Investigation of Quasi-Static Indentation Response of Inkjet Printed Sandwich Structures under Various Indenter Geometries

Damage Assessment of Glass-Fibre-Reinforced Plastic Structures under Quasi-Static Indentation with Acoustic Emission

The use of fibre-reinforced plastics (FRPs) in various industrial applications continues to increase thanks to their good strength-to-weight ratio and impact resistance, as well as the high strength that provides engineers with advanced options for the design of modern structures subjected to a variety of out-of-plane impacts. An assessment of the damage morphology under such conditions using non-destructive techniques could provide useful data for material design and optimisation. This study investigated the damage mechanism and energy-absorption characteristics of E-glass laminates and sandwich structures with GFRP face sheets with PVC cores under quasi-static indentation with conical, square, and hemispherical indenters. An acoustic emission (AE) technique, coupled with a k-means++ pattern-recognition algorithm, was employed to identify the dominant microscopic and macroscopic damage mechanisms. Additionally, a post-mortem damage assessment was performed with X-ray micro computed tomography and scanning electron microscopy to validate the identified clusters. It was found that the specific energy absorption after impact with the square and hemispherical indenters of the GFRP sandwich and the plain laminate differed significantly, by 19.29% and 43.33%, respectively, while a minimal difference of 3.5% was recorded for the conical indenter. Additionally, the results obtained with the clustering technique applied to the acoustic emission signals detected the main damaged modes, such as matrix cracking, fibre/matrix debonding, delamination, the debonding of face sheets/core, and core failure. The results therefore could provide a methodology for the optimisation and prediction of damage for the health monitoring of composites.

Influence of Post-Processing on the Properties of Multi-Material Parts Obtained by Material Projection AM

The great geometric complexity that additive manufacturing allows in parts, together with the possibility of combining several materials in the same part, establishes a new design and manufacturing paradigm. Despite the interest of many leading sectors, the lack of standardization still makes it necessary to carry out characterization work to enjoy these advantages in functional parts. In many of these techniques, the process does not end with the end of the machine cycle, but different post-processing must be carried out to consider the part finished. It has been found that the type of post process applied can have a similar effect on part quality as other further studied process parameters. In this work, the material projection technique was used to manufacture multi-material parts combining resins with different mechanical properties. The influence of different post-processing on the tensile behavior of these parts was analyzed. The results show the detrimental effect of ultrasonic treatment with isopropyl alcohol in the case of the more flexible resin mixtures, being advisable to use ultrasonic with mineral oil or furnace treatment. For more rigid mixtures, the furnace is the best option, although the other post-processing techniques do not significantly deteriorate their performance.

Urogynecological surgical mesh implants: New trends in materials, manufacturing and therapeutic approaches

Pelvic Organ Prolapse (POP) and Stress Urinary Incontinence (SUI) are two prevalent disorders affecting 30-40% of women worldwide. Current strategies to repair or improve these medical conditions are non-surgical options such as physiotherapy, or surgical options such as the use of vaginal meshes. The synthetic material polypropylene (PP), which has long been used for manufacturing these vaginal meshes, is associated with severe complications such as chronic pain, infection or mesh erosion. As a result of a widespread reporting and unacceptably high rates of complications, these issues have become a public health concern. Regulatory bodies have recently deemed the transvaginal placement of PP mesh in the pelvic floor (PF) no longer a suitable treatment method for PF repair, leading to the need for a novel approach to the manufacture and selection of materials for urogynecological meshes. Medical devices, such as vaginal meshes can be manufactured using a variety of techniques including injection moulding, electrospinning, hot-melt extrusion (HME) or more recently 3D printing. Over the past decade, the use of 3D printing within the medical device industry has expanded and offers a promising approach to manufacture patient-specific surgical mesh when combined with imaging tools. This review will summarise the current strategies to treat POP and SUI, the issues and use of current meshes for the treatment of these pelvic floor disorders (PFDs), and the future directions for the manufacture of more suitable urogynecological meshes, as well as their potential materials.

Recent Patents in Additive Manufacturing of Continuous Fiber Reinforced Composites

Background:

Additive Manufacturing (AM) enables the accurate fabrication of designed parts in a short time without the need for specific molds and tools. Although polymers are the most widely used raw materials for AM, the products printed by them are inherently weak, unable to sustain large tension or bending stresses. A need for the manufacturing of fiber reinforced composites, especially continuous fiber as reinforcement, has attracted great attention in recent years.

Objective:

Identifying the progress of the AM of continuous carbon fiber reinforced composites over time and therefore establishing a foundation on which current research can be based.

Methods:

Elaborating the most related patents regarding the AM techniques for fabricating continuous fiber reinforced composites in the top three institutions, including Markforged company, Xi’an Jiaotong University and President and Fellows of Harvard College.

Results:

The recent patents in AM of continuous fiber reinforced composites are classified into two aspects: patents related to novel technique methods and patents related to novel structures. The current issues and future development of AM-based composites are given.

Conclusion:

New structures and techniques have been introduced into conventional 3D printers to enable the printing of continuous fiber reinforced composites. However, until now, Markforged is the only company commercializing the fabrication of this kind of composites based on AM technique. Numerous challenges and issues need to be solved so that AM of continuous fiber reinforced composites can be a new manufacturing method.

3D Printing and Bioprinting in MEMS Technology

3D printing and bioprinting have advanced significantly in printing resolution in recent years, which presents a great potential for fabricating small and complex features suitable for microelectromechanical systems (MEMS) with new functionalities. This special issue aims to give a glimpse into the future of this research field.