Development of composite springs using 4D printing method

Composite springs have been used in many engineering applications, particularly in the transportation industry. This is due to their light weight, good stiffness, good strength, good corrosion and fatigue resistances. Normally special molds need to be prepared in the manufacturing of these springs. The molds have curvatures which fit into the shape of the final product. Recently the concept of 4D printing of composites was introduced. This concept is a combination of 3D printing together with the reconfiguration of the part upon the activation of some mechanism such as heat, light, or the absorption of moisture. This concept allows the ability to make structures of complex shapes without the need to have complex molds. Layers of composites can be laid on a flat mold. Upon curing, the layers reconfigure into curved structures. As such, curved composite structures can be made using only flat molds. The mechanism for this reconfiguration depends on the anisotropic nature of layered composite materials. This paper presents the fundamental study, as part of a larger project intended to use the concept of 4D printing to develop complex composite structures without the need for complex curved molds. The fundamental study examines the mechanical characteristics of curved composite beams made by 4D printing

Design Of Hard Compaction Rollers For Automated Fiber Placement On Complex Mandrel Geometries

This paper presents a methodology for designing hard compaction rollers for an automated fiber placement (AFP) head with a hot gas torch heating system for laying thermoplastic carbon fiber reinforced plastic (CFRP) tapes. Some manufacturing defects and alternative designs are reviewed to highlight the importance of AFP compaction roller conformity and surface adhesion. The formulation of a general parametric description of the design challenge is derived and adequately addresses the problem on a tow-to-tow basis

Electrical resistance of CNT-PEEK composites under compression at different temperatures

Electrically conductive polymers reinforced with carbon nanotubes (CNTs) have generated a great deal of scientific and industrial interest in the last few years. Advanced thermoplastic composites made of three different weight percentages (8%, 9%, and 10%) of multiwalled CNTs and polyether ether ketone (PEEK) were prepared by shear mixing process. The temperature- and pressure-dependent electrical resistance of these CNT-PEEK composites have been studied and presented in this paper. It has been found that electrical resistance decreases significantly with the application of heat and pressure

Digital Image Correlation Applications in Composite Automated Manufacturing, Inspection, and Testing

Since its advent in the 1970s, digital image correlation (DIC) applications have been rapidly growing in different engineering fields including composite material testing and analysis. DIC combined with a stereo camera system offers full-field measurements of three-dimensional shapes, deformations (i.e., in-plane and out-of-plane deformations), and surface strains, which are of most interest in many structural testing applications. DIC systems have been used in many conventional structural testing applications in composite structures. However, DIC applications in automated composite manufacturing and inspection are scarce. There are challenges in inspection of a composite ply during automated manufacturing of composites and in measuring transient strain during in-situ manufacturing of thermoplastic composites. This article presents methodologies using DIC techniques to address these challenges. First, a few case studies where DIC was used in composite structural testing are presented, followed by development of new applications for DIC in composite manufacturing and inspection

Bifurcation points in unsymmetric laminates and their influence on lay-up design for 4D printing of composites

4D printing of composites (4DPC) is a technique that can make composite structures with curved geometry without the need to use a curved mold (only a flat mold is used). This technique has been used to make composite springs and cones, where not only the shape is obtained but the mechanical properties are equivalent to those made using conventional technique (where a curved mold is used). The principle of operation of 4DPC utilized anisotropy in unsymmetric laminates as the mechanism for the shape transformation. However it is not always straightforward that a certain unsymmetric lay-up of composite layers will provide a certain shape. Hyer [1,2] observed that laminate theory is accurate to predict the shape of the [0/90] laminate only in some cases, but not in all cases. He attributed this to the assumption of linear relation between the strains and displacements. He then used the non-linear relation between strains and displacements and assumed some functional forms for them. This approach was able to predict the shape of square thin laminates such as those made of [0/90] and [02/902] lay sequences, but not for rectangular laminates or laminates of other shapes. Finite element method was also used for this prediction. This method worked only with some twikking of the modeling procedure. As such work of previous researchers in the past more than 40 years only show success in ad-hoc situations. The reason for this is due to the lack of an explanation for why there are so many different shapes in different situations. The work in this paper provides an explanation as to why there are different shapes for different situations. This understanding provides a direction for the development of a new finite element procedure that can determine the shape of the laminates in different situations. The new understanding is used to explain the behavior of many cases. This new finite element procedure is then used to generate guidelines on the effect of different parameters such as the effect of geometric dimensions, and material properties on the final shape. These guidelines are useful for the selection of lay-up sequences to make structures in the technique of 4D printing of composites