Soft projectile impact forces measurement using Hopkinson bars: application to ice, artificial bird and rubber

This work presents an experimental campaign of impacts of soft projectiles to measure the induced force during the impact. Three different materials acting as soft impactors that could strike against a aeronautical structural component: ice, artificial bird and rubber have been impacted at several velocities against an aluminium Hopkinson bar. This device has been instrumented with semiconductor strain gauges that allow to obtain the induced compression strain. Additionally, all the impacts were recorded using high-speed video cameras, allowing the kinematic analysis of the projectile during the impact. After the results study, it has been concluded that there is a linear dependency between the kinetic energy and the peak force for all three materials. Added to that, it has been proved that the higher peak force corresponds to ice, despite the kinetic energy, followed by rubber and finally the artificial bird. In addition, while ice and artificial bird projectiles get radially dispersed after the impact, rubber spheres rebound due to its different behaviour. The obtained data is of great interest to design structures which could be subjected to impacts of soft materials such as aeronautic structures

Strain State Detection in Composite Structures: Review and New Challenges

Developing an advanced monitoring system for strain measurements on structural components represents a significant task, both in relation to testing of in-service parameters and early identification of structural problems. This paper aims to provide a state-of-the-art review on strain detection techniques in composite structures. The review represented a good opportunity for direct comparison of different novel strain measurement techniques. Fibers Bragg grating (FBG) was discussed as well as non-contact techniques together with semiconductor strain gauges (SGs), specifically infrared (IR) thermography and the digital image correlation (DIC) applied in order to detect strain and failure growth during the tests. The challenges of the research community are finally discussed by opening the current scenario to new objectives and industrial applications.

Measurement of Strain Using Strain Gauge and Piezoelectric Sensors

Today, measurement of strain plays a crucial role in different areas of research such as manufacturing, aerospace, automotive industry, agriculture, and medical. Many researchers have used different types of strain transducers to measure strain in their relevant research fields. Strain can be measured using mainly two methods (i.e., electrical strain sensors and optical strain sensors). Electrical strain sensors consist basically of strain gauges, piezo film, etc. In electrical strain sensors, the strain gauge is one of the oldest and reliable strain sensors which are available in different types (i.e., wire strain gauge, foil strain gauge, and semiconductor strain gauge). Piezofilm is also playing an important role in the field of strain measurement due to easy availability and less cost.

Behaviour of reinforcement in drop tower beam tests

Drop tower tests help to gain understanding about the general behaviour of reinforced concrete members under impact loading and to analyse strains and strain rates occurring within their reinforcement. For this purpose, beam and slab specimens are usually employed. The main advantage of beams compared to slabs is that they are less complex due to the almost two-dimensional instead of three-dimensional wave propagation within them. To investigate the steel strains and strain rates, ten impact tests on beam specimens with various impact energies were performed. The impactor sizes and velocities were varied. The reinforcement bars of the beams were instrumented with semiconductor strain gauges. The measured data suggest that the occurring strains in beam tests are independent of the loading velocity. The same was found for the strain rates. The reason is that higher impact energies mostly influence the concrete damage due to spalling on the impact-facing side which happens after the maximum strains occurred. The strains in the reinforcement bars generally result from the overall deflection because of the impact, the spreading of longitudinal waves in the horizontal direction, and the localized cracking of the concrete due to the formation of a punching cone.

Fingertip-Sized Pressure Sensor for Luer Taper of Three-Way Stopcock in Liquid Channel

We developed an easily attachable fingertip-sized pressure sensor (FSPS) for a three-way stopcock in a liquid channel of a heart–lung machine. The FSPS has a double-pipe structure with a semispherical soft film cap on the pointed end and a diaphragm semiconductor strain sensor on the other end. An enclosed space of variable volume covered with the soft film cap prevents the semiconductor strain sensor from coming into direct contact with blood, and the double-pipe structure decreases the strain on the strain sensor when inserting the FSPS into the female-fitting part of the luer taper. It is difficult to fabricate a very fine double-pipe structure by cutting or injection molding. Instead, we fabricated it by using a three-dimensional (3D) printer. Moreover, it is difficult to fabricate a semispherical soft film cap with a 3D printer, so we fabricated it with a resin casting method using silicone resin. Experiments on the FSPS using a variable pressure liquid channel showed that it is not affected by inserting it into the female-fitting part of the luer taper and that it can accurately measure pressure in a liquid channel within a pressure range from 0 to 100 kPa.