Transverse Tensile Research Articles

Time-varying deterioration of bamboo mechanical properties

Bamboo is a type of fast-growing and renewable natural resource that is an ideal building material. In this study, the longitudinal tensile, longitudinal compressive, flexural, longitudinal shear, transverse tensile, and transverse compressive stress-strain and strength properties of bamboo with a period of 240 days were conducted to study the time-varying deterioration performance of bamboo. The results showed that the mechanical properties of bamboo decreased gradually with the passage of time. The transverse compressive strength deteriorated the most, and the longitudinal tensile strength deteriorated the least. After 240 days of tests, bamboo CCS decreased by 52.5% and UTS decreased by 25.4%. Formulas to predict deterioration of mechanical properties were put forward and validated. It was found that the nodes of bamboo influenced its mechanical properties. The deterioration degree of the test specimens with nodes was slightly higher than that of the test specimens without nodes. These findings provide evidence about the deterioration mechanism of bamboo and are significant for promoting the development of bamboo architecture.

Laser-assisted automated tape laying: Effects of placement rate and heated tooling on layer bonding and tensile properties

This paper investigates the processing parameters placement rate and tooling temperature of laser-assisted automated tape laying (ATL). Plates with carbon fiber-reinforced polyether ether ketone (CF/PEEK) were produced at 6 m/min, 9 m/min and 18 m/min, and 23°C and 250°C tooling temperature, respectively. Correlations of processing conditions with micrographs, void content, thickness, the degree of crystallinity and the shear strength of the compression shear test, including a fractographic analysis, were derived. Processing conditions that increase the degree of crystallinity were only found to improve the compression shear strength at 6 m/min placement rates, primarily due to a void content below 3.4 % and degree of crystallinity above 26 %. The fractographic analysis derived from the compression shear test revealed a strong correlation between the degree of crystallinity and the size of ductile drawings. In contrast, the transverse tensile test showed no influences on the ATL processing conditions, whereas the tensile strength in fiber direction decreased by 11 % from a placement rate of 6 m/min to 18 m/min. ATL with a 250°C tooling temperature increased the strengths by 14 % compared to those at room temperature. A further tensile strength improvement of 0° and 90° to 1754 MPa and 75 MPa was obtained by a subsequent out-of-autoclave consolidation using vacuum bagging.

Investigating the role of fibre-matrix interfacial degradation on the ageing process of carbon fibre-reinforced polymer under hydrothermal conditions

The aqueous environment can deteriorate the fibre-matrix interface of carbon fibre-reinforced polymer (CFRP), significantly impairing the non-fibre-dominated mechanical properties. Thus, this study aimed to quantitatively analyse the impact of interfacial degradation on the hydrothermal ageing mechanism and process of the CFRP. Firstly, entire water absorption process of the CFRP under hydrothermal conditions was divided into three stages according to experimental measurement of its water content. Based on this division of stages, a novel water diffusion model was established for the hydrothermally aged CFRP. To measure the mechanical degradation, tensile tests were conducted on unaged, aged, and redried neat epoxy and transversely positioned unidirectional (UD) CFRP specimens. It was found that the transverse tensile strength degradation of UD CFRP was irreversible due to the permanent interfacial debonding between the fibres and matrix, in contrast to the reversible ageing of the epoxy matrix. To further quantify the fibre-matrix interfacial ageing, physically-based models were established for the degraded interfacial strength of CFRP subjected to hydrothermal conditions. After the characterization of the modelling coefficients, the physically-based models can be employed to predict interfacial strength inside the aged CFRP for various ageing durations. The prediction error was only 4.57% for the transverse tensile strength of degraded UD CFRP with various ageing durations from the representative volume element (RVE) simulation with its interfacial strength provided by the physically-based models, validating the effectiveness of the proposed physically-based models for degraded fibre-matrix interface under various ageing conditions.

An Insight into the Mechanical Properties of Unidirectional C/C Composites Considering the Effect of Pore Microstructures via Numerical Calculation.

Pores are common defects generated during fabrication, which restrict the application of carbon/carbon (C/C) composites. To quantitatively understand the effects of pores on mechanical strength, this paper proposes a representative volume element model of unidirectional (UD) C/C composites based on the finite element method. The Hashin criterion and exponential degraded rule are used as the failure initiation and evolution of pyrolytic carbon matrices, respectively. Interfacial zones are characterized using the cohesive constitutive. At the same time, periodic boundary conditions are employed to study transverse tensile, compressive, and shear deformations of UD C/C composites. Predicted results are compared with the experimental results, which shows that the proposed model can effectively simulate the transverse mechanical behaviors of UD C/C composites. Based on this model, the effects of microstructural parameters including porosity, pore locations, the distance between two pores, pore clustering, and pore shapes on the mechanical strength are investigated. The results show that porosity markedly reduces the strength as porosity increases. When the porosity increases from 4.59% to 12.5%, the transverse tensile, compressive, and shear strengths decrease by 35.91%, 37.52%, and 30.76%, respectively. Pore locations, the distance between two pores, and pore clustering have little effect on the shear strength of UD C/C composites. For pore shapes, irregular pores more easily lead to stress concentration and matrix failure, which greatly depresses the bearing capacity of UD C/C composites.

Revisiting the sequential evolution of sizing agents in CFRP manufacturing to guide cross-scale synergistic optimization of interphase gradient and infiltration

Using sizing agents instead of various nanoparticles to modify carbon fibers is widely recognized as the most practical approach to address processing issues and improve interfacial properties in carbon fiber reinforced polymer composites. However, a limited understanding of sizing agent evolution during composite manufacturing hinders comprehensive theoretical guidance for sizing treatment, thereby limiting further enhancement of composite performance. Here we disentangled the sizing agents into chemical anchoring and physical adsorption components, and elucidated the sequential wetting, diffusion, and crosslinking evolution processes of sizing agents across scales. By manipulating the proportion of chemical anchoring and physical adsorption in the sizing agents, the interfacial modulus gradient and infiltration efficiency were synergistically optimized. Consequently, significant improvements of 26.2 % in interfacial shear strength (IFSS) and 52.9 % in transverse fiber bundle tensile (TFBT) strength were achieved, indicating enhanced interfacial stress transfer and reduced internal defects in the composites. In summary, this work revisited the cross-scale evolution and mechanism of sizing agents during composite manufacturing, and thus provided a new paradigm for optimizing composite performance.

Constructing Mechanochromic Fluorescent Interphase via Core-Shell Microcapsules: A Route for Interface Reinforcing and Damage Self-Reporting of CFRP Composites.

Perylenediimide-chitosan/γ-poly (glutamic acid) microcapsules sizing (PDI-CS/γ-PGA) core-shell microcapsule is designed and used to establish a novel interphase in carbon fiber/epoxy (CF/EP) composite, and the interfacial property, as well as the damage self-reporting of the composite, is compared with desized carbon fiber (CF-desized)/EP and commercial carbon fiber (CF-COM)/EP composite. The ruptured PDI-CS/γ-PGA microcapsule exhibits strong "turn-on" green fluorescence from the released PDI upon mechanical stimuli. The anchoring of PDI-CS/γ-PGA microcapsule on carbon fiber with PDI-CS/γ-PGA microcapsules sizing (CF@PDI-CS/γ-PGA) surface results in increased chemical activity and roughness, exhibiting a weak green fluorescence signal instead of non-fluorescence on CF-desized and CF-COM surface. The transverse fiber bundle tensile (TFBT) strength of CF@PDI-CS/γ-PGA composite is 80.97% and 31.09% higher than those of CF-desized/EP and CF-COM/EP composite, which is attributed to the mechanical interlocking and chemical bonding interaction between carbon fiber and epoxy matrix by introducing PDI-CS/γ-PGA microcapsule with spherular structure and active groups. After microdroplet testing, the strong "turn-on" green fluorescence signal of the released PDI from the microcapsules is detected in the interfacial debonding regions, realizing the microscopic damage self-reporting of CF@PDI-CS/γ-PGA composite.

Effects of Longitudinal Alternating Magnetic Field on the Microstructure and Properties of CMT-WAAM Al-5%Mg Alloy

The major challenges in wire arc additive manufacturing (WAAM) of aluminum alloys include improving the forming quality, reducing pore and crack defects, and optimizing the overall mechanical properties. In this study, an external longitudinal alternating magnetic field (LAMF) was applied to assist cold metal transfer (CMT) WAAM process of Al-5%Mg alloy. This study compared the effects of different LAMF intensity parameters on the electrical behavior, molten droplet transition, macroscopic forming, microstructure and mechanical properties of CMT-WAAM multi-layer thin-walled structures. Compared with the situation without the alternating magnetic field, the application of an external LAMF could cause the arc to expand and rotate, deflect droplets and stir the molten pool periodically. When the alternating magnetic field parameters were set at a current of 3A and frequency of 100Hz with magnetic field intensity of 9mT, the deposited samples achieved macroscopic forming with superior surface quality and geometric accuracy, and the internal defect rate was reduced from 0.742% to 0.168%. Also, the mean grain size of the deposited layer was reduced from 186μm to 154μm, and the average hardness was increased from 68.1HV0.2 to 91.1HV0.2 with an improvement rate of 33.7%. Moreover, the longitudinal tensile strength was increased from 249 MPa to 257 MPa, the transverse tensile strength was increased from 264 MPa to 273 MPa, and the yield strength and elongation at break were both increased. This study demonstrates theoretical guidance for enhancing the component overall performance of aluminum alloy LAMF-WAAM technology.

Experimental analysis of the forming behavior of uni- and bidirectional non-crimp fabrics for different geometries

For efficient large-series production and improved process design, a profound understanding of a textile’s forming behavior is crucial to ensure adequate drapability and defect-free components. Woven fabrics have often been the focus of research due to their easier formability, while non-crimp fabrics (NCFs) have been investigated much less despite their higher lightweight potential, resulting in a limited experimental basis for the validation of numerical models. Therefore, forming experiments of a unidirectional and a bidirectional NCF are conducted for different configurations and punch shapes, including hemisphere, tetrahedron, and square box. The macroscopic strains are captured throughout the entire process using digital image correlation (DIC) and comprehensively analyzed in combination with the outer contour and resulting defects. Fundamental differences in the deformation behavior of both textiles are identified. For the balanced Biax-NCF, the tricot stitching couples the deformation of both fiber layers and the fabric mainly deforms under symmetrical shear with limited yarn slippage or defects. For the highly unbalanced UD-NCF, the lack of a second fiber direction results in an asymmetrical deformation behavior. The UD-NCF deforms due to shear parallel to the fiber yarns superimposed with transverse tensile and compressive strains in different deformation modes. The data generated in this study is freely available at https://doi.org/10.5281/zenodo.12516897.

Synthesis and characteristics of natural fiber reinforced nano hybrid composite – an experimental study

Abstract Recently, research on natural hybrid composites has occupied a significant role in the materials science sector. Due to the low density, high specific strength, dimensional stability, and biodegradability, natural fiber composite has become a predominant research area. The present study deals with the fabrication of a jute–banana fiber hybrid composite using the hand layup method with compression molding. A fixed concentration of 5 % carbon nanotubes (CNT) is included over the fiber surfaces as an additional reinforcement material to improve their thermal and electrical conduction properties. The prepared composite material is subjected to different fiber loading (0, 10, 20, and 30 wt.%) with jute and banana weight ratios of 1:1, 1:3, and 3:1. The investigation is conducted for testing the physical, mechanical, and thermal properties of the prepared composites along with morphological studies. Final results revealed a maximum longitudinal tensile strength of 68.8 MPa, 67.0 MPa, and 86.7 MPa and the maximum transverse tensile strength of 41.2 MPa, 40.5 MPa, and 48.0 MPa at 30 wt.% with respective fiber ratio of 1:1, 1:3, and 3:1. The maximum longitudinal flexural strength of this hybrid composite is noticed as 94 MPa, 90 MPa, and 103 MPa for the weight ratio of 1:1, 1:3, and 3:1. Higher impact energy is obtained for the composition ratio of 1:3 (JBC 1:3) which has more banana fiber than the other two. A new attempt at adding carbon nanotubes has improved their thermal conductivity compared to regular composites of jute–banana.

Study of the effect of void defects on the mechanical properties of fiber reinforced composites

This study is to investigate the mechanical properties of fiber-reinforced polymer (FRP) composites considering void defects by adopting a representative volume element model. The results reveal that initial damage always sprouts at the interface, the void defects affect the location of the initial damage and are the dominant factor in determining the stress required for damage sprouting. In addition, the void defects as well as the neighboring debonding interfaces together determine the direction of the main damage evolution zone. The transverse tensile properties are most affected by the void defects, while the longitudinal tensile properties are least affected. In particular, the strength is more sensitive to void defects than that of elastic constants. In addition, the mechanical properties of high Fiber Volume Fraction (FVF) FRP composites are significantly stronger affected by void defects than those of low FVF FRP composites.

Anisotropy of microstructure features and tensile properties of Ti–48Al–2Cr–2Nb alloy produced by electron beam powder bed fusion

A Ti–48Al–2Cr–2Nb alloy was produced by electron beam powder bed fusion. The effect of the volume energy density parameter on the forming quality was investigated, and the tissue characteristics, hardness distribution, and mechanical properties of the alloy were analyzed. The results showed that the quality was better when the volume energy density parameter was 21.5–22.5 J/mm3. The microstructure of the alloy has the phenomenon of changing with the forming height: with an increase in the forming height, the forming part produces the phenomenon of strip microstructure along the construction direction, and the regional microstructure variability occurs under the cross section of the same height. The average hardness of the alloy reached 375.2 HV at the bottom, 381.8 HV in the middle, and 389.6 HV at the top, and the standard errors of the hardness values were 12.40, 10.49, and 7.12 HV, respectively, with the microhardness showing a gradual increase along the molding direction, and the homogeneity was gradually better. The transverse tensile strength at room temperature reached 526 MPa, the yield strength reached 461 MPa, and the elongation at break reached 1.24%, while the longitudinal tensile strength reached 486 MPa, the yield strength reached 414 MPa, and the elongation at break reached 1.02%.

Interfacial property enhancement of carbon fiber/epoxy composites via constructing a gradual modulus interphase with a waterborne bio‐based spiro diacetal epoxy emulsion

AbstractIn this article, to explore the utilization of bio‐based epoxy resin in the preparation of sizing agents for carbon fibers (CFs), a bio‐based epoxy emulsion (S‐P‐S) derived from spiro diacetal epoxy (SDE) resin was prepared and compared to the traditional diglycidyl ether of bisphenol A (DGEBA) based emulsion (D‐P‐D) and a mixed emulsion of S‐P‐S and D‐P‐D (S‐P‐S&D‐P‐D). The CF sized with S‐P‐S (CF‐(S‐P‐S)) showed improved surface oxygen content (22.86%) and roughness (40.9 nm), enhancing wettability and interfacial bonding between the fiber and the matrix. Nanoindentation test and AFM results showed the enhanced interfacial stiffness and a gradual modulus interphase with a thickness of 381 nm in CF‐(S‐P‐S) reinforced epoxy resin composite (CF‐(S‐P‐S)/EP). Therefore, the resulting CF‐(S‐P‐S)/EP composite possesses the best mechanical properties, with the transverse fiber bundle tensile (TFBT) strength of 27.3 ± 1.45 MPa and the interfacial shear strength (IFSS) of 85.6 ± 8.26 MPa. These results highlight the potential of the SDE‐based emulsion (S‐P‐S) to enhance the interfacial properties and mechanical performance of CF/EP composite, offering a sustainable alternative to conventional petroleum‐based epoxy resins.Highlights Emulsion (S‐P‐S) was prepared using spiro diacetal epoxy (SDE) for carbon fiber sizing. Properties of S‐P‐S sized CF (CF‐(S‐P‐S)) and its composite were evaluated. Spiro diacetal structure created a gradual modulus interphase in CF‐(S‐P‐S)/EP. The interfacial properties of the CF‐(S‐P‐S)/EP composite were greatly improved. Bio‐based SDE resin showed promise for optimizing carbon fiber composite interphase.

Flux enhancement with titanium or vanadium oxides addition for superior submerged arc welding of HSLA steel plates

A high-strength low-alloy (HSLA) steel plate of 10 mm thickness underwent submerged arc welding with enhanced fluxes containing additional titanium oxide (TiO2) or vanadium oxide (V2O5). The addition of TiO2 led to the development of a finer acicular ferrite structure but coarsening the carbide and martensite/austenite (M/A) constituents, which marginally improved the hardness, tensile strength, and ductility of weld metal. Conversely, incorporating V2O5 facilitated a substantial vanadium absorption (0.7 wt. %) in the weld metal, giving rise to a distinctive acicular microstructure less reliant on ferrite nucleation at non-metallic inclusions than conventional acicular ferrite. The distinctive microstructure, unique to vanadium steels, combined lath bainite with irregularly shaped granular bainite. The resultant dual-mode bainitic structure, coupled with a more uniform distribution of refined microphase constituents, outperformed the conventional acicular ferrite, delivering more than 20% and 13% improvements in yield and tensile strengths respectively, as evidenced by transverse tensile tests on the weld metals.

Influence of CMT welding parameters on microstructural and properties investigation of dissimilar weld joint for aluminum bronze and carbon steel

Cold Metal Transfer (CMT) welding technology has improved the appearance of weld beads and revolutionized the welding of thicker materials and dissimilar metals with precise metal deposition and reduced heat input. Cold Metal Transfer welding is predominantly used in a variety of industry applications, including aerospace, shipbuilding, automotive and marine industries. In this study, aluminum bronzes and carbon steel were joined by using CMT welding, a variant of the Gas Metal Arc Welding process, with ERCuAl-A2 as the filler metal. Optical microscopy was used to examine the microstructure of the CMT weld joint between aluminum bronze and carbon steel. Results have indicated that dissimilar metals such as aluminum bronze, and carbon steel could be successfully joined by CMT under various processing parameters. The tensile and bending strengths of the dissimilar joint were 490 MPa and 822 MPa, respectively. A variety of intermetallic compounds and solid solutions were generated in the weld zone and fusion zone. The micro-hardness in the carbon steel side of the fusion zones increased sharply, which was 164 HV in the welded condition. The dissimilar joint was stronger than the carbon steel, as the ductile fracture occurred on the carbon steel during the transverse tensile test of the welded specimen. The microstructure interpretation of welded dissimilar joints was analyzed by scanning electron microscopy and transmission electron microscopy.

Process optimization of continuous aramid fiber reinforced PA12 filaments and printed composites

AbstractA multi‐stage fiber spreading process for the preparation of high‐performance continuous aramid fiber reinforced nylon 12 (CAF/PA12) composites was proposed in this paper. The effects of spreading rod crown radius, spreading rod axis height and traction speed on fiber impregnation effect and filaments properties were investigated. The fiber volume fraction of the prepared filament was approximately 30%. And the maximum tensile strength and modulus of the filaments were 839.89 MPa and 41.35 GPa, which were 34.36% and 34.30% higher than unspreading filaments, respectively. The influences of printing process parameters such as printing temperature, the combination of layer thickness and printing spacing on the transverse tensile properties of the specimens were studied. Printed specimens reached a transverse tensile strength and tensile modulus of 13.988 MPa and 1.293 GPa, respectively. The influences on low velocity impact properties of the specimens were also investigated in terms of impact energy and printing stacking sequences. Results revealed that the impact threshold energy of orthotropic ([0/90/0/90]2) specimens was 50 J. Quasi‐isotropic ([0/45/90/−45]2) specimens exhibited the superior impact resistance with an impact load of 4.939 kN. Macro‐ and micro‐matrix crack, surface buckling, fiber fracture and delamination were the main failure modes of the specimens.Highlights A novel thermoplastic composite filament forming process was proposed, and the filament forming equipment was designed and manufactured. Continuous aramid fiber‐reinforced PA12 filaments with about 30% fiber content were prepared by orthogonal tests under different forming process conditions, which showed maximum tensile properties of 839.89 MPa and 41.35 GPa, respectively. Spreading multiplication was positively related to filament tensile properties, which was major affected by the axial height of the spreading rod. Transverse tensile strength (13.988 MPa tensile strength and 1.293 GPa tensile modulus) of printed specimens was investigated under different printing parameters. Fiber orientation had a significant effect on the low‐velocity impact properties. Micro‐ and macro‐matrix crack, surface buckling, fiber fracture and delamination were the main failure modes of the low‐velocity impact specimens.

Outstanding interlaminar strength of carbon fiber reinforced epoxy resin via graphene oxide chemical bridge bonding

Carbon fiber reinforced polymers (CFRPs) are susceptible to interlaminar failure under high shear stress, which reduces their service life. Herein, we report a strategy to address the interlaminar damage problem of CFRPs by utilizing graphene oxide (GO) as a bridge to chemically bond carbon fibers and epoxy resin. Amino groups were grafted on the surface of carbon fibers to react with GO, then active amino functional groups were introduced onto GO, enabling crosslink with the epoxy resin. The chemical bonding force and mechanical interlocking effect of GO tightly integrated the carbon fibers with the epoxy resin, greatly reducing relative slip under high shear stress. This flexible and robust connection resulted in a significant improvement in the interfacial adhesion strength of CFRPs. The GO content and type of amino reactants were optimized to fabricate CFRPs, and the interlaminar shear strength and transverse fiber bundle tensile strength were increased to 76.36 MPa and 34.2 MPa, which were 46.2 % and 77.2 % higher than those of pre-modification materials, respectively. This research demonstrates that the chemical bonding provided by grafting graphene oxide significantly enhances interlaminar bond strength, thereby extending the service life of CFRPs and offering a promising path for manufacturing high-strength composites.

Hygroscopic damage of fiber–matrix interface in unidirectional composites: A computational approach

The mechanical properties of fiber-reinforced composites are significantly affected by hygroscopic exposure. Recent experimental findings reveal that the diffusion of water molecules results in void formation at the fiber–matrix interface, contributing to ∼1% increase in porosity. This paper presents a computational micromechanics framework to analyze the damage behavior of unidirectional composites under hygroscopic aging and transverse loads. First, a mathematical relation for the porosity evolution with moisture content in the composite is obtained. Leveraging this correlation, the aged composite is modeled as a porous microstructure consisting of fiber, matrix, and voids at the fiber–matrix interface in finite element simulations. The fiber is considered elastic, and the matrix is modeled as an elastoplastic material using a pressure-dependent yield model to capture tension–compression asymmetry. A cohesive interface is considered between the fiber and matrix. Simulation results indicate that a void at the interface significantly influences plastic strain evolution and stress distribution, leading to early damage initiation and reduced strength. Previous works have indicated that matrix and inter-fiber voids do not have a significant impact on the strength of composites when their combined porosity is below 1%. On the contrary, this study demonstrates that a porosity of as low as 0.1% at the fiber–matrix interface can result in an 11% decrease in the transverse tensile strength of the composite. A parametric study is conducted to understand the fundamental effects of pore size, location, and relative position on the transverse tension, compression, and shear loading responses of a unidirectional composite. For a given moisture content, the predicted strength of the hygroscopic aged composite exhibits a lower and upper bound. The strengths observed in the experiments fall within the model-predicted range. Additionally, a computational method is proposed that incorporates the effects of porosity at the fiber–matrix interface into a modified cohesive strength. This method allows efficient computations and failure predictions for water or moisture-aged strength degradation of unidirectional composites.

Bio-Inspired Helicoidal Composite Structure Featuring Graded Variable Ply Pitch under Transverse Tensile Loading

Biostructures found in nature exhibit remarkable strength, toughness, and damage resistance, achieved over millions of years. Observing nature closely might help develop laminates that resemble natural structures more closely, potentially improving strength and mimicking natural principles. Bio-inspired Carbon Fiber-Reinforced Polymers (CFRP) investigated thus far exhibit consistent pitch angles between layers, whereas natural structures display gradual variations in pitch angle rather than consistency. Therefore, this study explores helicoidal CFRP laminates, focusing on the Non-Linear Rotation Angle (NLRA) or gradual variation to enhance composite material performance. In addition, it compares the strength and failure mechanisms of the gradual configuration with conventional helicoidal and unidirectional (UD) laminates, serving as references while conducting transverse tensile tests (out-of-plane tensile). The findings highlight the potential of conventional and gradual helicoidal structures in reinforcing CFRP laminates, increasing the failure load compared to unidirectional CFRP laminate by about 5% and 17%, respectively. In addition, utilizing bio-inspired configurations has shown promising improvements in toughness compared to traditional unidirectional laminates, as evidenced by the increased displacement at failure. The numerical and experimental analyses revealed a shift in crack path when utilizing the bio-inspired helicoidal stacking sequence. Validated by experimental data, this alteration demonstrates longer and more intricate crack propagation, ultimately leading to increased transverse strength.

Micromechanical modeling of longitudinal compression behavior and failure mechanism of unidirectional carbon fiber reinforced aluminum composites involving initial fiber misalignment

AbstractA micromechanical model with realistic initial fiber misalignment (IFM) was developed to simulate the longitudinal compression behavior of unidirectional carbon fiber/aluminum composites. The matrix and fiber were modeled using ductile damage law and brittle fracture model, respectively. The interfacial properties were firstly determined by the single‐fiber push‐out and transverse tensile tests, and the cohesive zone model was adopted to capture the interfacial behavior. The calculated compressive response curve is in alignment with the experimental data. Compression failure can be attributed to fiber kinking, possibly triggered by the matrix shear damage. The increase of IFM angle makes the failure mode being transformed from fiber crushing to fiber kinking, along with a significant decrease in compressive strength. With the fiber content increasing, the compressive strength increases first and then decreases, while the compressive modulus increases monotonically. Increasing interfacial strength significantly improves the compressive strength, but this is limited by the matrix properties.

A matrix failure criterion independent of empirical parameters for brittle fiber-reinforced composites

Based on Hashin's fracture plane assumption, a matrix failure criterion for brittle fiber-reinforced composites is proposed. The failure function is expressed as a quadratic polynomial of the stress components on the fracture plane. The unknown coefficients in the failure criterion are only calibrated by the three basic strengths of unidirectional composites, i.e., the transverse tensile strength, transverse compressive strength, and longitudinal shear strength, thus overcoming the limitation of requiring empirical parameters in most previous matrix failure criteria. Especially, under plane stress states (σ22,τ21), an analytical solution for the fracture angle of unidirectional composites can be provided. The prediction results of the proposed criterion are consistent with a large number of experimental data, confirming its applicability. In addition, the study establishes the relationship among the three transverse basic strengths (Yt, Yc and S23). It can be used to predict S23 which is difficult to measure experimentally.