The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

Self-healing polymeric materials: A review of recent developments

Highly consistent quality and cost-effective manufacture of advanced composites can be achieved through automation. It may therefore open up new markets and applications for composite products in aerospace, automotive, renewable energy, and consumer goods. Automated Tape Laying (ATL) and Automated Fibre Placement (AFP) are the two main technologies used to automate the layup of prepreg. The historical development and past research of both technologies is reviewed; with an emphasis on past issues in application and capability as well as their solution, including both thermoset and thermoplastic material layup. It is shown that past developments have moved away from simply emulating manual layup into the now unique layup procedures for ATL, and into the current AFP technology base. The state of the art for both technologies is discussed and current gaps in the understanding of both processes highlighted. From this, future research needs and developments are derived and discussed.

The engineering aspects of automated prepreg layup: History, present and future

Thermal therapy is one of the most popular physiotherapies and it is particularly useful for treating joint injuries. Conventional devices adapted for thermal therapy including heat packs and wraps have often caused discomfort to their wearers because of their rigidity and heavy weight. In our study, we developed a soft, thin, and stretchable heater by using a nanocomposite of silver nanowires and a thermoplastic elastomer. A ligand exchange reaction enabled the formation of a highly conductive and homogeneous nanocomposite. By patterning the nanocomposite with serpentine-mesh structures, conformal lamination of devices on curvilinear joints and effective heat transfer even during motion were achieved. The combination of homogeneous conductive elastomer, stretchable design, and a custom-designed electronic band created a novel wearable system for long-term, continuous articular thermotherapy.

Stretchable Heater Using Ligand-Exchanged Silver Nanowire Nanocomposite for Wearable Articular Thermotherapy

Artificial muscles hold promise for safe and powerful actuation for myriad common machines and robots. However, the design, fabrication, and implementation of artificial muscles are often limited by their material costs, operating principle, scalability, and single-degree-of-freedom contractile actuation motions. Here we propose an architecture for fluid-driven origami-inspired artificial muscles. This concept requires only a compressible skeleton, a flexible skin, and a fluid medium. A mechanical model is developed to explain the interaction of the three components. A fabrication method is introduced to rapidly manufacture low-cost artificial muscles using various materials and at multiple scales. The artificial muscles can be programed to achieve multiaxial motions including contraction, bending, and torsion. These motions can be aggregated into systems with multiple degrees of freedom, which are able to produce controllable motions at different rates. Our artificial muscles can be driven by fluids at negative pressures (relative to ambient). This feature makes actuation safer than most other fluidic artificial muscles that operate with positive pressures. Experiments reveal that these muscles can contract over 90% of their initial lengths, generate stresses of ∼600 kPa, and produce peak power densities over 2 kW/kg-all equal to, or in excess of, natural muscle. This architecture for artificial muscles opens the door to rapid design and low-cost fabrication of actuation systems for numerous applications at multiple scales, ranging from miniature medical devices to wearable robotic exoskeletons to large deployable structures for space exploration.

https://www.pnas.org/content/pnas/114/50/13132.full.pdf

Fluid-driven origami-inspired artificial muscles

Joining of thermoplastic composites is an important step in the manufacturing of aerospace thermoplastic composite structures. Therefore, several joining methods for thermoplastic composite components have been under investigation and development. In general, joining of thermoplastic composites can be categorized into mechanical fastening, adhesive bonding, solvent bonding, co-consolidation, and fusion bonding or welding. Fusion bonding or welding has great potential for the joining, assembly, and repair of thermoplastic composite components and also offers many advantages over other joining techniques. The process of fusion-bonding involves heating and melting the polymer on the bond surfaces of the components and then pressing these surfaces together for polymer solidification and consolidation. The focus of this paper is to review the different fusion-bonding methods for thermoplastic composite components and present recent developments in this area. The various welding techniques and the corresponding manufacturing methodologies, the required equipment, the effects of processing parameters on weld performance and quality, the advantages/disadvantages of each technique, and the applications are described.

https://journals.sagepub.com/doi/pdf/10.1177/0892705704045187

Fusion Bonding/Welding of Thermoplastic Composites

The Automated Fiber placement (AFP) process shows great potential for efficient manufacturing of large composite structures. However, uncertainties exist on mechanical performance of final product that are associated with the process induced defects. This experimental work investigates the effect of four principal defect types, namely gap, overlap, half gap/overlap and twisted tow on the ultimate strengths. Tests are executed at the lamina level (fiber tension, fiber compression and in-plane shear), as well as at the laminate level (open hole tension and open hole compression). Then each test is compared with a baseline configuration exempt from defects. Tests have revealed the minimal effects of a single and isolated defects on mechanical performance especially at the lamina level (around 5%) compared to the laminate level (up to 13%).

/pdf/experimental-study-of-the-effect-of-automated-fiber-1w36x6r0f9.pdf

Experimental study of the effect of automated fiber placement induced defects on performance of composite laminates

Fiber-reinforced composite materials are replacing metallic components due to their higher specific strength and stiffness. Automation and thermoplastics emerged to overcome the time and labor inte...

Processing of thermoplastic matrix composites through automated fiber placement and tape laying methods: A review

The bending-induced buckling improvement in a variable stiffness (VS) composite cylinder (made by fiber steering) is studied. For such a cylinder, the effect of the variation of the direction of the load on its buckling performance of the cylinder is also examined. Compromise programming, as a multi-objective optimization method, is used to design for buckling of the VS cylinder subjected to bending load in either of the two opposite directions. Different combinations of weight factors for the structural performance in the two opposite directions were also applied to obtain the Pareto frontier as the main decision making tool for the designers in a multi-objective design problem.

Multi-objective design optimization of variable stiffness composite cylinders

https://paginas.fe.up.pt/~iccs16/CD/121-160/158ShadmehriHoaHojjati.pdf

Mehdi Hojjati

Papers

Fusion Bonding/Welding of Thermoplastic Composites

Experimental study of the effect of automated fiber placement induced defects on performance of composite laminates

Processing of thermoplastic matrix composites through automated fiber placement and tape laying methods: A review

Multi-objective design optimization of variable stiffness composite cylinders

Buckling of conical composite shells