Comparative study of metal and composite z-pins for delamination fracture and fatigue strengthening of composites

Published on Mar 1, 2016in Engineering Fracture Mechanics4.406
· DOI :10.1016/J.ENGFRACMECH.2016.01.003
K. Pingkarawat18
Estimated H-index: 18
(RMIT: RMIT University),
Adrian P. Mouritz71
Estimated H-index: 71
(RMIT: RMIT University)
Sources
Abstract
Abstract The influence of the material properties of z-pins on the mode I delamination properties of carbon–epoxy laminates is investigated. Improvements to the delamination fracture toughness and fatigue resistance of laminates reinforced in the through-thickness direction with z-pins made of metal (copper, titanium or stainless steel) or unidirectional carbon fibre composite is determined. Irrespective of the material, the z-pins are highly effective at increasing the fracture toughness and fatigue resistance by forming a large-scale bridging zone along delamination cracks. However, the fracture toughening and fatigue strengthening capacity of the z-pins is strongly dependent on their material properties, and increased in the order: copper (least effective), titanium, stainless steel and carbon fibre (most effective). The fracture and fatigue failure modes of the z-pins are also dependent on their material properties. The study reveals that improvements to the mode I fracture toughness and fatigue resistance can be optimized via a judicious choice of the z-pin material. Z-pins with high stiffness, strength and fatigue resistance (such as carbon fibre) provide the greatest improvement to the delamination toughness and fatigue strength.
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References21
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#1F. Pegorin (RMIT: RMIT University)H-Index: 5
#2K. Pingkarawat (RMIT: RMIT University)H-Index: 18
Last. Adrian P. Mouritz (RMIT: RMIT University)H-Index: 71
view all 4 authors...
The effect of z-pin length on the mode I and mode II delamination toughness and fatigue resistance of z-pinned carbon-epoxy composites is investigated. Experimental testing and mechanical modelling reveals that both the mode I fracture toughness and fatigue resistance increase with the z-pin length due to increased bridging traction loads generated by elastic stretching and pull-out of the pins. The opposite trend occurs for mode II toughness, which decreases with increasing z-pin length due to ...
Source
#1F. Pegorin (RMIT: RMIT University)H-Index: 5
#2K. Pingkarawat (RMIT: RMIT University)H-Index: 18
Last. Adrian P. Mouritz (RMIT: RMIT University)H-Index: 71
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This paper compares improvements to the mode I and mode II delamination fatigue resistance of an aerospace composite material achieved by z-pin reinforcement. Mode I (cyclic crack opening) and mode II (cyclic crack sliding) interlaminar fatigue tests were performed on a carbon fibre reinforced epoxy composite reinforced in the through-thickness direction with different volume contents and diameters of z-pins. Paris curves obtained from displacement-controlled fatigue tests reveal that z-pins are...
Source
#1F. Pegorin (RMIT: RMIT University)H-Index: 5
#2K. Pingkarawat (RMIT: RMIT University)H-Index: 18
Last. Adrian P. Mouritz (RMIT: RMIT University)H-Index: 71
view all 4 authors...
Improvements to the mode II delamination fatigue resistance of carbon fibre–epoxy composite by through-the-thickness reinforcement with z-pins are experimentally investigated. The effects of the volume content and diameter of z-pins on the mode II delamination crack growth rate and fatigue strengthening mechanisms of composites under interlaminar cyclic shear loading are investigated. Paris-like curves show the threshold cyclic stress intensity value to initiate mode II fatigue-induced growth of...
Source
#1K. Pingkarawat (RMIT: RMIT University)H-Index: 18
#2Adrian P. Mouritz (RMIT: RMIT University)H-Index: 71
Abstract This paper presents an experimental investigation into the mode I interlaminar fracture toughness and fatigue resistance of carbon fibre–epoxy laminate reinforced in the through-thickness direction with z-pins. The effects of the volume content, diameter and length of z-pins on the interlaminar toughness, fatigue resistance, and crack bridging toughening mechanisms are determined. The delamination crack growth rate under cyclic interlaminar loading slowed rapidly with increasing z-pin c...
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#1Han-Gi Son (Gyeongsang National University)H-Index: 1
#2Yong-Bin Park (Gyeongsang National University)H-Index: 8
Last. Jinho Choi (Gyeongsang National University)H-Index: 52
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Abstract In this study, the fatigue behaviour of stainless steel pin-reinforced cocured composite single-lap joints in a hygrothermal environment was experimentally investigated. Specimens were exposed to a temperature of 71 °C and a relative humidity of 85% until moisture saturation was achieved. Fatigue tests were conducted on the specimens in three different environmental conditions (RTD, room temperature and dry, ETD, elevated temperature and dry; and ETW, elevated temperature and wet). Tens...
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#1Adrian P. Mouritz (RMIT: RMIT University)H-Index: 71
#2T.M. Koh (RMIT: RMIT University)H-Index: 4
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Abstract The effect of hot–wet environment (75 °C and 85% relative humidity) on the delamination fracture properties and interlaminar toughening mechanisms of z-pinned carbon fibre–epoxy composite is investigated. The absorption rate of water from the hot–wet environment into the composite is accelerated slightly by z-pins, although the pins did not change the saturation limit of the material. Absorbed water weakens the pin/composite interface and this lowers the ultimate elastic traction load g...
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#1K. A. Mohammad (UPM: Universiti Putra Malaysia)H-Index: 1
#2A. Ali (UPM: Universiti Putra Malaysia)H-Index: 20
Last. Shahrum Abdullah (UKM: National University of Malaysia)H-Index: 17
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The aim of this work is to determine the fatigue life of 316L stainless steel. The mechanisms of fatigue of 316L stainless steels were investigated and discussed. The fatigue tests were carried out at constant-amplitude cyclic loading with load ratio R=0.1. Scanning Electron Microscope (SEM) is then used to examine the fracture surface. The results show that the fatigue limit of 316L stainless steel was 146.45 MPa.
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Z-pins are increasingly used to enhance the delamination toughness and impact damage tolerance of composite aircraft structures. An important consideration in the design of z-pinned structures is the deterioration of the in-plane mechanical properties of the composite material because of the pins. Experimental property data presented in this paper reveal that large improvements to the delamination toughness of carbon-epoxy composite gained with z-pins also result in an unavoidable reduction to t...
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Abstract Z-Pin reinforced carbon-fibre epoxy laminates were tested under Mode I and Mode II conditions, both quasi-statically and in fatigue. Test procedures were adapted from existing standard or pre-standard tests. Samples containing 2% and 4% areal densities of carbon-fibre Z-pins (0.28 mm diameter) were compared with unpinned laminates. Quasi-static tests under displacement control yielded a dramatic increase of the apparent delamination resistance. Specimens with 2% pin density failed in Mo...
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Abstract Z-pinned laminates and sandwich materials are an important class of composites with current applications in aircraft and emerging uses in other light-weight engineered products. This paper reviews research advances in the manufacture, microstructural chacterisation, mechanical properties, environmental durability and other functional properties (e.g. electrical, thermal, damage sensing) of z-pinned composite materials and structures. The review reveals that z-pins can be used in create ...
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