Fiber Failure Modes Research Articles

Fatigue deformation behavior and fiber failure mechanism of ultra-high toughness cementitious composites in compression

Ultra-high toughness cementitious composites (UHTCCs) belong to a family of fiber-reinforced cementitious composites with strain-hardening behavior under tension. Such composites have potential application in structures sustaining fatigue loads. In this paper, the compressive fatigue deformation behavior of UHTCC under various stress levels S (S = 0.90, 0.85, 0.80, 0.75, 0.70 and 0.65) was investigated. It is found that the stress level has little influence on the cyclic creep curve of UHTCC, while the fatigue failure strain increases as the stress level decreases. The failure strains at different stress levels obey the two-parameter Weibull distribution, and a probabilistic model is proposed to consider the effect of stress level on the fatigue failure strain. Using X-ray computed tomography and a scanning electron microscope, three fatigue-induced failure modes of polyvinyl alcohol fibers in UHTCC are found and the possibility for further improvement of the compressive fatigue performance is discussed.

Determination of the crack resistance curve for intralaminar fiber tensile failure mode in polymer composites under high rate loading

This paper presents the determination of the crack resistance curve of the unidirectional carbon-epoxy composite material IM7-8552 for intralaminar fiber tensile failure under dynamic loading. The methodology, proposed by Catalanotti et al. (2014) for quasi-static loading conditions, was enhanced to high rate loading in the order of about 60 s−1. Dynamic tests were performed using a split-Hopkinson tension bar, while quasi-static reference tests were conducted on a standard electromechanical testing machine. Double-edge notched tension specimens of different sizes were tested to obtain the size effect law, which in combination with the concepts of the energy release rate is used to measure the entire crack resistance curve for the fiber tensile failure mode. Digital image correlation is applied to further verify the validity of the experiments performed at both static and dynamic loading. The data reduction methodology applied in this paper is suitable for intralaminar fiber failure modes without significant delamination. Sufficient proof is given that quasi-static fracture mechanics theory can also be used for the data reduction of the dynamic tests. It is shown, that the intralaminar fracture toughness for fiber tensile failure of UD IM7-8552 increases with increasing rate of loading.

Study of random fatigue behavior of C/SiC composite thin-wall plates

As an alternative method of acoustic experiment, vibration tests of C/SiC thin-wall plates were conducted to study the random fatigue behavior. The vibration specimen was clamped with cantilever boundary and subjected to limited-bandwidth vibration excitation. The strain history and fundamental frequency of the specimens were monitored during the vibration test. It was found that the measured strain value and strain amplitude value accorded with Gauss and Rayleigh distribution, respectively. The fundamental frequency decreased greatly when the vibration specimen failed, which could be recognized as failure criterion for the specimen under random loading. The microscopic fracture morphologies showed that the majority failure mode of fibers in the longitudinal and transverse directions were fiber pull-out and fiber splitting, respectively. The tensile force induced by reversed bending load is the main driving force for damage in specimen.

Numerical simulation of Failure Behaviors of CFRP laminates on Hashin model coupled with cohesive elements

The failure modes of carbon fiber reinforced composites (CFRP) was investigated in this study. A method of combination of Hashin model and cohesive elements was proposed to predict failure behaviors in T300/PR319 and AS carbon/epoxy laminates by FE model, while executing three-point bending test. The result shows that there are differences between the response of two materials during bending test. Fiber compression and matrix tension in T300/PR319 and AS carbon/epoxy appears first relatively. Subsequently delamination occurs in AS carbon/epoxy as a result of cohesive elements. A evaluating method of measuring fracture process displacement was also proposed under new damage criterion.

A Review on Acoustic Emission Characterization of Failure Modes of Carbon Fiber Reinforced Composites

Among various composites available for use, carbon fiber reinforced composite is unique in its Nature. Carbon fiber is an extremely strong thin fiber made by pyrolyzing synthetic fibers, such as rayon, until charred. High Strength Composites are made from this fiber by using appropriate matrix material mostly Epoxy resins are used. High Strength, stiffness, light weight and high thermal conductivity are the main advantages over the other composites. Making products with one single composite sheet is not possible always. Some of the intricate or complex shape making is required for joining of two composite sheet. The composites joining can be done in three ways mainly Adhesive, Riveting and Hybrid. Based on the Review among all these joints adhesive joining gives better economic solution in joining. Experimental results point to significant influence of fibre on mechanical properties of sample. The tensile test of the acoustic signal emission (AE) to identify the current state of material integrity in real time. Acoustic system signal correlated to damage events. The carbon fiber composite characteristic failure mechanisms are initiated on the microscale and result in a spontaneous release of elastic energy in terms of mechanical stress waves, the so-called acoustic emissions.

Compressive damage of three-dimensional random fibrous ceramic materials: A meso-mechanics modeling and experimental study

Compression tests and corresponding simulations are performed to investigate the evolution (including damage, fiber–fiber contact, and compaction) of the microstructure of a transversely isotropic three-dimensional (3D) random fibrous (RF) material under compression along the through-thickness direction. A meso-mechanics model of the 3D RF material is built according to scanning-electron-microscope photographs and used for finite-element simulation. We consider two fiber failure modes: brittle fracture and instability. The fiber-fiber contact effect is a key aspect to be considered in simulating the mechanical behavior of a random fibrous network under compression. A new method for simulating the fiber-fiber contact effect is proposed that overcomes the disadvantages of the nonlinear-spring method. The trend of the simulated stress-strain curve agrees well with our experimental results. Progressive damage is found in the damage process, and we find a new damage mode: layer-by-layer damage. We find that the fiber-fiber contact process lags behind the damage process. We analyze the line density of 3D RF material in the damage process and find local compaction within the yield plateau. The formation mechanism of the yield plateau in the stress-strain curve is analyzed.

Tensile fatigue behavior of fiber-reinforced cementitious material with high ductility: Experimental study and novel P-S-N model

Fiber-reinforced cementitious material with high ductility is a cement-based material with strain-hardening behavior under tension, and has potential application in structures sustaining fatigue loads. In this study, the tensile fatigue behavior of this material at various stress levels (S = 0.90, 0.85, 0.80, 0.75, 0.70, and 0.65) is investigated with the stress ratio of 0.1. The fatigue crack pattern, deformation, failure surfaces, and fiber failure modes are analyzed. Four stages are observed in the evolution curve of fatigue deformation. This is different from the three-stage curve of conventional concrete. “Smooth” and “rough” areas are distinguished on the fatigue failure surfaces with different fiber failure modes. Emphasis is placed on the development of a novel probabilistic model. On the basis of the initial distribution of static strength, P-S-N (probability of failure-stress level-fatigue life) models are proposed for a reliable application of this material. Moreover, a suggestion to improve the fatigue life of this material at low stress levels is provided.

Flexural Progressive Failure of Carbon/Glass Interlayer and Intralayer Hybrid Composites.

The flexural progressive failure modes of carbon fiber and glass fiber (C/G) interlayer and intralayer hybrid composites were investigated in this work. Results showed that the bending failure modes for interlayer hybrid composites are determined by the layup structure. Besides, the bending failure is characterized by the compression failure of the upper layer, when carbon fiber tends to distribute in the upper layer, the interlayer hybrid composite fails early, the failure force is characterized by a multi-stage slightly fluctuating decline and the fracture area exhibits a diamond shape. While carbon fiber distributes in the middle or bottom layer, the failure time starts late, and the failure process exhibits one stage sharp force/stress drop, the fracture zone of glass fiber above the carbon layers presents an inverted trapezoid shape, while the fracture of glass fiber below the carbon layers exhibits an inverted triangular shape. With regards to the intralayer hybrid composites, the C/G hybrid ratio plays a dominating role in the bending failure which could be considered as the mixed failures of four structures. The bending failure of intralayer hybrid composites occurs in advance since carbon fiber are located in each layer; the failure process shows a multi-stage fluctuating decline, and the decline slows down as carbon fiber content increases, and the fracture sound release has the characteristics of a low intensity and high frequency for a long time. By contrast, as glass fiber content increases, the bending failure of intralayer composites is featured with a multi-stage cliff decline with a high amplitude and low frequency for a short-time fracture sound release.

Influence of fiber inclination angle on bond-slip behavior of different alkali-activated composites under dynamic and quasi-static loadings

This study investigates the influence of inclination angle (0° and 45°) on the interfacial bond-slip behavior of macro steel fibers (straight, hooked end-deformed and length-deformed) and length-deformed polypropylene fibers reinforced in fly-ash and metakaolin based alkali-activated composites (AACs) under quasi-static and dynamic loadings. AACs demonstrate superior peak bond strength and toughness compared to cement composites regardless of fiber type and loading rate. Results also show that straight steel fiber exhibits a complete pullout in AACs. The amount of deformation of the fibers (deformation ratio) determined the failure type at different inclination angle and loading rate, thus governing the peak load and energy absorption. Depending on the fiber orientation, premature fiber rupture or matrix cracking is observed under dynamic loading in AACs due to matrix brittleness. The fiber failure modes in dynamic pullout are no different from those observed in the quasi-static pullout in AACs.

Compressive failure of fiber reinforced polymer composites – A fractographic study of the compression failure modes

The fractographic aspects of compression failures remain inadequately explored, mainly due to the damages that the compressive load promotes on the fracture surfaces, which difficult the identification of fracture aspects. In addition, despite the large quantity of studies on the literature, there is no consensus concerning the existing compressive failure modes. Aiming to contribute in this research field, this paper has the objective of proposing a novel classification for the compressive failure modes of fiber reinforced polymer composites. The classification proposed here was based on an extensive literature review as well as in microscopic investigations performed on different composite laminates via scanning electron microscopy. It can be said that this classification has a phenomenological nature, since the failure modes were grouped according to the dominant characteristic. Furthermore, the sequence of events that lead to failure was described for each failure mode. This approach eases its application and allows its use for different types fiber composites, besides allowing the investigation of failed composite structures by means of post-mortem analyses. Finally, the wedge splitting failure mode was identified for the first time on fiber reinforced polymer composites.

Damage processes of polypropylene fiber reinforced mortar in different fiber content revealed by acoustic emission behavior

The performances of the cement-based materials can be improved by the incorporation of polypropylene fiber, but the damage processes become more complex with different fiber contents at the same time. The acoustic emission (AE) technology can achieve the global monitoring of internal damage in materials. The evolution process of failure mode and damage degree of polypropylene fiber reinforced mortar and concrete were analyzed by measuring the AE energy, RA value, AF value and b value. It was found that the cement matrix cracked on the initial stage, the cracks further developed on the medium stage and the fibers were pulled out on the last stage. The matrix cracked with minor injury cracks, but the fiber broke with serious damage cracks. The cumulative AE energy was proportional to the polypropylene fiber reinforced concrete and mortar’s ductility. The damage mode and damage degree can be judged by identifying the damage stage obtained by the analysis of the AF value.

Intralaminar fracture toughness of UD glass fiber composite under high rate fiber tension and fiber compression loading

Automotive and aeronautical composite structures can be subjected to dynamic loading scenarios (e.g. crash, bird strike). In both industrial areas, energy-based damage models for composite materials, able to predict initiation and evolution of damage of a composite ply under various loading conditions, are increasingly used. These models require the specification of fracture toughness parameters for the main failure modes. In previous works [1],[2], the authors have successfully enhanced a methodology suggested by Catalanotti et al. [3],[4] to measure the fiber failure crack resistance curves of a UD carbon fiber composite under dynamic loading. This methodology uses the relation between the energy release rate, the crack resistance curve and the size-effect law. For the determination of the size-effect law, double-edge-notched specimens of different sizes are tested. In this work, the developed approach is used for the measurement of the fracture toughness for fiber tension and compression failure of a UD glass-epoxy composite under high rate loading. Static tests are performed on an electromechanical test machine. For the high rate tests, split-Hopkinson bars for tensile (SHTB) and compressive (SHPB) loading are used. The results show, that the fracture toughness of the UD glass-epoxy composite, associated with the fiber failure modes, increases with increasing loading rate for tension as well as for compression. The observed strain rate effect on the fracture toughness of the glass-epoxy composite is more pronounced than for the carbon-epoxy composite investigated in [1],[2], in particular for fiber tensile failure.

Crack Propagation Calculations for Optical Fibers under Static Bending and Tensile Loads Using Continuum Damage Mechanics.

Static fatigue behavior is the main failure mode of optical fibers applied in sensors. In this paper, a computational framework based on continuum damage mechanics (CDM) is presented to calculate the crack propagation process and failure time of optical fibers subjected to static bending and tensile loads. For this purpose, the static fatigue crack propagation in the glass core of the optical fiber is studied. Combining a finite element method (FEM), we use the continuum damage mechanics for the glass core to calculate the crack propagation path and corresponding failure time. In addition, three factors including bending radius, tensile force and optical fiber diameter are investigated to find their impacts on the crack propagation process and failure time of the optical fiber under concerned situations. Finally, experiments are conducted and the results verify the correctness of the simulation calculation. It is believed that the proposed method could give a straightforward description of the crack propagation path in the inner glass core. Additionally, the predicted crack propagation time of the optical fiber with different factors can provide effective suggestions for improving the long-term usage of optical fibers.

Multiscale modeling for long-term life prediction of CFRP structures under cyclic loading

Long-term life prediction of carbon fiber reinforced polymers (CFRP) structures under cyclic loading is performed by multiscale modeling as the combination of fiber scale, layer scale, and structure scale. The concept of failure index for fiber and matrix based on the micromechanics of failure theory (MMF) developed by Sung-Kyu Ha is introduced for the determination of the failure corner in structure, failure layer in laminates, and failure mode of fiber or matrix. The accelerated testing methodology (ATM) developed by the authors is used for long-term life prediction of CFRP structures. An MMF/ATM method combined with MMF and ATM is applied to the long-term life prediction of open hole compressive CFRP laminates under cyclic loading as well as static loading. Then the predicted results are compared with the experimental ones. Results clarified that MMF/ATM method is useful for the long-term life prediction of CFRP structures under static and cyclic loading because the results mutually agree well.

Flexural performance of spliced beam connected and reinforced with self-tapping wood screws

Splicing method of bending elements is important for the restoration of ancient timber structures due to the principle of preserving as much as possible the original material. This study investigates the flexural performance of spliced beams connected and reinforced with self-tapping wood screws. An experimental program based on four-point bending test configuration was conducted to examine the strength, stiffness and ductility of spliced beams. The test results showed that the spliced beams’ average ultimate bending capacity reached 59.5% of the size and load duration adjusted specified bending capacity of the intact beam. Their stiffness achieved 64.3% of the specified design value in Canadian Wood Design Manual. The spliced beams experienced head pull-through failure of the self-tapping screws. This failure mode led to ductile behavior different from the typical tension failure mode of the wood fibers in glulam beam. Based on the experimental results, an analytical model that addressed the specific head pull-through failure mode was proposed to predict the flexural capacity of spliced beams. The analytical model was calibrated by the data of the head pull-through resistance test results and verified by full-size tests. Comparisons of the analytical and the test results reveal that the model can adequately predict the moment capacity of the spliced beams with the corresponding specific failure mode.

Some modifications of Hashin’s failure criteria for unidirectional composite materials

Failure criteria for unidirectional composite materials based on Hashin’s theory are developed. Although Hashin’s criteria are very popular in composite structural applications due to their simplicity of concept and ease of use, they do not always fit experimental results well. In the present study, the fundamental hypotheses proposed by Hashin are re-examined and re-evaluated. Hashin’s criteria for the tensile fiber mode and tensile matrix mode are modified based on physical considerations. The interaction between the fiber and matrix failure modes is also taken into account. Experimental verification for different kinds of unidirectional composites under various stress states demonstrates that the proposed failure criteria have good improvements over Hashin’s criteria, especially in the tensile fiber and matrix mode region. The present theory is in good agreement with physical reality and has a wide range of applicability.

Fatigue-induced in-situ strength deterioration of micro-polyvinyl alcohol (PVA) fiber in cement matrix

For soft fiber and brittle matrix system such as polymeric fiber-reinforced cementitious composites, the fiber strength deterioration dominates the performance of composites subject to fatigue loading. The fatigue-induced in-situ fiber strength deterioration in brittle matrix, however, has rarely been studied. In this paper, fatigue-induced in-situ strength deterioration of micro-polyvinyl alcohol (PVA) fiber in cement matrix was experimentally investigated. The effects of fiber embedment, fiber inclination, and fiber surface treatment on the in-situ strength of micro-PVA fibers are reported. The results show that fiber embedment into cement matrix not only reduces the in-situ strength of fiber but also changes the fatigue stress-cycle (S-N) curve and failure mode of fiber. Fiber inclination further decreases the in-situ strength of embedded fiber due to local stress concentration of bent fibers. Oil-treatment on fiber surface can effectively delay fatigue-induced in-situ strength deterioration of micro-PVA fiber.

A novel aircraft energy absorption strut system with corrugated composite plate to improve crashworthiness

ABSTRACTA novel crashworthy aircraft strut system with corrugated composite plate and hinge joints is proposed and investigated. The hinge joints could transfer axial impact load to the corrugated composite plate (CCP). The best crashworthy CCP is guaranteed to enhance the energy absorption ability. To verify the impact dynamic performance, the progressive failure model is adopted. Both of the fibre and matrix failure modes are considered in the failure criterion. To give a better failure behaviour, the single shell and stacked shell approaches are researched and compared. Based on the validated model, the sensitivities of layer number, layer angle and cross-sectional size are given. Numerical results show that the proposed crashworthy fuselage structure could enhance the energy absorption ability. The intra-laminar and delinamination could be simulated by the stacked shell model. A similar energy absorption ability is demonstrated for the different CCPs with progressive failure behaviour. An unstable failure behaviour may be exhibited if the lateral stiffness and strength is not enough to support the impact process.

Study on Performance of Steel Fiber Concrete Bridge Pier Specimens under Horizontal Cyclic Loading

Because of that steel fiber can effectively prevent the extension and development of small cracks in the concrete, steel fiber reinforced concrete has good toughness and tensile strength. In the application of building materials, steel fiber reinforced concrete is an ideal elastic-plastic material. For the seismic performance, it has advantages. In order to analyze the seismic performance of steel fiber reinforced concrete, 4 piers of the scale model test under horizontal cyclic loading were done. The results showed that failure mode of steel fiber reinforced concrete is better than that of ordinary concrete, and has a large yield moment under the external loads.

Fracture strength of CAD/CAM fabricated lithium disilicate and resin nano ceramic restorations used for endodontically treated teeth.

The purpose of the present study was to evaluate and compare the fracture strength and failure modes of endocrowns, zirconia post, and fiber post supported restorations and predict the clinical outcomes of six different prostheses used for endodontically treated teeth. Sixty (n=10) maxillary central incisors were restored with zirconia post/resin-nano-ceramic crown (ZrRNC), fiber post/resinnano-ceramic crown (FbRNC), zirconia post/lithium disilicate ceramic crown (ZrLDS), fiber post/lithium disilicate ceramic crown (FbLDS), resin-nano-ceramic endocrown (EndoRNC), and lithium disilicate ceramic endocrown (EndoLDS). Fracture strength test was performed. Fracture loads and modes were determined. The EndoLDS group had the highest fracture strength, followed by ZrRNC and EndoRNC group. However the results were not significantly different among groups (p>0.05). The failure modes of the restorations changed according to the restorative materials. Endodontically treated anterior teeth might be restored with endocrowns as well as other post-core restorations, however tooth fracture failures should be considered that affect reliability of endocrowns.