Junction Properties Interpretation of Textile Geogrids Using Multi-Junction Clamp

In this paper, multi-junction clamp was used for junction strength evaluation under 20, 50 and 100 mm/min of strain rate at ambient condition. One~eight rib specimens were gripped in the clamps and each gage length was 50 mm, 100 mm and 150 mm, respectively. Warp knitted and woven type geogrids were used to compare the effects of multi-junction clamping on junction and tensile strength, respectively. The results indicate that junction strength decreased while the number of junctions increased. When the strain rate was increased, junction strength of woven type increased, but there was no effect of strain rate on warp knitted type. The newly designed clamp test for geogrid junction strength in this research is more accurate than the single-junction test, considering the scale effect of specimens.

Experimental and numerical study of multi-scale tensile behaviors of Kevlar® 49 fabric

Kevlar® 49 fabrics have excellent performances such as high elastic modulus and high impact resistance, which are widely used in ballistic systems, aerospace, fabric reinforced composite materials and other fields. The present work studied the multi-scale mechanical behaviors of Kevlar® 49 in the forms of fiber, yarn and fabric subjected to uniaxial tension. The experimental results showed that the material mechanical properties are dependent on structural size scale and gage length of samples. The tensile strengths decrease with increasing gage length and structural size scale from fiber to yarn, and to fabric, and follow Weibull distribution by conducting statistical analysis, which is used to quantify the degree of variability in the tensile strengths of fiber and yarn with different gage lengths. At last, user-defined subroutines (UMAT) in ANSYS were implemented to simulate the tensile behaviors of single yarn and fabric by using the constitutive models of fiber and yarn, respectively, which considered their Weibull distribution in tensile strength. This probabilistic approach can simulate the multi-scale tensile behaviors of Kevlar® 49 accurately and reveal the mechanisms of deformation and failure process based on the various size scales. This approach is also applicable to study the multi-scale behaviors of other fabrics once their properties and Weibull parameters are determined.

The effects of gage length and strain rate on tensile behavior of Kevlar® 29 single filament and yarn

The mechanical properties of Kevlar® 29 single filaments and yarns with different gage lengths were investigated by utilizing an MTI miniature tester and an MTS load frame. Single yarns of 25 mm were also tested over four different strain rates using a drop-weight impact system. The experimental results showed that the mechanical properties of Kevlar® 29 are sensitive to gage length, structural size scale, and strain rate. The tensile strength decreased with increasing gage length and the structural scale from fiber to yarn, and increased with increasing strain rate. Weibull analysis was conducted to quantify the degree of variability in tensile strength. The obtained Weibull parameters were then used in an analytical model to simulate the stress–strain response of single yarn. Finally, Weibull parameters of single filaments with other gage lengths and strain rates were also obtained by fitting the stress–strain curves of single yarns with corresponding testing conditions.

Tensile and Statistical Analysis of Sisal Fibers for Natural Fiber Composite Manufacture

To achieve sustainability in the composite industry, natural fibers must be able to replace synthetic fibers .In this work the tensile properties of sisal fibers were determined. The relationships between tensile strength, young modulus, failure to strain and gage length was studied. Also variation in tensile strength was quantified using statistical analysis. The relationship between Weibull statistics and gage length were also investigated. The strength of the sisal fiber obtained in this work was between 255-377 MPA and decreased with an increase in gage length. The Weibull modulus obtained was similar for all gage lengths and was around 2.5.

Design of a Continuous-Bending-Under-Tension Machine and Initial Experiments on Al-6022-T4

An experimental technique called Continuous-Bending-Under-Tension (CBT) can produce elongations over two times that of a standard tensile test by preventing the necking instability from occurring. This is achieved by superposing plastic bending on tension along the gage length of the material using three rollers. The specimen is kept under tension as the rollers apply the three point bending and cyclically transverse along the gage length. This localizes the plastic deformation by subjecting the specimen to bending-under-tension. Details on the design of the unique CBT machine and some preliminary results for the CBT research being conducted are presented here. These results include CBT tests where the roller depth was varied to demonstrate the increased elongation compared to the traditional tension test, CBT repeatability, and a modified friction test using the CBT machine.

Kilometer-Long Optical Fiber Sensor for Real-Time Railroad Infrastructure Monitoring to Ensure Safe Train Operation

This study is aimed to develop a real-time safety monitoring of kilometer-long joint rails using a distributed fiber optic sensor. The sensor measures the distribution of Brillouin frequency shift along its length with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). The measurement distance and spatial resolution can be up to 25 km and 2 cm, respectively. The fiber optic sensor was first characterized and calibrated for distributed strain and temperature measurement, and then instrumented on a small-scale joint rail-like specimen in laboratory. The specimen was loaded at room temperature, and its strain distribution along the sensor was measured using a Neubrescope with high accuracy and spatial resolution. Given a gage length, the joint open change was determined and visibly identified from the measured strain distribution. Finally, an implementation plan of distributed sensors on a railway is introduced, including sensor deployment, sensor repair when broken, and cost analysis. The gage length at a crack is an important parameter in sensor deployment and investigated using finite element analysis. The results indicate that the distributed sensor can be used successfully to monitor the strain and temperature distributions in joint rails.

Interfacial Properties of Carbon Fiber Reinforced Thermoplastic and Thermosetting Composites

Carbon fiber composites are getting more and more widely used in aeronautics and astronautics, vessels, blades of wind turbine generators and so on. In this study, carbon fabric as reinforcement and thermoplastic and thermosetting resin as matrix were used to manufacture carbon fiber prepreg to mold the unidirectional carbon fiber sheet composite (Carbon/PA6 and Carbon/Epoxy). Specially, the multi-tensile tests of 90 degree carbon fiber sheet composite specimens with 150 mm gage length were carried out. After the 1st trial, the longer part of the fracture specimen was chosen as the experimental specimen of 2nd trial tensile test. Similarly, the 3rd trial was investigated. The mechanical properties of 90 specimens including tensile strength, elastic modulus and ultimate stain of polished specimens were investigated in the primary research. Then, the effect of trial on the mechanical properties, the comparison of failure probability distribution of ultimate strain of trials, the relation between gage length and tensile strength, tensile strength and ultimate strain were discussed according to the multi-tensile test result of each specimen. Additionally, the interfacial properties were discussed based on the SEM observation on the fracture surface.