Excellent Load-carrying Capacity Research Articles

Performance of precast segmental concrete beams posttensioned with carbon fiber-reinforced polymer (CFRP) tendons

Precast segmental prestressed concrete beams (PSBs) have been widely used in many elevated highway bridge projects around the world. Steel tendons at joint locations, however, are vulnerable to corrosion damages, which cause deteriorations and in extreme cases lead to the collapse of the whole structures. This study experimentally investigates the use of carbon fibre-reinforced polymer (CFRP) tendons as an alternative solution for the PSBs to tackle the corrosion issue. Four large-scale segmental T-shaped concrete beams with internal bonded or unbonded tendons and dry or epoxied joints were built and tested under four-point loading. The test results indicated that CFRP tendons showed satisfactory performances therefore could replace steel tendons for the use in PSBs. All the tested beams exhibited excellent load-carrying capacity and ductility. Tendon bonding condition greatly affected the flexural performance of the segmental beams. Joint type had only a slight effect on the load-carrying capacity and ductility of the beams, but significantly affected the beams’ initial stiffness. Unbonded tendons experienced an evident reduction in the tendon strength at the ultimate stage as a consequence of the loading type, harping effect and joint opening. Both AASTHO-1999 and ACI 440.4R-04 predicted well the tendon stress, thus the load-carrying capacity of the beams with bonded tendons, however, the accuracy significantly reduced for the cases with unbonded tendons. Similarly, the codes did not well estimate the deformation capacity of the prestressed beams with unbonded tendons. An empirical formula is proposed to predict the deflections of beams with unbonded tendons, which yields very close predictions to the experimental results.

Friction and wear behaviors of MoS2-multi-walled-carbonnanotube hybrid reinforced polyurethane composite coating

MoS2-multi-walled-carbon-nanotube (MWCNT) hybrids containing two-dimensional MoS2 and one-dimensional MWCNTs were synthesized through a one-step hydrothermal reaction. X-ray-diffraction and transmission-electron-microscopy results demonstrated that MoS2 nanosheets were successfully synthesized, and uniformly anchored on the MWCNTs’ surfaces. Furthermore, the effects of the MoS2-MWCNT hybrids on the tribological performances of polyurethane composite coatings were investigated using a UMT-2MT tribo-tester. Friction and wear test results revealed that the friction coefficient and wear rate of a 3 wt% MoS2-MWCNT-1 filled polyurethane composite coating were reduced by 25.6% and 65.5%, respectively. The outstanding tribological performance of the MoS2-MWCNT-1 reinforced polyurethane composite coating was attributed to the excellent load-carrying capacity of the MWCNTs and good lubricant ability of MoS2. The surface morphologies of the worn surfaces and counterpart ball surfaces were investigated to reveal the wear mechanisms.

Experimental study on wheel-spoke crossed cable structures

Wheel-spoke crossed cable structure is a new type of cable-strut structure. In this article, the tension forming and static performance of wheel-spoke crossed cable structure are experimentally investigated by testing four scale models under full-span and half-span downward uniform load, and the effect of structural parameters including variable prestress level, height difference between inner ring and outer ring, and layer height of inner ring is studied by finite element method as well. The test results indicate that radial cables tensioning scheme is effective for wheel-spoke crossed cable structure to reach initial prestress state, and wheel-spoke crossed cable structure possesses excellent load-carrying capacity and structural stiffness since internal forces and vertical displacements of models vary almost linearly under such load cases. Moreover, the static test results are in good agreement with the finite element analysis results, confirming that the model design, measurement methods, and loading schemes are reasonable. Therefore, the results of this study can provide valuable reference for the design and application of wheel-spoke crossed cable structure.

The extreme pressure and lubricating behaviors of potassium borate nanoparticles as additive in PAO

ABSTRACTThe potassium borate nanoparticles (nPB) as lubricant additive were prepared with an eco-friendly method. The tribological properties of nPB and ZDDP as lubricant additives in polyalphaolefin (PAO) were systematically evaluated using a four-ball tribometer and a SRV fretting friction and wear tester, which suggested that nPB exhibited excellent extreme pressure capacity, and better anti-wear and friction-reducing properties than ZDDP. Results of surface analyses show that the good lubricating properties and excellent load-carrying capacity of nPB in PAO are ascribed to the boundary protecting films, which were composed of some easy-shearing compounds: B2O3, FexBy and Fe2O3.

Full-Scale Testing of Geosynthetic-Reinforced, Soil-Integrated Bridge System

This paper focuses on the preliminary results of static load tests that were conducted on a geosynthetic-reinforced, soil-integrated bridge system (GRS-IBS) in Louisiana. Sixteen loading tests that used two fully loaded trucks were conducted on the instrumented GRS-IBS bridge. The bridge was surcharge loaded to stress levels well in excess of working load conditions. To evaluate the performance of the GRS-IBS abutment under different load tests, various types of instrumentation were installed; these included shape accelerated arrays, pressure cells, strain gauges, piezometers, and thermocouples. The primary measurements were the horizontal deformations near the front wall, vertical deformation of the GRS abutment, distribution of stresses in the GRS abutments and below the reinforced soil foundation, and distribution of strains along the geosynthetic reinforcements. Measurements from the instrumentation provided information needed to verify design factors and parameters for the GRS-IBS abutment. The bridge settlement and lateral movement of the facing wall were within the serviceability level; this result demonstrated excellent load-carrying capacity of the GRS abutment. The locus of maximum strains in the abutment varied by the surcharge load and did not correspond to the (45 + ϕ/2) line, especially when the surcharge load was placed at the bridge. The results of the load test revealed that the GRS-IBS bridge responses to the load tests were well within the serviceability limits, and the overall performance of the GRS-IBS was within acceptable tolerance in terms of measured strains, stresses, settlements, and deformations.

Effect of Nitrogen Atoms Number and Spatial Location on Tribological Properties of Nucleobase Derivatives

Four kinds of ashless, non-phosphorus and non-sulfur oil-soluble compounds of nucleobase derivatives were evaluated as lubricant additives in poly(ethylene glycol) (PEG) for steel–steel contact under room temperature, and their electrochemical corrosion behaviors were measured by Tafel polarization. The morphologies and chemical features of the worn surfaces were investigated by scanning electron microscope and X-ray photoelectron spectroscopy (XPS). The results showed that the nucleobase derivatives as 2 wt% additive show excellent load-carrying capacity, friction-reducing and anti-wear performance. It is also found that the tribological performance of the two purine derivatives is better than that of the two pyridine derivatives. The corrosion behaviors of four PEGs with 2 wt% different nucleobase derivative additives on pure coppers exhibit much better than those of pure PEG. The XPS results indicated the excellent tribological properties are attributed to the formation of tribochemical adsorption and chemical reaction films on the worn surfaces, which may prevent the sliding surfaces from straight asperity contact and markedly improve friction-reducing and anti-wear behaviors.

Preparation of polyimide-graphite composite and evaluation of its friction behavior at elevated temperatures

Abstract In this paper, polyimide-graphite (PG) composite was prepared and used as a solid lubricant at elevated temperatures. PG composite was characterized by X-ray diffraction, and its thermal stability was evaluated based on thermogravimetric/differential thermal analysis and Fourier transform infrared spectrometry analysis. The results show that in PG composite, there was some interaction between the graphite (GR) and the polyimide (PI) matrix. Consequently, the PG composite exhibited better thermal stability than PI. The friction behavior of the PG composite sliding against steel at elevated temperatures (300–600°C at an interval of 100°C) was evaluated with a ring-on-ring tribometer. It was found that the PG composite exhibited excellent friction-reducing ability and good load-carrying capacity in the temperature range of 300–600°C and applied loads of 300–700 N. Moreover, this excellent lubricating performance of the PG composite might be attributed to its good thermal stability as a result of the interaction between the GR and the PI matrix. Therefore, PG composite could be used as an excellent solid lubricant under the high-temperature conditions.

Effect of Compatibility between AlN Nanoparticles and Borated Bis-Succinimide on Tribological Properties of Base Oil

The purpose of the research was to investigate effect of compatibility between AlN nanoparticles and borated bis-succinimide on tribological properties of base oil. The load-carrying capacity and anti-wear (AW) performance of base oil that contains aluminum nitride (AlN) nanoparticles or borated bis-succinimide (T152B) additive was examined; the tribological properties of the compatibility between AlN and T152B were also examined. The experimental results showed that AlN nanoparticles additive can effectively improve load-carrying capacity and anti-wear performance of base oil. AlN nanoparticles and T152B compatibility experiments showed that two additives have synergies to improve anti-wear performance of base oil. These findings indicate that AlN nanopaticles is an excellent load-carrying capacity and antiwear additive, and it can be used with T152B together in base oil.

Shape Determination and Static Experimental Study of Double Inner and Outer Latticed Shell String Structure

A new type of space structure called the double inner and outer latticed shell string structure, which can reduce the space occupied by the roof and be laid easily using a rigid roofing material, is proposed. Numerical algorithm for shape determination of this new space structure is introduced and some suggestions for improvement are put forward. One example is investigated and the results confirm the validity of the above method. Finally, a model experiment based on a practical engineering application is introduced. Experimental results are compared with those of the finite element numerical analysis and results show that the theoretical value and the experimental value match well, which reveals that the model design, loading scheme and measuring plan meets experimental requirements. The internal forces and the structure deformation vary linearly for full span load cases, which reveals that the double inner and outer latticed shell string structure has an excellent load-carrying capacity and structural rigidity, and has broad application prospects.

Fabrication and Tribological Study of Graphene Oxide/Multiply-Alkylated Cyclopentanes Multilayer Lubrication Films on Si Substrates

Multilayer films based on graphene oxide (GO) and multiply-alkylated cyclopentanes (MACs) have been fabricated successfully on silicon substrate via both self-assembled and dip-coating technologies. Given the excellent mechanical properties and frictional properties of GO, the resulting multilayer films composed of GO and MACs with excellent lubricating property are expected to possess improved comprehensive tribological performances. In the current paper, the surface morphology and chemical composition of the films were analyzed using water contact angle meter, X-ray photoelectron spectroscope, and atomic force microscope. A ball-on-plate tribometer was used to evaluate the tribological performances of the films. The results showed that the new multilayer films exhibited excellent load-carrying capacity and durability. Therefore, they are hoped to find promising applications in the lubrication of microelectromechanical systems.

Hydrothermal Synthesis of Copper Zirconium Phosphate Hydrate [Cu(OH)2Zr(HPO4)2·2H2O] and an Investigation of its Lubrication Properties in Grease

Copper zirconium phosphate hydrate (Cu(OH)2Zr(HPO4)2·2H2O, hereafter referred to as Cu-α-ZrP) with high crystallinity was directly synthesized in a NaF-CuO-ZrO-P2O5-H2O system under hydrothermal conditions. The copper ion was confirmed to be an exchangeable cation in the Cu-α-ZrP through elemental analysis and a proton ion exchange process. The crystal structure of the Cu-α-ZrP was determined ab initio by using X-ray powder diffraction data. In the structure, the CuO6 octahedron would be located in an exchangeable atom position. Moreover, Cu-α-ZrP was evaluated as an additive in grease in a four ball test. The maximum nonseizure load (PB, representing the load-carrying capacity) of the base grease containing Cu-α-ZrP was increased from 353 to 1235 N. The excellent load-carrying capacity may be explained by the easier adherence of the material to the worn surface forming a tight protective film.

Importance of adaptive multimode lubrication mechanism in natural and artificial joints

The healthy natural synovial joints maintain excellent load-carrying capacity and lubricating properties with extremely low friction and minimum wear even under heavily loaded conditions. The superior lubricating performance appears to be actualized by not single lubrication mode but the synergistic combination of various modes depending on the severity of operating conditions. This mechanism is called adaptive multimode lubrication and the application of this good working lubrication mechanism to artificial joints with soft layer is expected to contribute to remarkable improvement in longevity of joint prostheses. However, some of detailed mechanisms in natural synovial joints have not yet been clarified. In this article, the effectiveness of biphasic lubrication in natural synovial joints was examined by biphasic finite element analysis under both the on–off loading (migrating contact) and the continuous loading (continuous contact) to cartilage. Then, the method to suppress the gradual rising in friction for articular cartilage under the continuous loading is discussed. Finally, the effectiveness of fibre reinforcement in hydrogel artificial cartilage was examined in walking simulator test.

Comparing tribological behaviors of sulfur- and phosphorus-free organomolybdenum additive with ZDDP and MoDTC

A new kind of sulfur- and phosphorus-free organomolybdenum oil-based additive N, N-bis (2-hydroxyethyl)-dodecanamide molybdate (NNDM) was prepared. Its tribological performances as additive in base oil 150SN were examined on a four-ball tester, and compared with those of ZDDP and MoDTC under boundary lubrication condition. The tribofilm NNDM generated on the worn surface was analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results showed that NNDM blend oil exhibited excellent load-carrying capacity, significantly reduced friction coefficient and wear rate of worn surface, which could be attributed to high amount of long-chain alkylamide and MoOx in NNDM tribofilm.

Tribological Property of a Triazine Derivative in Rapeseed Oil

2-propylamino-4,6-(O,O’-dibuthyldithiophosphate)-s-1,3,5-triazine(DPOB)was synthesized and it’s tribological behavior as lubricant in rapeseed oil (RSO) were evaluated using a four-ball tester. The lubrication mechanism was investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results indicate that the compound possess excellent load-carrying capacity and antiwear ability, and has some friction-reducing property only under the low load condition. Based on the results of XPS and SEM analysis, it can be seen that tribochemical reaction occurred between the synthesized compounds and metal surfaces during the sliding process, to form a complex film which has excellent load-carrying capacity and antiwear ability.

Tribological study of novel S–N style 1,3,4-thiadiazole-2-thione derivatives in rapeseed oil

Two non-phosphorus and ashless 1,3,4-thiadiazole-2-thione derivatives, 5-dodecyldithio-3-phenly-1,3,4-thiadiazole-2-thione (DPTT) and 5-cetyldithio-3-phenyl-1,3,4-thiadiazole-2-thione (DHTT), were synthesized and their tribological behaviors as additives in rapeseed oil (RSO) were evaluated using a four-ball friction and wear tester. Their thermal stabilities and anticorrosive properties were investigated. The results indicate that the additives possess good thermal stabilities, corrosion inhibiting abilities and excellent load-carrying capacities. Moreover, they both have good anti-wear and friction-reducing property at relatively low concentration and under all test loads. The worn surfaces of the steel balls were observed using a scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is supposed that the synthetic additives adsorb and react with the steel surfaces during the rubbing process and generate a surface protective film composed of sulfate, sulfide, iron oxide and organic nitrogen-containing compounds, which accounts for the better tribological behaviors of the base stock containing the synthetic additives as compared with the base stock alone.

Tribological performance and chemistry of films for di-n-butyl dithiocarbamate derivatives in rapeseed oil

Two di-n-butyl dithiocarbamate derivatives were easily synthesized. Their tribological performances as lubricating oil additives in rapeseed oil were evaluated using a four-ball machine, and their chemistry of films was analyzed with X-ray absorption near-edge spectroscopy (XANES). The results indicate that the two compounds possess excellent anti-wear property and good load-carrying capacity. According to the XANES results, for the thermal films, the outer surfaces are mainly composed of N, S-containing polymer and ferric sulfate, and the near-surface and the bulk are composed of ferrous sulfate, while for the anti-wear films, the outer surfaces are only composed of ferric sulfate, but the near-surface and the bulk are mainly composed of ferrous sulfate.

Tribological behavior of three novel triazine derivatives as additives in rapeseed oil

Three novel phosphorus-free triazine derivatives, referred to as ZOO, ZOS and ZDION, respectively, were synthesized. Their thermal stabilities and anticorrosive properties were investigated. Their tribological behaviors as additives in rapeseed oil were evaluated using four-ball friction and wear testers as well. The results suggest that all the synthesized compounds have good thermal stability, corrosion inhibiting ability and excellent tribological behavior. That is, ZOS has the best extreme pressure, antiwear and friction-reducing properties under a wide range of test conditions. And, ZOO generally possesses excellent load-carrying capacity and good antiwear and friction-reducing abilities. However, ZDION shows poor antiwear effectiveness in rapeseed oil, though it is capable of improving the load-carrying capacity and friction-reducing ability of the base stock under high concentration (>1.5 wt.%) and low load (<392 N). The worn surfaces of the steel balls were observed using a scanning electron microscope coupled with an energy dispersive spectrometer (SEM/EDS) and X-ray photoelectron spectroscope (XPS). It is supposed that the synthetic additives adsorb and react with the steel surfaces during the rubbing process and generate a surface protective film composed of sulfate, sulfide, iron oxide and N- and/or O-containing organic compounds, which accounts for the better tribological behaviors of the base stock containing the synthetic additives as compared with the base stock alone.

The Tribological Performance of S-[2-(Acetamido) Benzothiazol-1-yl] N,N-Dioctyl Dithiocarbamate as an Additive in Rapeseed Oil

A new derivative of benzothiazol, S-[2-(acetamido) benzothiazol-1-yl] N,N-dioctyl dithiocarbamate, was synthesized. The tribological behavior of the synthesized compound as an additive in rapeseed oil was evaluated using a four-ball friction and wear tester, and compared with that of zinc butyloctyl dithiophosphate (ZDDP) and zinc dibutyl dithiocarbamate (ZDTC). The morphologies and elemental chemical states on the worn surfaces of the lubricated GCr15 steel were investigated by means of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The biodegradability (fate) and microbial toxicity (effects) measurement of the additive were also performed. The results indicate that the compound possesses excellent load-carrying capacity, antiwear and friction-reducing properties as compared with rapeseed oil alone. The antiwear and friction reduction properties of the novel compound are similar to those of ZDDP and ZDTC; and its load-carrying capacity is similar to ZDTC, but is better than ZDDP. The excellent tribological behavior of the novel compound is attributed to chemical adsorption on and tribochemical reaction with the steel surface, with the generation of a surface protective film composed of FeS, FeSO4, etc. Measurements of biodegradability and microbial toxicity show that the additive has high biodegradability, and microbial toxicity needed to be further lowered.

Study of the tribological behaviors of S, P-containing triazine derivatives as additives in rapeseed oil

A series of S, P-containing triazine derivatives, 2,4-bis-(diethylamino)-6-( O, O′-dialkyl dithiophosphate)- s-1,3,5-triazine, which are potential environmentally friendly lubricating oil additives, were synthesized. The tribological properties as lubricating oil additives in vegetable oil were evaluated using a four-ball tester. The results show that the series of triazine derivatives possess good antiwear performance, excellent load-carrying capacity. These compounds also show good friction-reducing properties. The action mechanism was estimated through analysis of the worn surface with X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM).

The tribological behaviour of some triazine–dithiocarbamate derivatives as additives in vegetable oil

Three novel ashless triazine–dithiocarbamate derivatives, which are potential environmentally friendly oil additives, were synthesized. Their tribological properties as additives in rapeseed oil (RSO) were evaluated using a four-ball tester. Their anticorrosive properties and thermal stabilities were also investigated. The results indicate that the three novel triazine–dithiocarbamate compounds possess excellent load-carrying capacity, good corrosion inhibiting performance and high thermal stability. Although these additives show friction-reducing property at high additive concentration (5 wt.%), they have friction increase and wear promote natures in most cases. The elemental composition and chemical state of the antiwear films generated on steel counterface were investigated with scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS). It was found that the synthetic additives reacted with the counterface metal and generated a surface protective film consisting of sulfate, FeS and absorbed compounds containing organic-N.