference muscular pattern. Symptomatic treatment with diazepam was withdrawn because of excessive sedation. In order to relieve the intense lumbar pain, she was prescribed pregabalin; since the day after, rigidity and painful spasms dramatically improved and she could walk without assistance. The clinical benefit persisted at 3months follow-up and was paralleled by almost complete disappearance of EMG activity at rest and prolongation of CSP. The clinical and electrophysiological data in this SPS patient suggest the possible efficacy of pregabalin as symptomatic treatment without any significant side effects, which needs to be replicated in larger case series.

A Technique for Stiffness Improvement by Optimization of Fiber Steering in Composite Plates

A methodology for stiffness improvement by optimal orientation of fibers placed using fiber steering techniques of composite plates has been developed and is described here. A genetic algorithm is employed to determine the optimal orientation of the tow fibers and, in addition, once the plate has been divided up into cells in order to apply the technique, the orientation gradient between adjacent cells is capped. The finite element method (FEM) is used to determine the fitness of each design candidate. The approach developed also differs from existing ones by having a more sophisticated chromosome string. By relying on the algorithm for the calculation of the fiber orientation in a specific cell, a relatively short and rapid convergence string is assembled. The numerical results obtained show a significant improvement in stiffness when the fiber orientation angle is allowed to vary spatially throughout the ply.

A New Method to Improve the High‐Temperature Mechanical Properties of Ti3SiC2by Substituting Ti with Zr, Hf, or Nb

Ti3SiC2shows a unique combination of the properties of both metals and ceramics. However, its stiffness and strength lose rapidly above 1050°C, which is the main obstacle for the high‐temperature application of this material. To improve the high‐temperature mechanical properties of Ti3SiC2, Zr, Hf, or Nb were used as dopants in Ti3(SiAl)C2. At room temperature, the Zr‐, Hf‐, or Nb‐doped Ti3(SiAl)C2ceramics have comparable stiffness, hardness, strength, and fracture toughness with those of Ti3(SiAl)C2. At high temperatures, however, a significant improvement in stiffness and strength has been achieved for (Ti1−xTx)3(SiAl)C2(T=Zr, Hf, or Nb). (Ti1−xTx)3(SiAl)C2can retain high degrees of stiffness and strength up to 1200°C, which is 150°C higher than those for Ti3(SiAl)C2.

Fat graft migration causing recurrent cervical cord compression.

Fat graft migration following spinal cord surgery is an uncommon problem. Only few cases of fat graft migration causing cauda equine syndrome, recurrent sciatica, and root compression following lumbar spine surgery have been reported. We report a case of fat graft migration causing symptomatic cervical cord compression. A 45-years-old male with cervical spondylosis underwent anterior C4-5 discectomy and excision of hypertrophied ligament. A dural tear that occurred during the procedure was repaired with fat graft harvested from thigh. Significant improvement in stiffness was noted postoperatively. After 15 days, the patient presented again with worsening lower limbs stiffness. Magnetic resonance imaging of spine was done which revealed displacement of the fat graft causing cervical cord compression. Re-exploration was done and the migrated fat graft was removed. Post operatively patient noticed significant improvement in stiffness in both lower limbs. Autologous fat graft is one of the best materials used in sealing the dural cerebrospinal fluid leak during spinal surgery. However sometimes it may migrate and cause compression of cord and roots with relative symptoms. This complication should be kept in mind as removal of migrated fat graft will relieve these symptoms.

Assessment of efficacy and safety of “Chondroxid” gel in comparison with “Finalgel" in patients with knee osteoarthritis

Objective. To assess efficacy, safety and aftereffect duration of 6-week local therapy of “Chondroxid” gel in comparison with ‘‘Finalgel” in patients with knee osteoarthritis. Material and methods. 60 outpatients (2 groups 30 pts in each) mainly women (59 pts) with knee osteoarthritis (II-III stage according to Kellgren-Lawrence) fulfilling ACR criteria aged 45 to 70 years (mean age 57,3±6,3 years) with pain at walking 40 mm and more on visual analog scale (VAS), Lequesne index from 4 to 10 regularly receiving NSAIDs for 30 days during previous 3 months were included. Follow up duration was 8 weeks (6 weeks - treatment and 2 weeks follow up to assess drug effect).The pts used gels “Chondroxid”and “Finalgel” 3 times a day 9-11 cm of drug extruded at fully open tube orifice (3-4 g). Efficacy assessment was performed with common criteria: WOMAC index (assessment of pain, stiffness and functional disability), summated functional Lequesne index, walking speed (15 m), treatment efficacy assessment by doctor and pt (improvement, absence of response, deterioration), daily requirement in NSAIDs, knee joint sonographic examination data. Results. Definite analgesic effect was achieved with both drugs. “Chondroxid” gel provided faster improvement: pain significantly decreased already after a week of treatment (p=0,05). Significant improvement of stiffness, joint function and walking speed was achieved after 2 weeks of treatment and was maintained till the end of treatment in both groups (p=0,05). Summated WOMAC index changed in accordance with pain. Severity Lequesne index significantly decreased in both groups but provided more prominent improvement (p<0,015). Significant improvement of function and summated WOMAC index was revealed in the main group pts at the second visit (after 1 week of treatment) what confirmes fast effect of “Chondroxid” gel. Later effect in both groups was similar. In 2 weeks after the end of treatment aftereffect was maintained in both groups but in the main group decrease of pain was more prominent (100,2±58,6 mm vs 130,8±59,6 mm in control, p<0,05). Local adverse events appeared in 4 pts only during treatment with “Chondroxid” gel: in 3 pts — knee periarticular edema and in 1 pt the drug was withdrawn due to skin itch and hyperemia at the site of gel application. Conclusion. The results of the study showed that “Chondroxid” gel effect on pain and joint function in knee osteoarthritis is comparable with “Finalgel”, but “Chondroxid” gel acts faster and its aftereffect lasts longer than that of “Finalgel”.

A novel fiber treatment applied to woven jute fabric/vinylester laminates

In this work, a novel fiber treatment consisting on an alkali treatment superimposed to biaxial tensile stress was successfully applied to woven jute fabric/vinylester laminates. The effect of treatment on the composites tensile properties was investigated at two different times of treatment. A significant improvement in stiffness was achieved by the composite treated with alkali under stress for 4 h. However, no significant differences between the stiffness of the untreated composite and the composites treated with alkali under stress for 24 h were found. On the other hand, irrespectively of the time of treatment, the composites with fabrics treated with alkali under stress showed the highest values of tensile strength. From results of fabrics tensile tests, compression shear tests and X-ray diffraction analysis, the improved tensile properties exhibited by the composites with treated fabrics could be attributed to structural changes of the fibers as well as to a change in the fiber/matrix interfacial properties.

Experimental tests and numerical analysis of a real RC structure upgraded by means of C-FRP

The paper presents results of the analysis of the lateral-load response of an existing RC structure seismically upgraded by means of C-FRP. The structure was tested “as-is” under monotonic lateral loading conditions. It failed by a column-type collapse mechanism. The structure was repaired and upgraded by means of C-FRP. The structure has been tested again by a cyclic load test. Results demonstrate the successful implementation of C-FRP with a significant improvement of stiffness, strength and lateral displacement capacity of the upgraded structure. Finally a numerical study has been started with the aim to correctly capture the experimental results.