Flat-Top Cylinder Indenter for Mechanical Characterization: A Report of Industrial Applications

FIMEC (flat-top cylinder indenter for mechanical characterisation) is an instrumented indentation test employing a cylindrical punch. It has been used to determine the mechanical properties of metallic materials in several applications of industrial interest. This work briefly describes the technique and the theory of indentation with a flat-ended punch. The flat indentation of metals has been investigated through experimental tests, and an equation has been derived to calculate the yield stress from the experimental data in deep indentation. The approach is supported by many data on various metals and alloys. Some selected case studies are presented in the paper: (i) crank manufacturing through pin squeeze casting; (ii) the evaluation of the local mechanical properties in a carter of complex geometry; (iii) the qualification of Al billets for extrusion; (iv) stress–relaxation tests on CuCrZr heat sinks; (v) the characterization of thick W coatings on CuCrZr alloy; (vi) the measure of the local mechanical properties of the molten-zone (MZ) and the heat-affected zone (HAZ) in welded joints. The case studies demonstrate the great versatility of the FIMEC test which provides information not available by employing conventional experimental techniques such as tensile, bending, and hardness tests. On the basis of theoretical knowledge and large amount of experimental data, FIMEC has become a mature technique for application on a large scale in industrial practice.

Deep Indentation and Puncture of a Rigid Cylinder Inserted into a Soft Solid

Deep indentation and puncture can be used to characterize the large strain elastic and fracture properties of soft solids and biological tissues. While this characterization method is growing in application...

Surgical Management of Intraocular Silicone Oil Microdroplet

Purpose Intraocular silicone oil microdroplets have been described after intravitreal injection of anti-VEGF agents packaged at a compound pharmacy. We present a case with the presence of an intraocular silicone oil microdroplet after a vitreoretinal operation using disposable instruments, and the surgical technique for its removal. Methods A 59-year-old patient who had been operated on for vitreous opacities using a disposable 27-g vitrectomy kit complained of a small round structure floating in the eye. It appeared a few days after surgery. The bubble was not present at all times and it disappeared for days on end. Clinical examination of the vitreous and retina during these uneventful periods was normal. The bubble reappeared intermittently without a link to any specific movement for some time but was again absent once the patient was examined. The physical properties of the mobile round lesion could be identified as lighter than aqueous humor, as it was described as being in the center of the visual field if the head was tilted forward. Results As the patient was very bothered by this bubble, a 23-g vitrectomy was performed. During deep indentation of the pars plana over 360 degrees, a tiny bubble of silicone oil could be found buried in the peripheral vitreous base, and controlled aspiration under deep indentation was performed. The patient has been without symptoms since the removal of the droplet and made an uneventful clinical recovery. Conclusion Microdroplets of silicone oil may be present in disposable vitreoretinal instruments and stay in the eye after surgery, causing a visual disturbance. The origin of these droplets may be linked to the plastic tubing of the instruments.

Inferring the ballistic resistance of thick targets from static deep indentation tests

The aim of this work is to demonstrate that one can derive the value of the dynamic resistive stress, which a given target exerts on a rigid projectile, by following the force needed to push a rigid indenter into the target in a static deep indentation test. In this study, we used a relatively soft target made of a lead-antimony alloy and a concrete target, representing ductile metals and brittle solids, respectively. For both targets, we followed the force–distance curves obtained by the deep indentations of hard punches, as they were slowly pushed in the targets by a loading frame. The effect of friction during these tests was taken into account in order to obtain the net axial resisting stresses, which were applied by the targets on these indenters. These static resisting stresses, at deep penetrations, were compared with the dynamic resisting stresses, which were inferred from the impacts of armor-piercing projectiles on these targets. The good agreement between the two sets of values strongly enhances the claim that one can use static indentation tests in order to estimate the ballistic resistance of various targets to rigid projectile penetration. The effect of strain rate sensitivity is highlighted by the test results for both the metallic and concrete targets. In addition, important insights concerning the cavitation phenomenon in the penetration of rigid projectiles are also highlighted in this work.

Prediction of Asymmetric Yield Strengths of Polymeric Materials at Tension and Compression Using Spherical Indentation

Engineering polymers generally exhibit asymmetric yield strength in tension and compression due to different arrangements of molecular structures in response to external loadings. For the polymeric materials whose plastic behavior follows the Drucker–Prager yield criterion, the present study proposes a new method to predict both tensile and compressive yield strength utilizing instrumented spherical indentation. Our method is decomposed into two parts based on the depth of indentation, shallow indentation, and deep indentation. The shallow indentation is targeted to study elastic deformation of materials, and is used to estimate Young's modulus and yield strength in compression; the deep indentation is used to achieve full plastic deformation of materials and extract the parameters in Drucker–Prager yield criterion associated with both tensile and compressive yield strength. Extensive numerical computations via finite element method (FEM) are performed to build a dimensionless function that can be employed to describe the quantitative relationship between indentation force-depth curves and material parameters of relevance to yield criterion. A reverse algorithm is developed to determine the material properties and its robustness is verified by performing both numerical and experimental analysis.

Pull-off characteristics of double-shanked compared to single-shanked ligation clips: an animal study

Background: The use of surgical ligation clips is considered as the gold standard for the closure of vessels, particularly in laparoscopic surgery. The safety of clips is mainly achieved by the deep indentation of the metal bar with a high retention force. A novel double-shanked (DS) titanium clip was compared to two single-shanked clips with respect to axial and radial pull-off forces.Methods: In a porcine model (8 animals, 51±1 kg), arteries were prepared immediately after euthanisation, assigned to either a medium (2–4 mm; n=120) or a medium-large (3.5–7 mm; n=120) clip size group, and clipped with the appropriate clip size. After dissection, axial and radial pull-off forces were measured.Results: The axial pull-off force of the DS-Clip was higher than one single-shanked clip and comparable to the other single-shanked clip, and overall was linearly correlated to the cross-sectional area of the clip. The radial pull-off force of the DS-Clip was significantly higher than both single-shanked clips and, for the single-shanked clips, was correlated to the total clip thickness. The variation of radial pull-off force was lower for the DS-Clip due to a defined catch in the clip applier.Conclusions: The radial pull-off force was lower than the axial pull-off force in total and therefore appears to be the critical point of dislocation. Due to the higher total holding mass, the DS-Clip provided a clear advantage in this regard and might therefore decrease the dislocation rate. The catch in the applier increases the reproducibility in clip placement.

Indentation Behavior of a Closed-Cell Aluminum Foam at Elevated Temperatures

A series of deep indentation and uniaxial compression tests of closed-cell aluminum foams at room temperature as well as elevated temperatures were conducted. A flat-ended punch (FEP) was used in the indentation tests. Cross-sectional views of the specimens after tests show that the deformation is roughly confined to the material directly underneath the indenter with slightly lateral spread. It is found that plastic collapse strength and energy absorption of the specimens are temperature dependent in both loading conditions. Tear energy of the foam in FEP indentation depends on the indentation depth and temperature.

Simulation of Deep Spherical Indentation Using Eulerian Finite Element Methods

Simulation of deep indentation, and the associated pile-up effects, requires a robust and accurate finite element model capable of naturally handling the large deformations present. This work successfully demonstrates that the Eulerian formulation is capable of accurately reproducing the forces and general material response of deep indentation. It was found that, in the absence of friction, sink-in dominates at indentation depths less than 1.1% of the indenter radius, there is a transition from sink-in to pile-up from 1.1% to 2.3% of the indenter radius, and pile-up is fully developed at indentation depths larger than 13.2% of the indenter radius for the 4340 steel workpiece and the 0.508 mm radius indenter presented in this work. Friction tended to marginally increase the sink-in and transition depths as well as reduce the material height at the onset of fully developed pile-up due to a reduction in the tensile radial strain directly under the indenter.