基于深度学习的平纹Cf/SiC复合材料原位拉伸损伤演化与断裂分析

为揭示平纹C_f/SiC复合材料的拉伸损伤演化及失效机理,开展了X射线CT原位拉伸试验,获得材料的三维重构图像,利用深度学习的图像分割方法,准确识别出拉伸裂纹并实现其三维可视化。分析了平纹C_f/SiC复合材料损伤演化与失效机理,基于裂纹的三维可视化结果对材料损伤进行了定量表征。结果表明:平纹C_f/SiC复合材料的拉伸力学行为呈现非线性,拉伸过程中主要出现基体开裂、界面脱黏、纤维断裂及纤维拔出等损伤;初始缺陷易引起材料损伤,孔隙多的部位裂纹数量也多;纤维束外基体裂纹可扩展至纤维束内部,并发生裂纹偏转。基于深度学习的智能图像分割方法为定量评估陶瓷基复合材料损伤演化与失效机理提供了有效分析手段。     

Laboratory investigation of cracking resistance performance of the cold-mixed epoxy resin

Cold-mix epoxy resin (CER) is an excellent binder material but with weak crack resistance and brittle failure risk. Therefore, it is of significance to find a feasible parameter to constrain the failure potential. To this end, the dynamic mechanical test, tensile test, volume shrinkage test, fracture test, and scanning electron microscopy (SEM) were used to analyze and evaluate mechanical properties, curing shrinkage, and fracture toughness of the CER. Subsequently, the bivariate correlation analysis was used to feature the relationship among different indicators. The results indicated that the amount of curing agent has a significant influence on the tensile strength, elongation at break, volume shrinkage, fracture toughness, and plastic radius of CER. Meanwhile, there is a close correlation between tensile strength, elongation at break, and fracture toughness. Fracture toughness can be used as an evaluation index to represent the crack resistance of CER, and tensile test can be used as a confirmatory parameter. However, the volume shrinkage of CER cannot be ignored. Small voids distributed on the fracture surface of the CER can increase the toughness and then improve the crack resistance of the CER through SEM analysis.     

In Situ X‐Ray Diffraction and Stress Analysis of Solid Oxide Fuel Cells

To increase the long term stability and performance of solid oxide fuel cell (SOFC) materials, it is important to understand the main degradation processes in their functional layers. In this work, the interface between electrolyte and anode material was investigated by in situ X‐ray diffraction (XRD) stress and phase analysis. It has been found that the determining process for the initial degradation of SOFC is the reduction of the anode material with hydrogen. During this process a tensile strength of 600–700 MPa is measured. These stresses are induced in the electrolyte material and produce crack networks. The reduction from nickel oxide to pure nickel was monitored by in situ phase analysis. This reaction induces tensile stress at the interface between electrolyte and anode. The stress produced in the electrolyte material was also confirmed by the observation of crack networks detected using scanning electron microscopy (SEM). Finally, the reducing process was optimized using different process gases, decreasing the destructive tensile stress level.     

Monotonic tension behavior of 2D woven oxide/oxide ceramic matrix composites at ultra-high temperature

The research on mechanical behavior and failure analysis of oxide/oxide CMC at ultra-high temperatures can broaden its application scope. The present work studied monotonic tension behavior of the oxide/oxide CMC at 800 °C～1200 °C and two tensile rates (i.e. 5 mm/min and 0.5 mm/min). The uniaxial tensile test, fracture morphology characterization and finite element analysis were preformed to reveal the deformation and failure mechanisms of the oxide/oxide CMC at ultra-high temperature. The results show that the mechanical properties of the oxide/oxide CMC are sensitive to the temperatures and tensile rates. The stress-strain curves are almost linear at the high tensile rate and nonlinear at the low tensile rate. The ultimate tensile strength decreases significantly at low tensile rate and for temperatures higher than 1100 °C. The mechanical properties of the material are principally determined by oxide fiber/oxide matrix interface strength under low temperature and high-stress conditions, while by interlayer bonding strength under high temperature and low-stress conditions.     

Development of gypsum-based composites with tensile strain-hardening characteristics

Brittle nature of gypsum restrains its wide application in construction industry. For improvement, a novel type of composite material, gypsum-based engineered cementitious composites (GS-ECC), was developed using specially chosen polyethylene (PE) fibers. This study investigated the rheological and mechanical properties of GS-ECC, that is, workability, uniaxial tensile and compressive behavior, flexural strength, etc The investigation showed that GS-ECC possessed excellent tensile strain-hardening behavior and saturated cracking characteristics with the average tensile strain capacity more than 5%. To explore the underlying mechanism, the microstructure of interface transition zone (ITZ) between gypsum crystals and PE fibers were investigated through the use of SEM. Single fiber pull-out test, bending-fracture test, and single crack tension test were conducted to investigate the mesoscopic properties from fiber/matrix interface to matrix toughness and fiber bridging capacity. This study demonstrates the feasibility of achieving strain-hardening gypsum-based composites by adding the PE fibers.     

NEPE推进剂拉伸断裂行为研究

通过单向拉伸力学性能实验,考察了不同测试温度和不同拉伸速率条件下NEPE推进剂力学性能的变化情况。采用扫描电镜(SEM)和原位拉伸SEM观察了推进剂拉伸断面形貌。结果表明,在低温测试条件下,NEPE推进剂最大伸长率较常温条件下显著降低,最大抗拉强度较常温和高温条件下显著升高,NEPE推进剂的破坏主要表现在黏合剂的撕裂和固体颗粒的断裂;在高温、慢拉伸速率的测试条件下,推进剂断裂时结构被破坏的程度较大,NEPE推进剂的破坏首先发生在固体颗粒堆积处,再到黏合剂网络结构。推进剂断裂的过程是推进剂拉伸取向与裂纹扩展之间的竞争过程。     

In-situ characterization on crack propagation behavior of SiCf/SiC composites during monotonic tensile loading

The microstructure and crack propagation path of 2.5D SiC_f/SiC composites were observed by synchrotron radiation x-ray computed micro tomography (SR-μCT) equipped with in-situ tensile device. The results showed that the pore morphologies of the SiC_f/SiC composites are mainly divided into three types in three-dimension space: interconnected pores, isolated pores and micro pores in fiber bundles. The crack initiation occurred at the root of the defects under in-situ tensile load and the crack was perpendicular, parallel to the stress axis or mixed mode to propagate. At the interface scale between fiber and matrix, the crack deflection will be controlled by physical parameters such as fracture energy release rate and the modulus of elasticity. At the fiber bundle scale, the crack is easy to shear propagate along the interface between weft and warp fiber bundles due to the existence of the mechanical bonding and residual tensile stress.     

聚硫密封剂浸油后拉伸断裂行为分析

研究了聚硫密封剂浸航空煤油后的断裂行为,对在3号航空煤油中浸渍不同时间(0、24、48、120、168h)的聚硫密封剂进行了拉伸性能测试,采用扫描电子显微镜,对拉伸断裂试样进行了断口观察,并对聚硫密封剂的断裂特征形成原因进行了分析.研究表明:密封剂拉伸时,裂纹形成、扩展到最后试样断裂,其过程可分为裂纹慢速扩展和快速断裂...     

Volumetric assessment of fatigue damage in a SiCf/SiC ceramic matrix composite via in situ X-ray computed tomography

To enhance the understanding of matrix cracking and damage progression on the macroscopic scale, within a 0/90° fibre reinforced SiC_f/SiC ceramic matrix composite (CMC), X-ray computed tomography (XCT) imaging and analysis have been performed in conjunction with a commercially available in-situ mechanical loading device. CMC test coupons were subjected to tensile cyclic loads and inspected using XCT without removal from the tensile loading device. Attempts to measure and quantify the resulting damage using volumetric image analysis techniques are presented, by characterising the crack network from XCT images acquired at both the maximum and minimum load condition during selected fatigue cycles. The XCT detection of significant crack development within the first loading half-cycle shows good agreement with cumulative acoustic emission energy data recorded under similar test conditions. The results are seen as an important step towards correlating the damage behaviour detected via different NDE and health monitoring techniques.     

Effects of gradual matrix crack closure on the constitutive behavior of SiC/SiC composites upon unloading

Gradual matrix closure and its effects on the constitutive behavior of SiC/SiC composites are examined in the present study. Real-time matrix crack detection and a macroscopic loading–unloading tensile test are performed on SiC/SiC minicomposites. To verify the effects of matrix crack closure, stress-strain responses under loading and unloading with and without crack closure are discussed. The experimental and numerical results show that matrix cracks close gradually upon unloading, and gradual matrix closure greatly reduces the unloading stiffness.     

Direct assessment of tensile stress-crack opening behavior of Strain Hardening Cementitious Composites (SHCC)

The process of designing Strain Hardening Cementitious Composites (SHCC) is driven by the need to achieve certain performance parameters in tension. These are typically the pseudo-strain hardening behavior and the ability to develop multiple cracks. The assessment of the tensile load-deformation behavior of these materials is therefore of great importance and is frequently carried out by characterizing the material tensile stress–strain behavior. In this paper an alternative approach to evaluate the tensile performance of SHCC is investigated. The behavior of the material in tension is studied at the level of a single crack. The derived tensile stress-crack opening behavior is utilized to analyze and compare the influence of various composite parameters on the resulting tensile behavior. The deformations occurring during tensile loading are furthermore examined using a digital image-based deformation analysis technique to gain detailed insight into the crack formation, propagation and opening phases.     

Fatigue and Static Crack Propagation in Yttria-Stabilized Tetragonal Zirconia Polycrystals: Crack Growth Micromechanisms and Precracking Effects

The influence of precracking techniques in the crack growth behavior of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is investigated. Load-bridge and cyclic-compression precracking enhance subsequent tensile crack growth rates, in comparison to results that are found with precracks that are extended under four-point bending prior to testing. The actual influence of these precracking techniques in the near-threshold crack growth regime is remarkably different. Although load-bridge precracking produces a pattern of crack growth fluctuations for stress intensity factors, K , lower than the effective crack-growth threshold of the material, compression-fatigue precracks start to propagate under far-field tensile loads at very fast growth rates and for K values that are slightly higher than the effective threshold. Crack-tip shielding by tetragonal-to-monoclinic transformation develops gradually, influencing the crack growth behavior in Y-TZP. Proposed fatigue crack growth micromechanisms involve damage accumulation at the crack-tip region. For K _max > 3 MPa·m^1/2, fatigue crack growth rates are strongly affected by environmental interactions at the crack tip, and postulated fatigue micromechanisms include the cyclic degradation of crack-tip shielding.     

Mechanical properties of graphene oxide reinforced alumina matrix composites

Graphene oxide (GO) reinforced alumina matrix composites have been fabricated by using graphene oxide synthesized by a modified Hummer's method. Samples were prepared by powder metallurgy and consolidated by Spark Plasma Sintering (SPS). The influence of GO addition on the microstructure and mechanical properties of the composites was investigated. Results show a significant increase (almost 35%) of the fracture toughness for composites containing 0.5 wt% graphene oxide compared to sintered pure alumina. In order to find reasons for this improvement Scanning/Transmission Electron Microscopy (SEM/TEM) observations were carried out. They reveal a good interface between the reinforcement and the matrix as well as such mechanisms like branching, deflection and bridging of crack propagation.     

Characterization and modeling of transverse micro-cracking during pyrolysis process of carbon fiber reinforced plastics

The paper presents characterization and modeling of generation of cracks during pyrolysis process of manufacturing of C/C–SiC material. Crack patterns during pyrolysis strongly depend on the fiber/matrix interface strength and temperature. In order to model the exact crack pattern as in the material, fiber/matrix interface strength was taken as a varying parameter and temperature change boundary conditions were applied on a virtual microstructure (50 × 50 μm²). The resulting crack pattern is then compared with SEM images of material with high and low fiber/matrix interface strength. The presented models are successfully able to simulate the material behavior and the consequent generation of cracks during pyrolysis process. Microstructure of the material has been then analyzed with the help of image segmentation techniques using Python. Based on the crack area distribution obtained from the SEM-analysis, microstructures can now be compared qualitatively as well as quantitatively.     

Infrared imaging of stress-crazing in rubber modified polystyrene

The plastic yield and fracture of rubber-modified polystyrene specimens under tensile load have been investigated at room temperature. The experimental procedure consisted of rapidly alternating measurements of transmitted and emitted infrared (IR) radiation from samples under tensile stress. The load-displacement data were simultaneously recorded. Both single-edge-notched and dog bone-shaped test coupons were studied. In each tensile test run, we observed a significant decrease of material transparency in the IR which occurred near the low yield point. A further increase in material deformation was accompanied by a substantial temperature increase. After material failure, the surface morphology of the test specimens in the vicinity of the crack was examined using atomic force microscopy (AFM). Our results are explained in the context of existing models of material crazing.     

Effects of Gelatin and Nano-ZnO on the Performance and Properties of Cellulose Acetate Water Membranes

Biodegradable cellulose acetate (CA) membranes were prepared via phase inversion induced by immersion precipitation method. Acetic acid and deionized water were used as solvent and non-solvent, respectively. The modifying effect of gelatin and zinc oxide (ZnO) nanoparticles additives was investigated on the membranes in terms of water flux, protein rejection percentage, and fouling ability during two hours of bovine serum albumin separation from aqueous solution. Specimens were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), tensile test, contact angle technique, and porosity measurement. The incorporation of gelatin and ZnO nanoparticles into the CA matrix increased the porosity coefficient and hydrophilicity. Moreover, gelatin improved the tensile properties of the membrane.     

Tensile test of poly(vinyl chloride) filled with ground calcium carbonate particles

The fracture behavior of poly(vinyl chloride) filled with ground calcium carbonate particles during a tensile test was studied. The particles were prepared by crushing natural raw crystalline limestone. For this purpose, 10–50 parts of the particles having two different mean sizes (2 and 8 μm) without further surface treatment were mixed with 100 parts of poly(vinyl chloride) and 3 parts of lead stearate as a stabilizer using a mixing roll. A tensile test was carried out using a dumbbell specimen. As a result, the yield stress decreased with increase in the particle content; however, there was no significant influence of particle size. From scanning electron microscopic observations of the specimen's surfaces during the tensile test, it was found that the particle/matrix interfaces were delaminated and formed voids around the particles when the applied stress approached the yield stress, that is, the particles acted as voids and the matrix around the voids was plastically deformed effectively. These observations appear to be the reason for the decrease of yield stress by the incorporation of the particles. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 311–316, 1998     

基于同心环形缝隙流理论的纤维编织网增强混凝土抗渗性能研究

通过对压力水作用下纤维编织网增强混凝土(TRC)的渗透试验和扫描电镜(SEM)试验,探究不同水灰比、纤维单丝含量对TRC试件抗渗性能及内部细观结构的影响。研究表明,自由水在压力作用下沿着混凝土基体与纵向纤维束的界面进行定向迁移,TRC的抗渗性能随水灰比及纤维单丝含量增大而减弱。此外,SEM试验表明,混凝土基体与纤维束的界面存在环形裂隙,裂隙宽度随水灰比及纤维单丝含量增大而增大。基于同心环形缝隙流理论,建立压力水作用下TRC试件渗透率的计算公式,计算结果与试验值吻合较好。     

Mechanical properties of high ductile alkali-activated fiber reinforced composites incorporating red mud under different curing conditions

Red mud (RM) is an industrial by-product created during the production of alumina/aluminium that has engendered severe environmental concerns arising from its improper disposal. To mitigate the negative environmental impact of RM waste and produce a sustainable material having high mechanical performance (particularly ductility) for a variety of applications, this study developed an alkali-activated fiber reinforced composite (AAFRC) using RM, ground granulated blast-furnace slag (or slag), and silica fume as the precursors. The effects of two different curing conditions (ambient-curing and heat-curing) on the mechanical properties and microscopic characteristics of the material were systematically investigated. The heat-cured RM-derived AAFRC exhibited excellent tensile strain capacity (or ductility) of up to 5.6%, which was significantly higher than that of its counterpart that was cured under ambient condition. Despite the reduction in strength caused by heat-curing, AAFRC retained adequate tensile and compressive strengths of 4.0 and 75 MPa, respectively. The results of three-point bending, single crack tensile, and single fiber pullout tests provided reasonable explanations for the tensile behaviors of the studied material. Scanning electron microscopy revealed that a less compacted matrix was formed in the RM composite due to heat-curing. The combined results from energy dispersive spectroscopy and nanoindentation tests indicated that adding red mud did not alter the types of reaction products for the material, which were similar in composition to conventional alkali-activated slag while also including C-A-S-H and N-A-S-H gels in addition to a type of layered double hydroxide. These findings can serve as theoretical guidelines for the future design and application of eco-friendly, high-ductile cementless composites prepared from RM waste.     

The effects of functional azo initiator on PMMA and polyurethane IPN systems. III. Tear resistance and crack growth of PBD(1,2)-PU/PMMA (50%) blends

The tear strength and crack growth mechanism of PBD(1,2)–PU/PMMA (50%) IPN systems were studied by the trouser tear test and single edge notched (SEN) tensile test. It was found that these blend systems showed similar structures and properties to particulatereinforced elastomers. The tear strength was dominated by the structure of the rubber matrix. The PMMA phase increased the tearing resistance by increasing the hysteresis of the IPN systems. Chemical bonding between the PMMA-rich particle and PU-rich matrix prepared by using a reactive azo initiator inhibited the initiation of the fracture nucleus, decreased the intrinsic flaw size, and increased the tear strength. The crack growth of these IPNs was dependent on both the fracture energy available for crack propagation and the hysteresis of the material. The similar structure of these two blends resulted in the similar crack growth behavior.