Rupture Strength Research Articles

Mechanical Performance Assessment of Physician Modified Aortic Stent Graft

This study aimed to compare various fenestration configurations of physician modified aortic stent grafts in order to identify which design parameters have a significant influence on the mechanical behaviour of the fenestration. the fenestration configurations were considered according to different manufacturing parameters: cutting technique, fenestration reinforcement, suture material, reinforcement loop design, and number of suture points. The performance of the graft/bridging stent assembly was assessed at various levels: (1) branch pull out force; (2) fenestration enlargement and rupture strength; (3) balloon angioplasty resistance; and (4) behaviour under cyclic fatigue. Sixty manual fenestrations were created. The tests performed on the fenestrations had several main findings. First, reinforcement increased the radial force on the branch, which increased the pull out force; this may limit migration of the bridging stent invivo. The phenomenon was amplified with a snare reinforced fenestration, which seemed to be the most efficient. Moreover, increasing the number of suture passes also appeared to increase the branch extraction force securing the assembly. The enlargement tests showed that non-reinforced fenestrations had the weakest radial strength. This was confirmed with the balloon angioplasty test, which showed that these latter specimens undergo the most significant textile degradation. After fatigue tests, all fenestrations were larger, showing that elastic recoil was incomplete in all samples. The largest recoil was observed in the non-reinforced ophthalmological cautery (OC) fenestrations (40%). Regarding the behaviour of the samples up to rupture, all samples behaved in a similar way; however, the double loop fenestration strength level was the highest. This study demonstrated that the snare double loop reinforcement has an advantage regarding durability of the graft branch assembly. Moreover, non-reinforced fenestrations show signs of weakness and lack of stability, which questions the in situ or laser fenestration procedures.

On the dissolution and enhancement mechanisms of Cr doping in Mo2FeB2-based cermets

In this work, the effect of Cr doping on the mechanical properties of Mo2FeB2-based cermets was studied. The results indicated that the hardness was continuously enhanced with the Cr contents, while the transverse rupture strength increased and then decreased. With the increase of Cr contents, the decreased binder deteriorated the fracture toughness. In the Mo2FeB2 particles of the cermets, Cr atoms mainly substituted the large-size Mo atoms instead of Fe. However, the first-principles calculation results showed that when the Cr atoms occupied the sites of Fe, the Cr-doped Mo2FeB2 were more thermodynamically stable. Based on the elemental composition of Cr-doped Mo2FeB2 bulks, the sites of Cr in Mo2FeB2 were mainly determined by the contents of Mo and Fe. In the Mo-depleted Mo2FeB2 bulk, Cr atoms preferred to substitute the Mo atoms, while Cr atoms occupied the sites of Fe in the Fe-depleted Mo2FeB2 bulk. Hence, the relatively lower content of Mo in Mo2FeB2-based cermets resulted in the substitution of Mo with Cr atoms. The intrinsic hardening of Mo2FeB2 induced by Cr doping contributed to the enhanced hardness of Mo2FeB2-based cermets. Besides, the decreased bulk modulus and shear modulus were conducive to the improvement of the transverse rupture strength.

Experimental study of the torsional effect for yarn break load test of polymeric multifilaments

Polymeric multifilaments have gained a significant interest in recent decades. In the studies of mechanical characteristics, although there are different types of tests, such as rupture, abrasion, creep, impact and fatigue, it can be said that the main mechanical characterisation is the tensile rupture strength (Yarn Break Load, YBL), which also serves as a parameter for other tests. The objective of this work is to evaluate the results of breaking strength under different torsional conditions in polymeric multifilaments and to determine optimal twists for failures. The test were carried out with the following materials: polyamide, polyester, and high modulus polyethylene (HMPE), and for torsional conditions: 0, 20, 40, 60, 120, 240, and 480 turns per metre. As a result, for these torsion groups, curves were obtained for the three materials that present an optimal point of maximum rupture value, which was also experimentally proven. The twist that optimises the breaking strength of HMPE is 38 turns per metre, 56 turns per metre for polyester, and 95 turns per metre for polyamide. The twist groups that exceed the optimal torsion have a deleterious effect on the material, where the multifilament ceases to be homogeneous and starts to create an excessive "spring effect". The results found differ from the recommendation of the standard that regulates the YBL test, and thus, a relationship is built between groups of optimal torsion and linear density that provides evidence that the increase in linear density causes the optimal torsion for rupture to also increase, while the standard places a condition of 30 turns per metre for linear densities greater than 2200 dtex, and 60 turns per metre for linear densities less than 2200 dtex. In addition to optimal torsion values, this conclusion is paramount, the test procedure makes a general recommendation that does not optimise the breaking strength.

Influence of the vacuum hot pressing process on the microstructure, mechanical properties, and material characteristics of CrCoNiTa3 alloys

This research fabricates CrCoNiTa3 alloys using the vacuum hot pressing process, where micron grade chromium (6 μm), cobalt (3 μm), nickel (3 μm) and tantalum (25 μm) powders are mixed by means of ball milling. The experiments utilize various hot pressing temperatures (1000, 1050, 1100, and 1150 °C) and hot pressing pressures (20, 35 and 50 MPa) to determine the optimal hot pressing parameters for CrCoNiTa3 alloys, while simultaneously investigating the differences in microstructures and material characteristics. The results show that the optimal hot pressing parameters of this alloy were 1100 °C at 20 MPa for 1 h. The sintering density was enhanced to 8.34 g cm−3, and the hardness and transverse rupture strength (TRS) reached 72.9 HRA and 2266.1 MPa, respectively. Meanwhile, the electrical conductivity was 1.46 × 103 S cm−1 and the polarization resistance was 1309.1 Ω cm2. Furthermore, the EBSD results confirm that the FCC solid solution and twin of the CrCoNiTa3 crystalline structure, and no preferred grain orientation was found.

Ultra-high-performance concrete: Impacts of steel fibre shape and content on flowability, compressive strength and modulus of rupture

The impact of three-shaped steel fibres (straight, hooked end, and corrugated) with varying steel fibre (SF) contents (0.75 %, 1.5 %, and 2.5 % by volume fraction) on the fresh and mechanical characteristics of ultra-high-performance concrete was investigated in this investigation. The characteristics concerned included flowability, compressive strength, and modulus of rupture. The findings showed that using deformed fibres and increasing the fibre volume could gradually reduce the flowability of ultra-high-performance concrete. It also had a substantial impact on the compressive strength and modulus of rupture of ultra-high-performance concrete. At 28-d, its compressive strength and modulus of rupture were greater than 155 and 37 MPa, respectively, with the introduction of 2.5 % straight SFs. Moreover, the compressive strength increased by 50 % and 65 % for concrete comprising 2.5 % hooked end fibre and corrugated fibre, respectively, when compared to concrete with the same volume of straight fibre.

Design and development of an environmentally controlled enclosure for a commercial 3D printer

PurposeThe purpose of this study is to design and develop an environmentally controlled enclosure for commercial three-dimensional (3D) printers.Design/methodology/approachComputational fluid dynamics (CFD) simulations and experimental testing investigated various designs for environmentally controlled enclosures. CFD simulations provided the necessary information to select the optimal and feasible design, whereas experimental testing validated the CFD simulation results. An environmentally controlled environment allowed test samples to be printed at several relative humidity (RH) settings (20% RH, 50% RH and 80% RH). The test samples were characterized at both the macro and micro scales. The macroscale characterization was conducted using the static tensile testing procedure, while the microscale polymer material properties were determined using atomic force microscopy.FindingsAn environmentally controlled enclosure was designed and built to produce airflow in the print region with an average RH uniformity of over 0.70. Three batches of ASTM D638 standard test samples were printed at 20% RH (low RH), 50% RH (mid RH) and 80% RH (high RH). Macroscale characterization showed that the samples printed at lower humidity had statistically significantly higher tangent modulus, ultimate tensile strength and rupture strength. atomic force microscopy studies have also verified these results at the microscale and nanoscale. These studies also showed that a high humidity environment interacts with melted polylactic acid, causing additional surface roughness that reduces the strength of 3D-printed parts.Originality/valueThere is a need for stronger and higher-quality 3D-printed parts in the additive manufacturing (AM) market. This study fulfills that need by designing and developing an environmentally controlled add-on enclosure for the AM market.

Characterization and application of active films based on commercial polysaccharides incorporating ZnONPs

In the face of the environmental problems caused by using food packaging composed of non-renewable sources, the aim of this study was producing a new antimicrobial film, biodegradable and with UV barrier based on commercial κ-carrageenan/starch polysaccharides loaded zinc oxide nanoparticles (ZnONPs) for the first time by casting method. Different formulations of κ-carrageenan/starch/ZnONPs were extensively characterized. The X-ray patterns displayed diffraction peaks characteristics of the crystallographic plane of ZnONPs. The formation of the material composite was confirmed by specific signals in the FTIR spectrums and endothermic peak shift after ZnONPs addition. The ZnONPs (1.5 and 2 %) produce a more resistant material. The analysis of SEM (cracks remotion of film surface), mechanical properties (higher elongation at rupture and tensile strength), and opacity (low transparency) confirm this. Still, ZnONPs at 2 % produce a hydrophobic surface, justified by lower moisture content, water solubility, and higher WCA. The ZnONPs promoted UV barrier and antimicrobial activity against Escherichia coli, Salmonella Typhimurium, and Staphylococcus aureus microorganisms. Thus, the new active material was applied as a coating on fresh strawberries and delayed the ripening of the fruit, extending its shelf life. Therefore, we produced, characterized, and applied an active material with potential application in fresh food packaging.

The relationship between color and mechanical properties of heat-treated wood predicted based on support vector machines model

Abstract Thermal modification or heat treatment can cause the loss of mechanical property of wood. In this study, Poplar (Populus tomentosa Carr.) and spruce (Picea obies Mast.) were heat treated at 180, 200, and 220 °C for 2–10 h. Changes of color (L*, a* and b*) and mechanical strength including modulus of elasticity (MOE), modulus of rupture (MOR) and shear strength after heat treatment were analyzed. Time-temperature superposition methods were used to quantify color and mechanical strength. The prediction models of MOR, MOE and shear strength were assessed with support vector regression model (SVR) based on color parameters. The trends of color change and mechanical strength after heat treatment were highly consistent. The values of apparent activation energy (E a ) calculated from color parameters (110.6–187.2 kJ/mol) were identical to those from mechanical strengths (103.2–219.2 kJ/mol). Color parameters were used as input variables, and the MOE, MOR, and shear strength were output parameters in the established SVR model. Gaussian radial basis function (RBF) was found to be a kernel function for SRV model. Optimal hyperparameters in SVR model were obtained using cross-validation and grid search. The determination coefficients for MOE, MOR, and shear strength were 0.903, 0.835, and 0.865, respectively for poplar. The high correlation suggested that wood mechanical strength can be predicted non-destructively through measuring color parameters after heat treatment.

Effect of V doping on the microstructure and mechanical properties of Mo2FeB2-based cermets and investigation on the enhancement mechanism

In this study, the effect of V doping on the microstructure and mechanical properties of Mo2FeB2-based cermets was explored. The doped V element was mainly dissolved in the Mo2FeB2 particles to substitute the Mo atom inside without generating a new phase. Doping V element increased the volume fraction of borides and the forming temperature of the liquid, thus resulting in the formation of micro pores in Mo2FeB2-based cermets. The appropriate V additions simultaneously enhanced the hardness and transverse rupture strength of Mo2FeB2-based cermets, while the excessive V additions generated negative influences. The nanoindentation results indicated that the intrinsic hardness and Young’s modulus of Mo2FeB2 particle were enhanced monotonously with the increasing V contents. However, the V-containing Mo2FeB2 particles exhibited more brittleness. The first-principles calculation results showed that the enhanced covalent bonds in Mo2FeB2 contributed to the increased hardness. Moreover, V doping decreased the structural stability of Mo2FeB2 by forming the anti-bond. Additionally, the variations of bulk modulus, shear modulus and Poisson’s ratio caused by the V doping were also discussed based on the calculation results.

Coarse cemented carbide produced via binder jetting 3D printing

Until recently, cemented carbide produced via Binder Jetting 3D Printing (BJ3DP) resulted in microstructures with mixed WC grain size. Those materials exhibit excellent hardness and wear resistance but have transverse rupture strength that is lower than the strength of cemented carbide with a uniform grain size. The present investigation details the development of BJ3DP coarse tungsten carbide (WC-12%Co and WC-10%Co) that displays a sintered microstructure with uniform WC grain size. The free flowable (Carney flow <12 s/200 g) spherical powders exhibit very good printability and can be sintered to full density under standard sinter-HIP conditions (temperature 1460 °C, pressure 50 bar). The sintered mechanical properties compare well against cemented carbides produced by powder metallurgy. Vickers hardness, transverse rupture strength, and fracture toughness (determined by the Palmquist method) are in the range HV30 1050–1119, 2231–2684 MPa, and 18.8–19.4 MPa·m1/2, respectively. The wear properties were evaluated under abrasion and erosion using the ASTM B611 and ASTM G65 standard testing procedures. The wear resistance of the coarse BJ3DP cemented carbides compares well against conventionally produced cemented carbide. Parts over a wide range of sizes (from <1 g to 9 kg) and geometric complexities have been successfully printed and sintered with the new materials.

On the reaction mechanism of Mo2FeB2-based cermets and wear transition induced by self-lubricating tribo-oxide layer

During the sintering process, the phase evolution of Mo2FeB2-based cermets mainly occurred in the solid stage. When the liquid formed, the phase composition remained constant and the “dissolution-reprecipitation” process predominated the microstructural evolution. At 1250 °C, the hardness, transverse rupture strength and fracture toughness of Mo2FeB2-based cermets reached 88.6 HRA, 1480 MPa and 14.1 MPa⋅m1/2, respectively. The tribology and wear behaviors of Mo2FeB2-based cermets were evaluated from 25 °C to 800 °C. The abrasive wear prevailed at 25 °C, while the wear mechanism transitioned to oxidative mild wear due to the formation of the tribo-oxide layer at 400 °C and 600 °C. Besides the anti-wear Fe2O3, the lubricant MoO3 and B2O3 were also formed. The multi-component self-lubricating tribo-oxide layer simultaneously reduced the wear rate and coefficient of friction of Mo2FeB2-based cermets. However, by further increasing the temperature to 800 °C, the cracked matrix and impaired tribo-oxide layer resulted in the transition of wear mechanism to oxidative severe wear. The appropriate combination of load and temperature was necessary for the formation and stability of the tribo-oxide layer.

Optimization of mixture parameter for physical and mechanical properties of reactive powder concrete under external sulfate attack using Taguchi method

• Taguchi analysis has been used to determine optimum mix design parapeter of RPC exposed to different Na 2 SO 4 solutions and exposure conditions. • Optimized level for RPC mixture with different water to binder ratio, steel fiber contents, and silica fume contents depends on different external sulfate attack exposure conditions. • RPC appears to be sustainable and durable material under different external sulfate attack exposure conditions. Reactive powder concrete (RPC) is defined as a cementitious composite material with an optimized size of granular constituents, very low water-to-binder ratio (w/b), pozzolanic materials like silica fume (SF), and discontinuous fiber reinforcement. RPC applications include bridge decks and girders, seismic columns, wind turbine towers, and pile foundations. Especially, a durable and robust RPC pile foundation with long service life is essential in building construction because continuous maintenance is impossible. Moreover, natural in-situ conditions such as water table, temperature, and sulfate concentration in soil to which the pile foundation is exposed are critical and related to deteriorating the pile foundation. Therefore, the Taguchi design of experiments (DOE) was used in this research to determine the optimal RPC mixture with beneficial characteristics against external sulfate attack (ESA). Mixture design parameters included steel fiber content (0, 1 and 2 %), w/b (0.16, 20 and 0.24), and SF content (15, 20 and 25 %). In contrast, environmental conditions of ESA exposure contained three different sodium sulfate (Na 2 SO 4 ) concentrations (0.35, 1.05, and 3.15 M), cyclic and continuous exposure at normal temperature (20 °C), and continuous exposure at elevated temperatures (40 °C and 60 °C). The analytical and statistical investigation evaluated mass change, compressive strength, and modulus of rupture in RPC mixtures exposed to these conditions for 52 weeks. Test results show that cyclic exposure and increased solution temperature in ESA facilitate RPC damage. If measured after air drying, RPC mixtures subjected to cyclic ESA are especially susceptible to failure. Taguchi analysis indicated the optimum parameters’ level for mass change as: 0 % steel fiber, w/b = 0.16, and 20 % SF content; for the compressive strength: 2 % steel fiber, w/b = 0.24, and 20 % SF content; and, for modulus of rupture: 2 % steel fiber, w/b = 0.20, and 25 % SF content. In conclusion, RPC appears to be sustainable and durable material under different ESA exposure conditions.

Effect of Mo Content on In-Situ Anisometric Grains Growth and Mechanical Properties of Mo2FeB2-Based Cermets.

Mo2FeB2-based cermets have wide applications in fields of wear resistance, corrosion resistance and heat resistance due to their simple preparation process, low-cost raw materials, and prominent mechanical properties. Herein, Mo2FeB2-based cermets with xMo (x = 43.5, 45.5, 47.5, 49.5, wt.%) were prepared by means of the vacuum liquid phase sintering technique. Investigations on the microstructure and mechanical properties of Mo2FeB2-based cermets with Mo addition were performed. Experimental results show that, with Mo content increasing, the average particle size decreases gradually, revealing that the grain coarsening of Mo2FeB2-based cermets is controlled by interface reaction. In addition, Mo2FeB2 grains gradually transform from an elongated shape to a nearly equiaxed shape. The improvement of Mo2FeB2 hard phase on the morphology is mainly due to the inhibition of solution–precipitation reaction by increasing Mo. Furthermore, the relative density of cermets decreases due to the reduced Fe content. When Mo content is 47.5 wt.%, a relatively small grain size of Mo2FeB2 is obtained (about 2.03 μm). Moreover, with the increase in Mo content, hardness and transverse rupture strength (TRS) of Mo2FeB2-based cermets increase firstly and then decrease. Whereas, with increasing Mo content, the fracture toughness deteriorates gradually. When Mo content is 47.5 wt.%, the comprehensive mechanical properties of cermets are the best. The optimal raw material ratio for the preparation of Mo2FeB2-based cermets in this study is determined to be 47.5 wt.% Mo–6.0 wt.% B-Fe.

Effect of microporous aggregates and spinel powder on fracture behavior of magnesia-based refractories

The influences of microporous aggregates and spinel powder on the properties and fracture behavior of magnesia-based refractories were investigated by the three-point bending test and wedge splitting test with the digital image correlation method. With microporous aggregates instead of dense ones, lower thermal conductivity, higher cold modulus of rupture and compressive strength were observed for lightweight magnesia-based refractories. Besides, the results indicate that the strengthened interlocking interface between microporous aggregates and matrix in lightweight magnesia refractories decreased the proportion of crack propagation along the aggregate/matrix interface (PAM). This reduced the tortuosity of crack propagation as well as increased the brittleness. With the addition of spinel powder in the matrix, the pregenerated microcracks by thermal mismatch increased the PAM, which increased the tortuosity of crack propagation, improved fracture energy and reduced the brittleness. Lightweight magnesia spinel refractories merely showed a slightly higher brittleness than dense ones.

A thermochemical database from high-throughput first-principles calculations and its application to analyzing phase evolution in AM-fabricated IN718

A comprehensive thermochemical database is constructed based on high–throughput first-principles phonon calculations of over 3000 atomic structures in limited concentrations in Ni, Fe, and Co alloys involving a total of 26 elements including Al, B, C, Cr, Cu, Hf, La, Mn, Mo, N, Nb, O, P, Re, Ru, S, Si, Ta, Ti, V, W, Y, and Zr, providing thermochemical data largely unavailable from existing experiments. The database can be employed to predict the equilibrium phase compositions and fractions directly from first-principles by minimizing the chemical potential of a multicomponent system with a fixed overall chemical composition and a fixed temperature. It is applied to the additively manufactured nickel-based IN718 superalloy to analyze the phase evolution with temperature. IN718 is known for its great performance in tensile, fatigue, creep, and rupture strength, combined with easy fabrication and corrosion resistance. In particular, we successfully predicted the formation of L10-FeNi, γ’-Ni3(Fe,Al), α-Cr, δ-Ni3(Nb,Mo), γ”-Ni3Nb, and η-Ni3Ti at low temperatures (below 680 K), γ’-Ni3Al, δ-Ni3Nb, γ”-Ni3Nb, α-Cr, and γ-Ni(Fe,Cr,Mo) at intermediate temperatures (between 680 and 1140 K), and δ-Ni3Nb and γ-Ni(Fe,Cr,Mo) at high temperatures (above 1140 K) in IN718. These predictions are validated by EDS mapping of compositional distributions and corresponding identifications of phase distributions. The database is expected to be a valuable source for future thermodynamic analysis and microstructure prediction of alloys involving the 26 elements.

The Effect of an Additional Core Suture During Pulvertaft Tendon Repair: A Fresh-Frozen Cadaver Study

Pulvertaft tendon repair is a strong suture technique; however, proper tendon tension is impaired by repair site elongation. Therefore, methods to reduce postoperative elongation are warranted. This study aimed to determine the effects of additional core sutures during Pulvertaft tendon repair on repair site elongation and rupture strength. A total of 48 finger extensor tendons were harvested from fresh-frozen cadavers, and tendons with similar diameters were paired. The 24 pairs of tendons were divided into the following 4 groups: group I, 3 interlaced weaves only; group II, 3 interlaced weaves and 2 core suture strands with 4-0 nylon; group III, 3 interlaced weaves and 2 core suture strands with 4-0 FiberWire; and group IV, 4 interlaced weaves only. Each sutured tendon was placed in a Universal Testing Machine, and repair site elongation after repeated traction loads and rupture strength were measured. The mean elongation values were 2.74 ± 0.84 mm, 1.80 ± 0.16 mm, 1.60 ± 0.18 mm, and 1.92 ± 0.18 mm for groups I, II, III, and IV, respectively. The elongation values were significantly lower in groups II, III, and IV than in group I. The mean rupture strengths were 64.9 ± 16.0 N, 94.8 ± 17.2 N, 110.9 ± 21.3 N, and 104.9 ± 17.5 N for groups I, II, III, and IV, respectively. Rupture strengths were significantly higher for groups III and IV than for group I. After adding core sutures during Pulvertaft tendon repair, the elongation amount decreased, and the rupture strength improved. The study showed the effect of additional core sutures during Pulvertaft tendon repair, suggesting that it could be useful in reducing postoperative tendon elongation when extensor tendon transfers are performed.

Compressive strength, flexural strength and modulus of elasticity relationships of ternary blended concrete.

The paper presents the correlation between flexural strength and modulus of elasticity with respect to the compressive strength of ternary concrete (TC), made by incorporating the Micro silica (5% to 15%) and Ground granulated blast furnace slag (20% to 50%) considering w/b=0.55. A total of twelve ternary mixes and one conventional mix were prepared to identify optimum mix. Flow characteristics and strength properties (compression, modulus of rupture and modulus of elasticity) are determined for both conventional and Ternary mixes at 28 days. Empirical relationships are drawn between Elastic modulus, modulus of rupture and compressive strength for the optimum ternary mix.

Experimental Investigation of Recycled Fine Aggregate from Demolition Waste in Concrete

In this study, locally produced recycled fine aggregate from concrete demolition waste was investigated for potential replacement of sand in new concrete mixes. Tests for the waste material included visual examination, chemical composition, grain size distribution, specific gravity, and fineness modulus. Tests on the incorporated recycled fine aggregate in new concrete mixes involved tests of the hardened plain concrete product. In total, eight concrete mixes were considered, of which four had low cement content with 30 MPa target strength, and the other four had high cement content with 55 MPa target strength. For each cement content, the four concrete mixes incorporated fine aggregate replacement ratios of 0% (control), 25%, 50%, and 100%. The hardened concrete tests involved cubes, cylinders, and prisms. The tests addressed compressive strength, tensile strength, and modulus of rupture in accordance with the relevant ASTM standards. In all cases, the average of two tested samples at the age of 28 days was considered. Results of the study showed that the recycled fine aggregate has some cementitious properties, which is capable of hardening when mixed with water and left to dry, even without adding cement from exterior sources. All tested concrete specimens made with recycled fine aggregate exhibited compressive and tensile strengths at least equal to 75% that of the control specimens that contained natural fine aggregate. However, for concrete mixes utilizing low cement content that can yield a compressive strength around 30 MPa with natural aggregate, replacement of 25% or 100% of the natural fine aggregate by weight with locally produced recycled fine aggregate from crushed old concrete can match and often exceeds the compressive and tensile strength of concrete made with virgin aggregate.

Design of a new 11Cr martensitic steel and evaluation of its long-term creep rupture strengths

A new grade of 11 wt% Cr steel was designed in which no nitrogen was added to minimise the driving force of the Z-phase formation and hence to maximise the stability of the fine MX precipitate particles. But, 6 wt% Co was added to completely suppress the δ-ferrite formation in the matrix. The creep data were measured in the range of 650–725 °C at different stresses and rationalised on the basis of a new creep model, which revealed that the effect of stress on creep was equivalent to that of temperature. The model parameters so determined was used to predict the 100,000 h creep rupture strengths. The results showed that these long-term creep rupture strengths were higher than those for the P92 Steel, which is a 9 wt% Cr and the strongest steel grade among commercial 9–12 wt% Cr steels at present. The reliability of the long-term creep rupture strength predictions for the new steel is also analysed.

Effects of interface bonding on the macro-mechanical properties of microcapsule/epoxy resin composites

Microencapsulated phase change materials (MPCMs) can be used as energy-saving fillers to regulate the temporal and spatial mismatches of thermal energy in many fields. However, the MPCMs/epoxy composites suffer from severe mechanical strength reduction due to the poor interface bonding between microcapsules and epoxy matrix. The present work aims to enhance the microcapsule/epoxy interface mechanical properties to improve the macro tensile strength of composites via chemical modification of the microcapsules. Three silane coupling agents (SCAs) were used to modify the outer surface of n-octadecane@MF microcapsules to introduce covalent bonds at the microcapsule/epoxy interface. Surface modification has little effect on the rupture strengths of individual microcapsules, whereas nanoindentation mapping reveals that the γ-(2, 3-epoxypropoxy) propytrimethoxysilane (EPTMS) modified microcapsule/epoxy interface has enhanced elastic modulus of 4.20±0.08 GPa and nanoindentation hardness of 0.24±0.01 GPa, which are markedly higher than the elastic modulus (3.78±0.18 GPa) and nanoindentation hardness (0.20±0.02 GPa) of matrix. The EPTMS modified microcapsule/epoxy composites exhibit 23.55% higher tensile strength than the unmodified microcapsule/epoxy composites. It demonstrates that enhancing the microcapsule/epoxy interfacial mechanical properties with appropriate SCAs is beneficial to improving the macro tensile strength of the composites.