New double indentation technique for measurement of the elasticity modulus of thin objects

In this paper we introduce a new method to determine the Young's modulus of thin (biological) samples. The method is especially suitable for small objects with a thickness of a few hundred micrometers. Such specimens cannot be examined with existing tests: compression and tensile tests need well-known geometry and boundary conditions while classic indentation tests need relatively thick pieces of material. In order to determine the elastic modulus we use the indentation theory as proposed by Sneddon and correct it with a finite element calculated kappa factor to compensate for the small thickness. In order to avoid material deformations at the contact zone between the sample bottom and the sample stage, we replace the sample stage by a second indentation needle. In this way the sample can be clamped between two identical needles and a virtual mirror plane is introduced. The new method was used on four test-materials and results agreed well with the outcome of a standard compression method applied on large samples of the same materials. As an application example the technique was applied on thin biological samples, namely middle ear ossicles of rabbits

Fusion bonding of carbon fabric reinforced polyphenylene sulphide

In recent years, there is a growing interest in joining techniques for thermoplastic composites as an alternative to adhesive bonding. In this manuscript, a fusion bonding process called hot-tool welding is investigated for this purpose and the used material is a carbon fabric reinforced polyphenylene sulphide. The quality of the welds is experimentally assessed using a short three-point bending setup, which has an interesting distribution of interlaminar shear stresses. It can be concluded that although the hot-tool welding process shows high short-beam strengths, it has some drawbacks. Therefore, a design of an infrared welding setup is presented

Feasibility study of fusion bonding for carbon fabric reinforced Polyphenylene Sulphide by hot-tool welding

In recent years, there is a growing interest in joining techniques for thermoplastic composites as an alternative to adhesive bonding. In this article, a fusion bonding process called hot-tool welding is investigated for this purpose and the used material is a carbon fabric reinforced polyphenylene sulphide. The welds are first observed through a microscope, after which the quality is experimentally assessed using a short three-point bending setup. A comparison is made between the welded specimens and the equivalent hot pressed specimens. It can be concluded that the hot-tool welding process is very promising for the welding of material under study and that the short three-point bending setup proves interesting for evaluating bonds between composite specimens

On the orthotropic elasto-plastic material response of additively manufactured polyamide 12

The mechanical response of polymers such as polyamide 12 (PA-12) manufactured through additive manufac-turing, is significantly affected by the layered manufacturing approach and the printer settings used during the creation of the parts. As a result, the mechanical performance can differ significantly from PA-12 parts creat-ed through conventional techniques such as injection molding, and a detailed study of the material mechanical behavior is necessary. This work presents an in-depth study of the response of PA-12 to tensile loading and the challenges involved in obtaining qualitative and repeatable results. The full elasto-plastic curves are meas-ured during tensile testing and the effect of printing direction is taken into account in order to investigate whether orthotropic material behavior can be observed. All parts were manufactured using commercially avail-able selective laser sintering (SLS) printers. Digital image correlation was used extensively to obtain high-accuracy strain measurement over the entire elasto-plastic range up to failure. The results show an isotropic elastic response of PA-12, with orthotropic failure properties and the presence of significant viscous contribu-tions in the material response

Influence of specimen geometry on the fatigue behavior of a carbon fabric reinforced pps

This manuscript studies the tension-tension fatigue behavior of a carbon fabric reinforced PPS and the influence of the specimen geometry on the obtained results. First, the fatigue experiments are preformed according to the ASTM D3479/D3479M standard using the rectangular shaped specimen, but virtually all specimens fail in the tabbed section. This, however, means that fatigue lifetime may be underestimated. Therefore, a new dumbbell-like shape was assessed. Based on the occurring stress concentrations in the tabbed section, the dog bone-like shape was first optimised numerically using FEM, and then, the optimised specimen was tested in tension-tension fatigue. It can be concluded that this dumbbell shape yields better results in terms of acceptable failure and that the used shape has a significant influence on the fatigue lifetime