Effect of in-plane fiber waviness defects on the compressive properties of quasi-isotropic thermoplastic composites

In this paper, a combination of experimentation and analysis is used to study the effect of micro in-plane fiber waviness on the compressive properties of unidirectional fabric composites. The experimental part includes a measurement of the micro in-plane fiber waviness in two types of unidirectional fabrics, manufacturing composites with each unidirectional fabric via VaRTM process and tests for establishing the compressive modulus and strengths of the composites. The compressive strengths were confirmed to be affected by the micro in-plane fiber waviness, but the compressive modulus was not. Furthermore, a two-dimensional numerical model is proposed to explain our experimental results. The numerical results indicate that the tensile stress (owing to the micro in-plane fiber waviness) and compressive stress along the weft and warp directions, respectively, of the composite lead to reductions in the compressive strength.

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Z-pin insertion process for through-thickness reinforced thermoplastic composites

Journal of Composite Materials ◽

10.1177/0021998318781233 ◽

2018 ◽

Vol 53 (2) ◽

pp. 173-181 ◽

Cited By ~ 3

Author(s):

Julian Hoffmann ◽

Alexander Brast ◽

Gerhard Scharr

Keyword(s):

Thermoplastic Composites ◽

Fiber Reinforced ◽

Fiber Waviness ◽

Reinforced Plastics ◽

Pullout Tests ◽

Glass Fiber Reinforced ◽

Reinforced Plastic ◽

Novel Method ◽

Fiber Reinforced Plastics ◽

Insertion Process

This paper presents a novel method for the ultrasonically assisted insertion of metallic z-pins into thermoplastic composites. Mechanical and microstructural investigations were carried out on glass fiber-reinforced polyamide and polypropylene specimens. The insertion of steel pins into thermoplastic composites led to microstructural changes that differ significantly from the known microstructure of z-pinned thermoset fiber-reinforced plastics. Optical microscopy showed an absence of notable fiber waviness and resin-rich zones around each pin. Instead, the fibers were predominantly deflected in the through-thickness direction by the high insertion forces arising during pin penetration. To gain an initial insight on the resulting properties of the z-pin/thermoplastic interface, the mechanical properties of z-pinned thermoplastic composites under mode I loading were investigated using pullout tests. For reference, the pullout behavior of thermoset carbon fiber-reinforced plastic specimens, reinforced with steel pins was determined too. Due to the poor bonding and lack of friction between the pin and laminate, the determined traction loads of the thermoplastic specimens are well below typical values achieved from pin pullout in thermoset laminates.

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Compressive properties of reversibly assembled lattice structures

Journal of Reinforced Plastics and Composites ◽

10.1177/0731684420970644 ◽

2020 ◽

pp. 073168442097064

Author(s):

Yueqing Zhao ◽

Mingyang Liu ◽

Tao Zhang ◽

Bo Xu ◽

Boming Zhang

Keyword(s):

Unit Cell ◽

Thermoplastic Composites ◽

Internal Space ◽

Lattice Structures ◽

Assembly Sequence ◽

Compressive Properties ◽

Cell Structures ◽

Glass Fiber Reinforced ◽

Shaped Part ◽

Space Volume

Lattice structures are competitive to fabricate sandwich structures for their excellent mechanical properties and large internal space volume. A non-planar cross-shaped part as a regular building block has been designed and manufactured using glass fiber-reinforced thermoplastic composites. Identical cross-shaped parts can be assembled into 120-unit cell lattice structures by a mechanical interlocking method. The compressive properties of unit cell lattice structures assembled with different connections pins and sequences were investigated. Lattices with steel pins possess higher compressive modulus and strength than those with composites pins. The compressive moduli of unit cell structures are more sensitive to assembly sequence than that of multi-cell structures. When the structures change to multi-cell from unit-cell with the same assembly sequence, the compressive moduli significantly decrease. The connection between face sheets and core by the ultrasonic welding improves the compressive properties of the structures. The reversible disassembly and strong designability of lattice structures are helpful to satisfy multifunctional requirements, meanwhile realizing energy saving and emission reduction.

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Environmental Effects on the Compressive Properties: Thermosetting vs. Thermoplastic Composites

Journal of Reinforced Plastics and Composites ◽

10.1177/073168449201100203 ◽

1992 ◽

Vol 11 (2) ◽

pp. 146-157 ◽

Cited By ~ 16

Author(s):

A. Haque ◽

S. Jeelani

Keyword(s):

Environmental Effects ◽

Thermoplastic Composites ◽

Compressive Properties

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An experimental approach to reproduce in-plane fiber waviness in thermoplastic composites test coupons using a reverse forming method

Journal of Composite Materials ◽

10.1177/00219983211026734 ◽

2021 ◽

pp. 002199832110267

Author(s):

RDR Sitohang ◽

WJB Grouve ◽

LL Warnet ◽

S Koussios ◽

R Akkerman

Keyword(s):

Experimental Approach ◽

Mechanical Performance ◽

Thermoplastic Composite ◽

Thermoplastic Composites ◽

Forming Process ◽

Fiber Waviness ◽

Manufacturing Method ◽

Main Challenge ◽

Defective Region ◽

Bend Angles

In-plane fiber waviness is one of the defects that can occur from the stamp-forming process of thermoplastic composite (TPC) parts. The influence of this defect on the mechanical performance of multidirectional composites is not yet fully understood. The main challenge in determining the influence on mechanical properties lies in reproducing the waviness in test coupons that can subsequently be subjected to testing. This paper describes an experimental approach to reproduce representative in-plane waviness defects, specific for TPC, by reverse-forming of V-shape parts of various bend angles and inner radii. Characterization results show that this method enables the manufacturing of localized in-plane waviness in flat 24-ply quasi-isotropic C/PEEK composites with no voids. Furthermore, laminates having varying levels of maximum waviness angle ([Formula: see text]), between 14° to 64°, were successfully produced in this work. By comparing the [Formula: see text] value with the examples of industrial stamp-formed parts, it can be concluded that the developed coupon manufacturing method can reproduce waviness from TPC part production reasonably well. Finally, all of the produced laminates have defective region lengths smaller than 20 mm, localized within a predefined location which makes them well suited for standard compression test coupons.

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Adding an expansive agent to increase the toughness of steel fibre reinforced concrete

HKIE Transactions ◽

10.33430/v26n4thie-2019-0001 ◽

2019 ◽

Vol 26 (4) ◽

pp. 197-208

Author(s):

Leo Gu Li ◽

Albert Kwok Hung Kwan

Keyword(s):

Reinforced Concrete ◽

Steel Fibre ◽

The Other ◽

Fibre Reinforced Concrete ◽

Test Results ◽

Compressive Properties ◽

Shrinkage Cracking ◽

Steel Fibre Reinforced Concrete ◽

Expansive Agent ◽

Concrete Matrix

Previous research studies have indicated that using fibres to improve crack resistance and applying expansive agent (EA) to compensate shrinkage are both effective methods to mitigate shrinkage cracking of concrete, and the additions of both fibres and EA can enhance the other performance attributes of concrete. In this study, an EA was added to fibre reinforced concrete (FRC) to produce concrete mixes with various water/binder (W/B) ratios, steel fibre (SF) contents and EA contents for testing of their workability and compressive properties. The test results showed that adding EA would slightly increase the superplasticiser (SP) demand and decrease the compressive strength, Young’s modulus and Poisson’s ratio, but significantly improve the toughness and specific toughness of the steel FRC produced. Such improvement in toughness may be attributed to the pre-stress of the concrete matrix and the confinement effect of the SFs due to the expansion of the concrete and the restraint of the SFs against such expansion.

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