Automated fiber placement (AFP) is a composite manufacturing technique used to fabricate complex advanced air vehicle structures that are lightweight with superior qualities. The AFP process is ...intricate and complex with various phases of design, process planning, manufacturing, and inspection. An understanding of each of these phases is necessary to achieve the highest possible manufacturing quality. This literature review aims to summarize the entire AFP process from the design of the structure through inspection of the manufactured part to generate an overall understanding of the lifecycle of AFP manufacturing. The review culminates with highlighting the challenges and future directions for AFP with the goal of achieving a closed loop AFP process.
As part of an effort to predict wrinkling of carbon-fiber tows during automated fiber placement, the cohesive zone traction–separation relations for two carbon fiber epoxy prepreg tows are quantified ...for Mode I and Mode II loading using a rigid double cantilever beam (RDCB) specimen. An explicit expression for normal traction versus normal separation (
σ
vs
δ
n
) and tangential traction versus tangential separation
(
τ
vs
δ
t
)
are derived using static equilibrium equations for an RDCB considering a compressive zone ahead of the process zone. The traction–separation relationships are in term of quantities that can be measured using a full field measurement technique (StereoDIC). The baseline traction–separation relationships in this work are obtained using conditions representative of those experienced by an uncured tow undergoing automated fiber placement (AFP) onto a substrate of a similar material with layup temperature
T
=
40
∘
C
, pressure p = 1 MPa and contact time t = 1 s. The RDCB specimen is loaded in displacement control at a constant load line displacement rate of 0.3 mm/min. Speckle images for StereoDIC are captured using stereo vision systems equipped for capturing images of the RDCB specimen with a field of view of
100
mm
×
75
mm
. Analysis of the data obtained for Mode I and Mode II loading shows that the Mode I energy release rate
G
I
=
120
J
/
m
2
and Mode II energy release rate
G
II
=
255
J
/
m
2
, with the maximum normal traction
σ
max
=
0.50
MPa
and the maximum shear traction
τ
max
=
0.35
MPa
.
Automated Fiber Placement (AFP) is a flexible manufacturing technique which allows the manufacturing of complex layups where steered paths are necessary to achieve the surface coverage. However, ...steering tows using the AFP process introduces challenges in terms of quality and productivity due to steering induced defects. The quality of AFP layup is highly dependent on the geometry and the curvature of the path as well as the manufacturing process parameters such as layup temperature, head speed and compaction force. Understanding how these parameters affect the process is important to achieve the desirable quality of the final part. In this paper, several paths are steered at different radii of curvature (1270, 635 and 318 mm) on a cylindrical tool using different combinations of process parameters. The quality of the obtained layup is assessed through image processing of acquired profilometry scans. In-plane tow displacement and out-of-plane tow deformations are captured over the length of each placed course. Using numerical techniques, the defect occurrence is correlated to the input process parameters. Results show that the path curvature is the main feature driving defect formation. The remaining process parameters are ranked according to their influence.
As a contribution towards developing a platform for the mechanical characterization and eventual certification of steered fiber laminates, this paper presents a methodical breakdown of principal ...considerations. It is acknowledged that the synthesis of such a laminate will introduce curvilinear fibers that would result in a spatial variation in fiber orientation, which is one of the main characteristics that define the response of steered fiber laminates. The other important factors are identified as the presence of gaps and overlaps. Subsequently, the current publication proposes that these main characteristics interact to produce significantly complex stress-states in steered fiber laminates. By comparing the characteristics of steered fiber laminates with those of conventional laminates and laminates with ply drops, it is deduced that significant interlaminar stresses would develop especially at high stress gradient regions such as gaps and overlaps. Research on the examination of the effect of the principal factors – fiber orientation, interlaminar stresses, gaps and overlaps, are discussed in the context of the characterization and certification. For every principal factor, corresponding discussions are constructed by a review of literature firstly regarding their nature and existing methods for quantifying them, and secondly related to their implementation in characterization frameworks.
This paper presents a thorough investigation of wrinkling within a path on a general surface for a composite tow constructed using the AFP process. Governing equations and assumptions for the ...presented model are derived based on geometrical considerations. A simple form of the wrinkled shape is assumed and applied to the inner edge of the tow path. For a given wavelength, the amplitude of the wrinkles can be approximated based on a worst-case scenario where all the difference in length between the edges of the path is absorbed through an out-of-plane wrinkle. The wrinkle wavelength can be obtained either from existing mechanics models in the literature or experimental measurements, otherwise an adequate wavelength can be assumed. A numerical solution is implemented to visualize wrinkles on the curved paths and to indicate potential regions for wrinkling on the surface. Several examples are presented to demonstrate the model, including constant angle paths on a double-curved surface and curved paths on a flat surface. From a geometrical standpoint, increasing the tow width or the path curvature results in an increase in the wrinkles’ amplitude. Calculation of the wrinkles’ amplitude for a steered path on flat surface shows good agreement with experimental measurements.
Since the arrival of Automated Fiber Placement (AFP) in the 1980s and 1990s, the manufacturing technique has been progressively improving in quality and reliability of the process and resulting ...structures. The state-of-the-art of AFP is allowing for the manufacture of structures with increasing geometrical complexity. To adequately manufacture such structures, a large effort in process planning is required to reduce defect occurrence to the best extent possible. Many optimization methodologies have been established for AFP in terms of the design and process parameters. However, limited work has been accomplished in terms of process planning optimization. The work presented in the latter will develop a Bayesian Optimization (BO) technique for the optimization of process planning with the use of the Computer Aided Process Planning (CAPP) software and its connection with Vericut Composite Programming (VCP). A case study is performed on a doubly curved tool surface and the optimal solution is compared with as-manufactured results for validation. A predictive tool is also developed to rank layup strategies based on defect importance. Results show a substantial improvement in defect occurrence and allow a process planner to immediately see the performance of various layup strategies and starting point combinations.
For the first time, an experimental investigation is presented quantifying out-of-plane wrinkle formation and in-plane deformations occurring in prepreg slit tape specimens during automated fiber ...placement (AFP). The AFP process is conducted on 6.35 mm wide individual prepreg tows that are placed along a straight path and steered along circular paths with radii of curvature, ρ = 2540 mm, 1270 mm and 305 mm. Full-field shape, displacement and strain measurements are obtained using StereoDIC in three successive stages; (i) immediately after lay-up of the tow, (ii) one hour after lay-up and (iii) after reheating of the as-placed tow by traversing the AFP head close to the tow path and exposing the specimen to the same levels of heating as employed during the initial lay-up (without compaction pressure). Measurements obtained in stage (i) showed that (a) all tows exhibited local wrinkling at locations where the underlying substrate had defects (e.g., gaps, overlaps), (b) excluding the substrate defect locations, tows steered with ρ = 2540 mm showed no evidence of additional out-of-plane wrinkling after placement, (c) tows steered with ρ = 1270 mm exhibited several small amplitude wrinkles initiated at locations outside the substrate overlap regions and (d) tows steered with ρ = 305 mm incurred significant additional localized wrinkling along the inner radius of the tow with an increase in both the amplitude and frequency of the wrinkles. In addition, higher variability in the wrinkle wavelength is observed for ρ = 305 mm. Measurements obtained in stages (ii) and (iii) showed an increase in wrinkle amplitude, indicating that wrinkle amplitude is a function of both time and temperature for an as-placed tow.
•Viscoelastic behavior of uncured tows determined experimentally in relevant temperature range.•Measurements show tow obeys time temperature superposition principle (TTSP)•WLF and Arrhenius models ...are excellent fits to data.•TTSP for WLF model provide results over 9 decades of time.•Data shows tow is elastic during wrinkle formation in AFP manufacturing of thermoset composite components.
In support of computational modeling of tow placement at elevated temperature, the creep response of IM7/8552 uncured prepreg slit tape material during 3-point bend loading at different temperatures is measured using an RSA III dynamic mechanical analyzer. Short term creep experiments were conducted for a duration of 1000 s at ten different temperatures ranging from −5°C (below Tg of 0 °C) to 40 °C, with the latter being the nominal processing temperature for the tow. Results show that the tow material obeys the time-temperature superposition principle (TTSP) in the temperature range selected for the creep experiments. Using the TTSP, creep compliance master curve spanning more than eight logarithmic decades is obtained for the nominal processing temperature of 40 °C. The time–temperature shift factor is observed to follow closely the William-Landel-Ferry (WLF) model, with the WLF parameters obtained by least square fitting of the experimentally determined shift factors utilizing closed form shifting algorithm (CFS). The WLF model for the material is used to extend the master curve to a range of temperatures above glass transition temperature (Tg) of the material. The creep compliance data is further employed to obtain the retardation spectra of the material using an algorithm based on the work of a co-author and applied recently to a different material system by the authors. Details for extraction of the retardation spectra from the creep compliance results are provided. Results from these studies demonstrate that the creep compliance reconstructed from the retardation spectra accurately represent the experimental results while providing baseline data to quantify the importance of viscoelastic behavior in wrinkle formation during advanced manufacturing of aerospace components.
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