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21 pages, 7324 KiB

Open AccessArticle

Investigations on the Fatigue Behaviour of 3D-Printed Continuous Carbon Fibre-Reinforced Polymer Tension Straps

by Tadej Vidrih, Peter Winiger, Zafiris Triantafyllidis, Valentin Ott and Giovanni P. Terrasi

Polymers 2022, 14(20), 4258; https://doi.org/10.3390/polym14204258 - 11 Oct 2022

Cited by 4 | Viewed by 2610

The focus of this research is an investigation on the fatigue behaviour of unidirectional 3D-printed continuous carbon fibre-reinforced polymer (CFRP) tension straps with a polyamide matrix (PA12). Conventionally produced tension straps are becoming established components in the mechanical as well as the civil engineering sector, e.g., as rigging systems for sailing boats and cranes and—recently introduced—as network arch bridge hangers. All these structures are subjected to high fatigue loads, and although it is commonly reported that carbon fibre-reinforced polymers show excellent fatigue resistance, there is limited understanding of the behaviour of CFRP loop elements under such loads, especially in combination with fretting at the attachment points. Research on this topic was performed at Empa in the past decade on thermoset CFRP straps, but never before with 3D-printed continuous CFRP straps with a thermoplastic matrix. This paper examines an additive manufacturing and post-consolidation method for producing the straps and presents initial results on their fatigue performance, which show that the fatigue endurance limit of the investigated 3D-printed and post-consolidated CFRP strap design is acceptable, when compared to steel tendons. However, it is still 20% lower than conventionally produced CFRP straps using out-of-autoclave unidirectional carbon fibre prepregs. The reasons for these findings and potential future improvements are discussed. Full article

(This article belongs to the Special Issue Additive Manufacturing of Fiber-Reinforced Polymer Composites)

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20 pages, 59813 KiB

Open AccessArticle

Fretting Fatigue Performance of Unidirectional, Laminated Carbon Fibre Reinforced Polymer Straps at Elevated Service Temperature

by Danijela Stankovic, Luke A. Bisby, Zafiris Triantafyllidis and Giovanni P. Terrasi

Polymers 2021, 13(19), 3437; https://doi.org/10.3390/polym13193437 - 7 Oct 2021

Cited by 2 | Viewed by 3090

Abstract

The fretting fatigue performance of laminated, unidirectional (UD), pin-loaded, carbon fibre-reinforced polymer (CFRP) straps that can be used as bridge hanger cables was investigated at a sustained service temperature of 60 °C. The aim of this paper is to elucidate the influence of the slightly elevated service temperature on the tensile fatigue performance of CFRP straps. First, steady state thermal tests at ambient temperature and at 60 °C are presented, in order to establish the behaviour of the straps at these temperatures. These results indicated that the static tensile performance of the straps is not affected by the increase in temperature. Subsequently, nine upper stress levels (USLs) between 650 and 1400 MPa were chosen in order to establish the S–N curve at 60 °C (frequency 10 Hz; R = 0.1) and a comparison with an existing S–N curve at ambient temperature was made. In general, the straps fatigue limit was slightly decreased by temperature, up to 750 MPa USL, while, for the higher USLs, the straps performed slightly better as compared with the S–N curve at ambient temperature. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Advanced Polymers and Polymer Composites)

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14 pages, 19483 KiB

Open AccessArticle

Fatigue and Durability of Laminated Carbon Fibre Reinforced Polymer Straps for Bridge Suspenders

by Fabio Baschnagel, Rea Härdi, Zafiris Triantafyllidis, Urs Meier and Giovanni Pietro Terrasi

Polymers 2018, 10(2), 169; https://doi.org/10.3390/polym10020169 - 10 Feb 2018

Cited by 21 | Viewed by 6868

Abstract

Steel cables and suspenders in bridges are at high risk of corrosion-fatigue and in some cases of fretting-fatigue in their anchorages. These factors greatly limit the service stresses of a specific cable system and involve expensive protection measures. In order to investigate the above limitations, the fretting fatigue behaviour of pin-loaded carbon fibre reinforced polymer (CFRP) straps was studied as models for corrosion-resistant bridge suspenders. Two types of straps were tested: small model straps with a sacrificial CFRP ply and large full-scale straps. In a first phase, five fully laminated and carbon pin-loaded CFRP model straps were subjected to an ultimate tensile strength test. Thereafter, and in order to assess their durability, 20 model straps were subjected to a fretting fatigue test, which was successfully passed by 4 straps. An S-N curve was generated for a load ratio of 0.1 and a frequency of 10 Hz. In a second phase, one full-scale strap was tested for its ultimate tensile strength and two full-scale straps were fatigue-tested. The influence of fretting fatigue loading on the residual mechanical properties of the straps was also assessed, and although fretting fatigue represented an important limitation for laminated CFRP straps, it could be shown that the investigated CFRP tension members can compete with the well-established steel suspenders. Full article

(This article belongs to the Special Issue Selected Papers from "SMAR 2017")

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12 pages, 4678 KiB

Open AccessArticle

Fretting Fatigue Behaviour of Pin-Loaded Thermoset Carbon-Fibre-Reinforced Polymer (CFRP) Straps

by Fabio Baschnagel, Vanessa Rohr and Giovanni Pietro Terrasi

Polymers 2016, 8(4), 124; https://doi.org/10.3390/polym8040124 - 7 Apr 2016

Cited by 15 | Viewed by 7711

Abstract

This paper focuses on the fretting fatigue behaviour of pin-loaded carbon-fibre-reinforced polymer (CFRP) straps studied as models for rigging systems in sailing yachts, for suspenders of arch bridges and for pendent cables in cranes. Eight straps were subjected to an ultimate tensile strength test. In total, 26 straps were subjected to a fretting fatigue test, of which ten did not fail. An S–N curve was generated for a load ratio R of 0.1 and a frequency f of 10 Hz, showing a fatigue limit stress of the straps around the matrix fatigue limit, corresponding to 46% of the straps’ ultimate tensile strength (σ_UTS). The fatigue limit was defined as 3 million load cycles (N = 3 × 10⁶), but tests were even conducted up to N = 11.09 × 10⁶. Catastrophic failure of the straps was initiated in their vertex areas. Investigations on the residual strength and stiffness properties of straps tested around the fatigue limit stress (for N ≥ 1 × 10⁶) showed little influence of the fatigue loading on these properties. Quasi-static finite element analyses (FEA) were conducted. The results obtained from the FEA are in good agreement with the experiments and demonstrate a fibre parallel stress concentration in the vertex area of factor 1.3, under the realistic assumption of a coefficient of friction (cof) between pin and strap of 0.5. Full article

(This article belongs to the Collection Fiber-Reinforced Polymer Composites in Structural Engineering)

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17 pages, 4434 KiB

Open AccessArticle

Epoxy Enhanced by Recycled Milled Carbon Fibres in Adhesively-Bonded CFRP for Structural Strengthening

by Chao Wu, Peng Feng, Yu Bai and Ye Lu

Polymers 2014, 6(1), 76-92; https://doi.org/10.3390/polym6010076 - 31 Dec 2013

Cited by 13 | Viewed by 11973

Abstract

This paper investigates the mechanical performance and electrical resistivity of a structural adhesive epoxy enhanced using milled carbon fibre (MCF) as well as the bond performance of carbon fibre reinforced polymers (CFRP) and steel adhesively bonded joints using the enhanced epoxy. The epoxy was enhanced using such MCFs with different weight ratios of 1.5%, 3% and 5%. Tensile experiments were performed on the original and enhanced epoxy specimens according to ASTM D638. More ductile process failure was found for the epoxy after modification and significant improvements of E-modulus and tensile strength were evidenced when the MCF weight ratio was larger than 1.5%. Scanning electron microscopy (SEM) revealed that the failure mechanism of short MCFs pulled out from the epoxy matrix contributed to the enhancement of the mechanical performance of the epoxy. The electrical resistivity of the epoxy with MCF weight ratio of 5% was reduced by at least four orders of magnitude compared to the original epoxy, due to the conductive network formed by MCFs. Steel/CFRP double strap joints (with either CFRP sheets or CFRP laminates) were prepared using the enhanced epoxy and then tested in tension, however no obvious increase in joint stiffness or strength was observed. Full article

(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

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