Effect of Core Architecture on Charpy Impact and Compression Properties of Tufted Sandwich Structural Composites

This study presents a novel sandwich structure that replaces the polypropylene (PP) foam core with a carbon fiber non-woven material in the tufting process and the liquid resin infusion (LRI) process. An experimental investigation was conducted into the flatwise compression properties and Charpy impact resistance of sandwich composites. The obtained results validate an enhancement to the mechanical properties due to the non-woven core and tufting yarns. Compared to samples with a pure foam core and samples without tufting threads, the compressive strength increased by 45% and 86%, respectively. The sample with a non-woven layer and tufting yarns had the highest Charpy absorbed energy (23.85 Kj/m2), which is approximately 66% higher than the samples without a non-woven layer and 90% higher than the samples without tufting yarns. Due to the buckling of the resin cylinders in the Z-direction that occurred in all of the different sandwich samples during the compression test, the classical buckling theory was adopted to analyze the differences between the results. The specific properties of the weight gains are discussed in this paper. The results show that the core layers have a negative effect on impact resistance. Nevertheless, the addition of tufting yarns presents an obvious benefit to all of the specific properties.

Effects of Mo segregation on Charpy absorbed energy in Ti-12Mo alloys

Beta phase stabilizing elements such as Mo have strong tendency to segregate. We have introduced swirly type segregation of Mo in Ti-12Mo (mass %) alloy through groove bar rolling. After solution treatment and low temperature aging, hard omega phase was precipitated heterogeneously, which improved the room temperature tensile elongation values without sacrificing tensile strength. In this study, the effect of Mo segregation and heterogeneous distribution of omega phase on Charpy absorbed energy was investigated in Ti-12Mo alloy. Samples with two types of segregation were prepared; namely, swirly segregation in bar rolled sample and layered segregation in plate rolled sample. For comparison, we have also prepared Ti-12Mo bar samples with lesser Mo segregation, through high temperature thermomechanical treatment. Charpy impact tests were carried out at room temperature, 373 K and 473 K, respectively, using the samples after aging to introduce isothermal omega-phase. The samples with the segregation exhibited higher Charpy absorbed energy, especially at higher temperature of 473 K, while the sample with the swirly segregation showed higher Charpy absorbed energy than that with the layered segregation. The sample with lesser Mo segregation exhibited brittle intergranular fracture surface after Charpy testing. On the contrary, samples with Mo segregation exhibited ductile transgranular fracture surfaces.

Effect of Precipitation State on Strength and Toughness of Precipitation Hardened Hot Rolled Steel Sheet

In this work, to clarify the effect of carbide precipitation state on strength and toughness, Ti,V alloyed precipitation hardened ferrite single phase steel sheets with different carbide size were investigated. In order to change the precipitated particle size, cooling conditions after hot rolling were changed. Under condition A, steel sheets were cooled to 873K by water spray (for fine precipitation). Under condition B, steel sheets were air-cooled from 1053K for 20sec, then cooled by water spray to 873K (for coarse precipitation). The experimental results were following. The balance of tensile strength and Charpy absorbed energy was better in condition B. (Ti,V)C were observed in both conditions, but the size of (Ti,V)C were larger in condition B. From the above, it was suggested that as the carbide size become larger, the decrease in toughness per strengthening amount becomes smaller.

Verification of Applicability of Battelle Two-Curve Method to Ultrahigh-Pressure Rich-Gas Pipelines Based on a Full-Scale Burst Test

A full-scale gas burst test was conducted to confirm the behavior of unstable ductile crack propagation and arrest and to confirm the required toughness value to prevent unstable ductile fracture under an ultrahigh pressure of 18 MPa. A full-scale test was conducted at the Spadeadam test site in the UK for unburied pipes. The test pipes used in this test were of API 5L Grade L450 with outer diameter of 610 mm and thickness of 17.5 mm. The toughness of the test pipes increased away from the center, where an explosive charge was placed across the top of the girth weld for crack initiation. The gas used in the test consisted of ∼89% methane and other heavy hydrocarbon gas components, and the test temperature was 0 °C. A gas circulation loop was constructed to ensure that a homogeneous gas mixture and temperature were achieved throughout the test rig. In addition to dynamically measuring the ductile crack velocity and decompression behavior of the rich gas, as has often been done in previous burst tests, the circumferential distribution of the decompression behavior was measured using circumferentially placed pressure transducers. Furthermore, the fracture strain near the propagating crack was measured. The initiated unstable ductile crack was arrested in the third pipe. From the material properties of the test pipes in which the unstable ductile crack was arrested, the required Charpy absorbed energy and DWTT absorbed energy to prevent unstable ductile fracture in unburied pipes were obtained. In addition, the above data can be useful for validating numerical models that evaluate the propagation/arrest of unstable ductile fracture. The required Charpy and DWTT absorbed energy values obtained in this test were compared with those predicted by the Battelle Two-Curve Method (BTCM). As noted in previous studies, it was confirmed that the BTCM underestimates the required Charpy absorbed energy and requires a certain correction factor for precise evaluation, whereas the DWTT absorbed energy predicted by BTCM was consistent with the experimental result.

Effect of Charpy Striker Configuration on Low- and High-Energy NIST Verification Specimens

Charpy machines can be equipped with strikers having two different configurations, corresponding to an edge radius of 2 mm or 8 mm. Both striker types are covered by ASTM E23 and ISO 148-1. The effect of striker type on Charpy absorbed energy has been extensively investigated in the past, and clear evidence has been published showing that when using 8 mm strikers, absorbed energy (KV) tends to increase for specimens with KV ≥ 200 J. In this paper, we investigate how striking edge radius affects certified values and uncertainties for National Institute of Standards and Technology (NIST) low-energy and high-energy verification specimens. Test data from two low-energy and two high-energy Charpy lots, analyzed in a statistically rigorous manner, were somewhat contradictory and led to the decision to separately certify low-energy and high-energy lots for use with 2 mm and 8 mm strikers. This agrees with previous findings by other NIST researchers, who recommended individual certifications for the two strikers at all energy levels.