Residual Bending Strength Research Articles

Preparation, Properties and Growth Mechanism of Low-Cost Porous Si3N4 Ceramics with High Levels of β-Si3N4 Powders

Nowadays, porous Si3N4 ceramics are fabricated by high purity α-Si3N4 powders, resulting in a higher cost of production. To reduce cost and save energy, in this research, high levels of β-Si3N4 powders were effectively utilized to produce excellent and low-cost porous Si3N4 ceramics. The effects of high levels of β-Si3N4 powders on the microstructural evolution and properties were investigated in detail. The results suggested that, with the increase in β-Si3N4 powders from 0 wt.% to 80 wt.%, the aspect ratio of β-Si3N4 grains gradually decreased because of the anisotropic growth of grains significantly impinged by adjacent other β-Si3N4 grains. Additionally, the bending strength and dielectric constant of porous silicon nitride ceramics declined and their values were 685 MPa - 220 MPa, and 7.58–5.57, respectively, while the porosity increased from 5.9% to 28.5%. Similarly, the residual bending strength of Si3N4 ceramics degraded from 615 MPa to 172 MPa at 1000 °C for 20 h owing to the formation of SiO2 on the surface of silicon nitride ceramics after oxidizing.

The High-Velocity Impact Behaviour of Kevlar Composite Laminates Filled with Cork Powder

The literature reports benefits when the cork powder obtained from industrial by-products is used as the filler of composite laminates. For example, while the fatigue life is insensitive to the presence of cork in the resin, significant improvements are achieved in terms of to low-velocity impact strength. However, in terms of ballistic domain, the literature does not yet report any study about the effect of incorporating powdered cork into resins. Therefore, this study intended to analyse the ballistic behaviour and damage tolerance of Kevlar/epoxy reinforced composites with matrix filled by cork powder. For this purpose, high-velocity impacts were studied on plates of Kevlar bi-directional woven laminates with surfaces of 100 × 100 mm2. It was possible to conclude that the minimum velocity of perforation is 1.6% higher when the cork powder is added to the resin, but considering the dispersion, this small difference can be neglected. In terms of damage areas, they are slightly lower when cork dust is added, especially for velocities below the minimum perforation velocity. Finally, the residual bending strength shows that these composites are less sensitive to impact velocity than the samples with neat resin. In addition to these benefits, cork powder reduces the amount of resin in the composite, making it more environmentally friendly.

Evaluation of the mechanical properties of high-strength cement paste at elevated temperatures using metakaolin

This paper presents a wide experimental study, in which it evaluates the performance of high-strength paste exposed to elevated temperatures up to 900 °C. Several factors have been investigated at the age of 90 days, i.e. metakaolin (MK) dosages, water to binder ratio (w/b) as well as elevated temperatures. Results proved that MK improves the relative residual compressive strength and relative residual bending strength showing a gain up to 52% and of 71% at 500 °C, respectively, compared to the pure cement paste in case of 0.3 w/b. The maximum use of MK is not more than 12%, and the optimum dosages were 9, 12, and 12% of MK replacements for 0.3, 0.35, and 0.4 w/b, respectively. The optimum dosage could change with changing w/b ratio and this up to the density of the microstructure which is controlled by the amount of w/b ratio and the packing effect of MK amount. In addition to the mechanical properties, the adoption of MK decreases the cracking of the specimens at elevated temperatures. SEM investigations show the positive physical morphology contribution of MK, specific surface area as well as its chemical composition for decreasing the Ca(OH)2 effect. Different phases that formed during temperatures elevation are illustrated by TG analysis. Results showed the reason behind using MK on the cracking enhancement and mechanical properties improvement after high temperatures exposure. Meanwhile, the obtained optimum MK dosages at ambient temperature are not similar to that obtained at elevated temperatures.

Ablation behaviour and mechanical property of the B-modified SiC/HfC-SiC composites in cyclic ablation environment

The B-modified SiC/HfC-SiC composites were prepared by the combination of precursor infiltration and pyrolysis (PIP) and chemical vapor deposition (CVD) methods. The microstructure, cyclic ablation and bending strength tests of the SiC/HfC-SiC composites with and without B were investigated. The results showed that the B-modified composites had a better cyclic ablation resistance than that of the composites without B. The effective residual thickness of the B-modified composites was also higher than that of the composites without B after cyclic ablation. The residual bending strength of the B-modified composites was slightly lower than that of the composites without B.

Experimental Analysis of Residual Stress and Bending Strength of Gear Tooth Surface after Shot Peening Treatment

The fatigue strength of a gear tooth surface is affected by various factors, which subsequently impacts the transmission performance of gears. Usually, shot peening treatment is carried out during processing to improve the performance of gears. Most current studies focus on theoretical descriptions and simulation analyses of shot peening treatment. However, in this paper, the relationships among shot peening treatment, residual stress, and bending fatigue strength of a gear tooth surface are discussed, through experimental methods. Based on X-ray stress analysis, at select locations on the test samples, the residual stresses on gear tooth surfaces with and without shot peening treatment are determined and contrasted. The results show that shot peening treatment can effectively increase the residual stress on gear tooth surfaces. In addition, an electromagnetic resonance fatigue tester is used to analyze the bending fatigue strength of gear tooth surfaces. The test results indicate that the bending fatigue strength of the gear teeth with shot peening is higher than that of the gear teeth without shot peening. The obtained conclusions lay the foundation for further practical engineering applications of gears.

The effect of low-velocity impact on the flexural strength of E-glass/epoxy composite plates

E-glass/epoxy composite is very prone to small impact such as dropping tools or splash rocks, which can cause damage or degradation to E-glass/epoxy composite components. A progressive damage model for E-glass/epoxy composite in ABAQUS Explicit was developed in this study to numerically predict low-velocity impact (LVI) damage and residual strength of an E-glass/epoxy composite component. Hashin-Rotem criteria were used to define laminate damage initiation, and traction-separation law was used to define the cohesive region. LVI and four-point bending after the impact (BAI) of the woven E-glass/epoxy composite plates were simulated and compared with available experimental data in the literature. Good agreement was found between finite element analysis (FEA) predictions and the experimental results, which include the impact zone shape, as well as the load-deflection response and residual bending strength from the four-point bending tests.

Structural Behavior of High Strength Laced Reinforced Concrete One Way Slab Exposed to Fire Flame

In this study, an experimental investigation had conducted for six high strength laced reinforced concrete one-way slabs to discover the behavior of laced structural members after being exposed to fire flame (high temperature). Self-compacted concrete (SCC) had used to achieve easy casting and high strength concrete. All the adopted specimens were identical in their compressive strength of ( , geometric layout 2000 750 150 mm and reinforcement specifics except those of lacing steel content, three ratios of laced steel reinforcement of (0.0021, 0.0040 and 0.0060) were adopted. Three specimens were fired with a steady state temperature of for two hours duration and then after the specimens were cooled suddenly by spraying water. The simply supported slabs were tested for flexure behavior with two line loads applied in the middle third of the slab (four-point bending test). The average residual percentage of cubic compression strength and splitting tensile strength were 57.5% and 50% respectively. The outcomes indicated that the residual bending strength of the burned slabs with laced ratios (0.0021, 0.004, 0.006) were (72.56, 70.54 and 70.82%) respectively. However; an increase in the deflection was gained to be (11.34, 14.67 and 17.22%) respectively with respect to non-burned specimens.

Performance of composites via multiple interface engineering techniques: plasma etching, UV-induced grafting and nanotube deposition

We systematically investigate interfacial modification mechanisms on interfacial structure, mechanical and anti-fatigue performances of carbon fiber/epoxy (CF/EP) composites. The same interfacial shear strength (IFSS) was achieved by reasonable experiment design based on three explored mechanisms: (i) Ar plasma treatment for mechanical interlocking mechanism, (ii) UV-induced grafting acrylic acid for chemical bonding effect and (iii) carbon nanotubes electrophoretic deposition for transition layer theory. We found that the interface layer thickness and modulus of composites vary greatly due to different interfacial modification mechanisms. The damage resistance can be improved by increasing the propagation paths or hindering the propagation direction of the destructive cracks. Under the condition of the same interfacial strength, the variation trend of mechanical strength and fatigue properties were signfificantly different owing to the different interface microstructure. The nanotube deposition method has advantages in flexural strength, tensile strength and storage modulus, because the formed gradient interface layer has the dual effects of strengthening, toughening resin and increasing stress transfer efficiency. Plasma etching method is superior to the other two methods in residual bending strength retention because the mechanical interlocking in the interface micro-region can improve the stiffness of the composite and hinder the propagation of cracks. UV-induced grafting method is beneficial in improving the tensile strength of composites, because it has low damage to the mechanical strength of fiber. Therefore, when the interfacial strength is the same, carbon nanotubes electrophoretic deposition among the three modification methods has more attractive application prospects.

Effects of SDBS and ZrO2 additives on the microstructure and properties of silicon-bonded SiC porous ceramics

Porous silicon-bonded silicon carbide (SBSC) ceramics were prepared under argon atmosphere, with silicon as pore former and bonding material, simultaneously, sodium dodecyl benzene sulfonate (SDBS) and ZrO2 as sintering additives, the effects of SDBS and ZrO2 on the porosity, pore size, mechanical, physical and thermal properties and microstructures were investigated. The results suggested that suitable content of SDBS and ZrO2 could not only effectively lower the sintering temperature to 1450 °C due to the sticky flow of molten silicon, but also increase the pore structure and improve the bending strength. The reason for this is that SDBS decomposed into Na2O which reacted with ZrO2 and impurity SiO2, which was the native oxide film on the surface of SiC particles, to form a bonding phase between SiC particles to improve the bending strength; meanwhile, the disappearances of impurity SiO2 would benefit the bond of molten silicon and silicon carbide particles, and silicon melt leaving pores in its original position to increase the pore structure. The optimal apparent porosity, bending strength, average pore size, gas permeance and residual bending strength after thermal shock cycles of SBSC porous ceramic sintered at 1450 °C with 5 wt% SDBS and 6 wt% ZrO2 were 38.33%, 55.4 MPa, 11.3 μm, 106.4 m3/m2·h·kPa and 28.2 MPa, respectively.

Damage and residual bending strength in glass-polyester molded grating composite panels after low-velocity impact

Glass-polyester molded grating composites (MGC) are brittle and sensitive to the damage caused by the impact. In this study, a finite element model has been proposed to predict the strength of the molded grating composite panels against low-velocity impact loads. Molded grating composites have unidirectional reinforcement fibers, except in the intersections where behave as a blocked bidirectional reinforced materials. Hashin failure criteria and a proposed sudden degradation model have been employed to distinguish damage initiation and formulate damage evolution, respectively. The proposed degradation rule basically is Tserpes model with a small modification for shear dominant tension-compression degradation. In order to validate the results a series of experimental impact tests were carried out by means of a drop weight tower in different states of the height and mass of the drop weight. Three-point bending tests on the intact specimen and impacted specimens were performed in order to determine the reduction of strength and stiffness after impact. The results show that the numerical analysis based on the proposed modified Tserpes model predicts the ultimate force and the slope of the load-displacement diagram with a reasonable accuracy that correlate well with the experimental results.

MECHANICAL PROPERTIES IMPROVEMENT OF FIBER REINFORCED CONCRETE

Fiber reinforced concrete mechanical properties are limited due to low adhesion between polymer fibers and cement matrix. To ensure a strong interaction between the two materials, polypropylene fibers (d = 0.305mm) were modified by an oxygen plasma treatment. The interface interaction was moreover activated using finely ground concrete recyclate, whose individual grains (1−64 μm) ensure an adhesion improvement in interfacial zones. The adhesion enhancement was verified by pull-out tests, when reference and modified fibers were pulled-out from cement matrix specimens. Such obtained results were used as a crucial parameter to numerical simulations of bending tests of specimens (550 × 150 × 150mm) with properties following fiber reinforced concrete. It was shown that samples reinforced with modified fibers and contained activating recyclate reached on higher residual bending strength then those with reference fibers.

Effect of Co on thermal and mechanical properties of Si3N4 based ceramic tool material

The use of ceramic cutting tools is limited due to their inherent brittleness. In this paper, metal phase Co is considered to strengthen Si3N4 based ceramic tool materials. The effects of Co on room-temperature and high-temperature mechanical properties and thermal shock resistance of the material are studied. Compared with the composite without Co, the addition of Co can improve room-temperature fracture toughness of Si3N4 based ceramic material at the cost of reducing its hardness. The flexural strength decreases a little in accordance with the reduced relative density. As the testing temperature increases, the fracture toughness first increases gradually and then decreases sharply while the flexural strength decreases gradually. Due to the oxidation inhibition effect, the Co-containing composite maintains higher flexural strength and fracture toughness than the Co-free composite at the specified test temperatures. The critical thermal shock temperature difference of the composite with Co is higher than that without Co, although before reaching the difference its residual bending strength is lower due to pores and thermal mismatch effect. The addition of Co can also inhibit the growth of thermal shock microcracks and improve the thermal fatigue resistance of Si3N4 ceramic material.

The preparation of in-situ MoSi2-SiC-MoB three-phase composite completely eliminating the PEST phenomena

Because of high melting point (2300 K), rather low density (6.28g/cm3) and excellent elevated oxidation resistance (above 1600 °C), MoSi2 have been treated to be one of the most attractive high temperature materials. However, thus a MoSi2 materials have their intrinsic limitations, one of the worst things is it suffered from an accelerated oxidation at low temperatures (between 350 and 550 °C) which was first discovered by Fitzer in 1955 and was named PEST oxidation. The phenomena of PEST extremely hindered the application of MoSi2 in advanced engineering and aerospace, also limited its longevity and safety. In this paper, an in-situ MoSi2-SiC-MoB three-phase composite was prepared by reactive infiltration process which is known as low-cost and net shape method, and after the oxidation process in 500 °C for 3 h, it was found that there is no PEST occurred anymore. And the residual bending strength of this composite will still over 68%. The reasons for overcoming PEST would be the in-situ formed MoB phase will be stiffly covered over the surface of MoSi2 grains, and the volume expansion of SiC phase and volume contraction of MoB phase will be matched in the composite system 9.7%wt MoB/8.6%wt SiC/MoSi2.

Experimental Investigation of Residual Ultimate Strength of Damaged Metallic Pipelines

The ultimate strength of metallic pipelines will be inevitably affected when they have suffered from structural damage after mechanical interference. The present experiments aim to investigate the residual ultimate bending strength of metallic pipes with structural damage based on large-scale pipe tests. Artificial damage, such as a dent, metal loss, a crack, and combinations thereof, is introduced to the pipe surface in advance. Four-point bending tests are performed to investigate the structural behavior of metallic pipes in terms of bending moment–curvature diagrams, failure modes, bending capacity, and critical bending curvatures. Test results show that the occurrence of structural damage on the pipe compression side reduces the bending capacity significantly. Only a slight effect has been observed for pipes with damage on the tensile side as long as no fracture failure appears. The possible causes that have introduced experimental errors are presented and discussed. The test data obtained in this paper can be used to further quantify damage effects on bending capacity of seamless pipes with similar D/t ratios. The comparison results in this paper can facilitate the structural integrity design as well as the maintenance of damaged pipes when mechanical interference happens during the service life of pipelines.

Experimental Study on Residual Bending Strength of Corroded Reinforced Concrete Beam Based on Micromagnetic Sensor.

This paper presents a nondestructive test method to evaluate the residual bending strength of corroded reinforced concrete beam by analyzing the self-magnetic flux leakage (SMFL) signals. The automatic scanning device was equipped with a micromagnetic sensor and sensor-based experimental details were introduced. Next, the theoretical formula of the normal component HS(z) of the SMFL signal that originated from the corroded region was derived based on the magnetic dipole model and the experimental results were discussed. The results indicate that the experimental data of HS(z) are consistent with the theoretical calculations, both location and extent of the steel bars corrosion can be qualitatively determined by using HS(z). The gradient K of HS(z) is approximately linearly related to the loss rate, S, of the bending strength, which can be used to evaluate the residual bending strength of the corroded reinforced concrete beam. This work lays the foundation for evaluating the residual bending strength of corroded reinforced concrete beams using the SMFL signal; the micromagnetic sensor is further applied to the civil engineering.

Oxidation degradation and mechanical reduction on C/SiC composites with artificial notch defects

Continuous carbon fiber reinforced silicon carbide matrix composites (C/SiCs) have been widely used in aeronautic and astronautic fields because of their more attractive high temperature properties with less structural weight. However, reinforcing carbon fibers are susceptible to oxidation especially when the notch defects (ND) expose them to air. Mechanical tests, microstructural characterization combined with computed tomography (CT) were performed to explore the effect of the ND on the oxidation behavior and residual properties of the C/SiCs. Results showed that, before oxidation, the remaining bending strengths of the C/SiCs with even 5 ND numbers maintained still above 93%, indicating that increase of the ND numbers had little effect on mechanical properties. However, after oxidation at 700 °C, weight loss ratio of the C/SiCs with the ND numbers of 0, 1, 3 and 5 increased from 1.01% to 3.73%. It suggested that the more the ND numbers, the greater the proportion of carbon fiber exposed to air, and the less the oxidation resistance. Meanwhile, the residual bending strength remaining ratio of the C/SiCs largely reduced from 83.7% to 60.7% with the increase of ND numbers. It pointed out that the ND induced oxidation degradation of the reinforcing fiber caused higher sensitivity to the mechanical strength of the C/SiCs, and with the increase in the ND numbers, the strengths decreased more obviously.

Bending capacity of corroded welded hollow spherical joints

Welded hollow spherical joints (WHSJ) have been widely used in space lattice structures. Corrosion is inevitable in the service life of WHSJ, which significantly reduces their bending capacity and seriously threatens their structural safety. This study aims to investigate the influence of corrosion that occurred at different places on the bending stiffness and bending capacity of WHSJ. The effects of corroded location and size, corroded thickness, and diameter and thickness of spherical body were investigated through a series of nonlinear numerical analyses. Two types of corroded shape were investigated. The equation used for predicting the residual bending stiffness of corroded WHSJ was established. Results indicated that corrosions in different places had distinct influence on the bending capacity of WHSJ. Loading capacity could be significantly reduced when corrosion occurred at other areas. The derived results would provide a foundation for estimating the residual bending stiffness and strength of structures connected by corroded WHSJ.

Analysis of composite stiffener under successive impact and bending test

In this article, we present the analysis, modelling and experimental investigation of composite omega stiffeners from non-penetrating impact to bending-after-impact. We used advanced computational methods to determine the extent of damage due to impact and, without many simplifications to the damage, predict the residual bending-after-impact strength under four-point-bend tests. The predicted sizes and patterns of impact damage, and the subsequent predicted bending strengths are compared to experimental tests of omega stiffeners. This work shows that preserving the details and fidelity of damage in the computational model is critical to successful prediction of residual strength. It was also found that modifying the design of the stiffeners by changing the orientation of some of the plies reduces the extent of impact damage and increases residual bending strength.

Effect of high temperature cycling on both crack formation in ceramics and delamination of copper layers in silicon nitride active metal brazing substrates

Crack formation in Si3N4 active metal brazing (AMB) ceramic substrates and delamination of copper layers on the AMB substrates subjected to temperature cycling from −40 to 250°C were investigated to evaluate the reliability of these substrates under harsh environments. Acoustic scanning microscopy (ASM) observation of the Si3N4 substrates with 0.30mm thick Cu layers revealed crack formation beneath the corner of the copper plate after 100 cycles, whereas no cracks were detected on the Si3N4 substrate with a 0.15mm thick Cu layer, even after 1000 cycles. The residual bending strength of the Si3N4 substrates with 0.30mm thick Cu layers was 78% of the as-received substrate after 10 thermal cycles, and gradually decreased with an increase in the number of thermal cycles until ca. 65% of the initial strength after 1000 cycles. The Si3N4 substrates with 0.15mm thick Cu layers exhibited a gentler degradation of residual strength than those with 0.30mm thick Cu layers. In contrast, the residual bending strength of AlN-AMB substrates with 0.15mm or 0.30mm thick Cu layers were reduced by 50% within only 10 thermal cycles. The depth of cracks developed during the thermal cycles was measured from the fractured surface of the Si3N4-AMB and AlN-AMB substrates. The crack-growth rate in the Si3N4-AMB substrates was much slower than that in the AlN-AMB substrates, which could account for the different degradation behavior of the residual bending strength.

Preparation and performance study of cordierite/mullite composite ceramics for solar thermal energy storage

AbstractThe employment of solar energy in recent years has reached a remarkable edge. It has become even more popular as the cost of fossil fuel continues to rise. Energy storage system improves an adjustability and marketability of solar thermal and allowing it to produce electricity in demand. This study attempted to prepare cordierite/mullite composite ceramics used as solar thermal storage material from calcined bauxite, talcum, soda feldspar, potassium feldspar, quartz, and mullite. The thermal physical performances were evaluated and characterized by XRD, SEM, EPMA, and EDS. It was found that the optimum sintering temperature was 1280°C for preparing, and the corresponding water adsorption was 11.25%, apparent porosity was 23.59%, bulk density was 2.10 mg·cm−3, bending strength was 88.52 MPa. The residual bending strength of specimen sintered at 1280°C after thermal shock of 30 times decreased to be 57 MPa that was 36% lower than that before. The thermal conductivity of samples sintered at 1280°C was tested to be 2.20 W·(m·K)−1 (26°C), and after wrapped a PCM (phase change materials) of K2SO4, the thermal storage density was 933 kJ·kg−1 with the temperature difference (ΔT) ranged in 0‐800°C. The prepared cordierite/mullite composite ceramic was proved to be a promising material for solar thermal energy storage.