Tests on facades of buildings
Fatigue stress, seismic stress
Our customer, a major research laboratory, required to certify conformity of glass curtain walls with modular components with European and Asian regulations.
We have under design the system able to place under stress curtain wall facades of 50 m2 with forces up to 200 kN, both on the side of the wall and orthogonally, able to simulate seismic phenomena to check both the structural resistance and the resistance to weather, rain and wind.
Tests on seismic joints
Fatigue stress, seismic stress
The seismic joints are resilient connection elements located within civil engineering structures and ensure resistance of the building to earthquake stresses.
For a major Italian world leading manufacturer Italsigma has manufactured the test machine able to perform the necessary tests for civil engineering approval. These are two-axle machines where the vertical-axle generates and maintains forces up to 30 MN, while the horizontal axle carries out travelling with strokes of a few centimetres and forces up to 3 MN. All this is to simulate the jerky and ondulatory movements that the seismic phenomenon generates.
Tests on gears
Fatigue tests, characterisation of materials
One of our customers wished to test the behaviour of a pair of gears in the latter’s laboratory simulating fatigue phenomena both in lubrication conditions and not. We have created the application by starting from a basic machine for mono-axial tests. The RT3 control system can interrupt the test at triggering of the defect and assess also the progression over time.
Tests on medical devices
Femoral implants, dental implants
The implants are medical devices that require certification by a notified Body. For certification is required the components characterisation of static and fatigue tests, able to establish and ensure the resistance at 5,000,000 cycles. Our customer wished to carry out the tests in its laboratory to ensure confidentiality on the selected technological solutions. Starting from the basic configuration of a static mono-axial machine we created special machines to place under stress, simultaneously under bending and twisting, several femoral implants or other medical devices.
Machine for dynamic tests up to 30 MN
A major University has commissioned us the creation of a 30 MN, 3,000 tons of force dynamic testing machine. This machine is used to test structural components. By using the TRIO SYSTEMS control system we planned the innovative technological solution to use as columns the hydraulic pistons thus ensuring movements in constant alignment. The machine can carry out both load control static and dynamic tests, as well as displacement and strain tests.
Tests on bicycle components
Fatigue tests on handlebars and frames
One of our customers, Italian leader in the manufacture of bicycle frames, decided to lighten its products by introducing components of carbon fibre and light alloys. To certify compliance of the components with the UNI EN 14766 Standard "Mountain bikes - Safety requirements and test methods" and UNI EN 14781 Standard "Racing bicycles - Safety requirements and test methods" has commissioned us the design and creation of special testing machines with special grips, which can reproduce on the individual components and on the frame the stresses on the frame required by the Standards.
Ultrasonic fatigue testing machine
90% of the mechanical components are subjected to fatigue, i.e. to repeated cyclic stresses. Fatigue, even though being originated from stresses lower than the yield strength of the material, can, anyhow, lead to breakage. Study of the materials fatigue behaviour is crucial for estimating the lifetime (duration) of the components and to ensure the manufacturer and the customer against undesired premature breakage.
The fatigue tests consist in placing under stress cyclically the specimen or the component.
To study the behaviour of the material, Wholer’s curve is set up with life of a definite number of cycles. In the Oil & Gas, Aerospace, Automotive and Railways fields the expected life is often higher than 10 million cycles, thereby leading to long waiting times for results and high costs.
Italsigma has developed an ultrasonic testing machine to generate high frequency stresses.
The benefits of using an ultrasonic fatigue machine are the following:
• Know the fatigue strength in a short time
It is an established practice to characterise the materials only through static tests, since the answer to the acceptance or not of the material must be available within a few days (in some cases a few hours) from its reception, so as to be able to proceed with the processing or assembly of the components.
Use of the Ultrasonic Machine allows, within half a day of testing, obtaining different results such as fatigue strength of the material and hence the quality guarantee in terms of length of life of the future products.
• Investigate beyond 10 million cycles
Currently, an increasing amount of components has a fatigue life expectancy that goes well beyond 107 cycles.
For example, components used in aircraft, automobiles, high speed trains, wind turbines, etc.
• Improve forecasting of the life expectancy of the product
• Use real data of fatigue resistance and avoid the use of probabilistic methods to predict the trend of Wholer’s graph beyond 107 cycles
Often the Wholer (SN) curves are represented up to 107 cycles, beyond which a horizontal asymptotic behaviour is taken by convention (for example Iron alloys) or not horizontal (for example light alloys) depending of the metallic alloy in question.
Implementation of a 30 MN calibration system
The Oil & Gas industry prescribes rigorous resistance tests on the components of the oil extraction plants.
The tests are to be carried out on finished components ("full scale test") that require special testing plants; in Italy there are excellent plants at the Materials Development Centre (MDC) S.p.A. Company (Soc. Centro Sviluppo Materiali S.p.A. (CSM)), a RINA subsidiary, which for years provide this type of service to industry leaders of this sector.
In recent years, the gradually increasing complexity of the oil extraction plants has led to request of resistance testing in accordance to specific international regulations on components increasingly larger, with diameters up to 20", by applying forces increasingly high up to 30MN. The plants, to carry out such tests, must be calibrated on a routine base and demonstrate complete traceability of the measurement system in accordance with the relevant international Standards. Given the large sizes and forces involved, until recently for calibration it was mandatory to use the North American market with limits on the force scale; at the request of the (MDC) (CSM), Italsigma has developed a modular calibration system used up to 30 MN, which has as reference dynamometer samples calibrated by INRIM. This paper describes the technical measures used and the experience carried out in the calibration activities.
Design, development and implementation of a test system for internal combustion engines bench stands
Even though having available the characteristics of the materials used for the manufacture of stands for internal combustion engines and having developed the design with calculation systems with respect to finished elements, the customer wished to validate experimentally what was implemented. As object of the validation it was identified that which its design system had indicated as critical, that is to say the bench stands. Italsigma was involved in designing a test system that can reproduce as faithfully as possible the service conditions, by using the production components. The system must be able to apply on the engine shaft a stress similar to that transmitted by the connecting rod as a result of the explosion of the fuel in the expansion chamber. The stress applied to the engine shaft at the connecting rod pins will drain off on the stand through the shaft bench pins and the relative supports on the stand.
These are the input data of the test design:
Maximum dynamic load: 300 kN
Frequency: 20-30 Hz
Dynamic load ratio: 0.05
Duration target: 5*106 cycles
From these data were deduced the following specifications for the bench test:
300 kN servo-hydraulic group with 1 mm @ 10 Hz stroke
Class 0.5 ISO 376300 kN dynamometer
210 bar @ 50 L/min (280 bar @ 40 L/min) silenced hydraulic source
20 kW thermal silenced water refrigeration unit
Up to 4 channels expandable electronic management channel
Development of a computerised machine for rotating flexing fatigue
The rotating flexing fatigue is one of the stresses that more closely reproduces the behaviour of a shaft or of an axle in the actual operation conditions: not by chance the qualification of railway axles requests rotating flexing fatigue tests.
The machines for rotating flexing fatigue are in use from many decades and substantially are very simple machines, mainly mechanical in nature, consisting by a rotating spindle on which is mounted the specimen and a load system that can generate a bending moment with various characteristics.
The ISO 1143 Standard Metallic materials - Rotating bar bending fatigue testing of 2010 specifies the different types of machine by characterising them depending on the type of bending moment which may apply.
The traditional machines are weight machines without any type of computerised feedback and control, often operating according to the diagram given above.
Italsigma has decided to develop a highly innovative machine that plans the control and the test management by Personal Computer.
The main advantages of this solution are:
• Monitoring of the bending moment and of the stress acting on the specimen
• Definition of test cycle sequences
• Continuous recording in controlled sizes
• Fracture control
• Intervention with interruption of the test at triggering time or when the customer defines it
• Evaluation of how the crack propagates from nucleation stage to final rupture
The machine belongs to the 4-point type bending, created with DC electric engine with variation of the rotation speed from 1,000 to 6,000 rev/min and a load system with electrical actuator. A dynamometer measures the actual load acting on the specimen and, in feedback through the computer, monitors and corrects the applied values.
The machine is designed to apply moments of up to 75 Nm and can be used with specimens having useful diameters from 6 to 10 mm.
The computer can handle one or more machines and allows the setting and the recording of the test parameters: the test data can be acquired and exported in excel file for any processing and reporting stage.
The effects of an earthquake on a reinforced concrete structure may be evaluated by placing the structure on a vibrating table. Often, however, the structures in the civil engineering field have such sizes that it is practically impossible to create adequate supports.
To allow full-scale elements testing, in recent decades Pseudo-dynamic (PSD) tests have been developed: these are particularly widespread especially for reinforced concrete structures in full scale and allow to assess the effects of the earthquake on the structure.
The test system substantially consists by a series of linear actuators, reaction frames, a computer and a hydraulic control unit.
In the computer are entered programmes that reproduce the stresses under which to subject the structure that can be of real type (such as recordings of previous earthquakes) or hypothetical (such as in the case of requirements envisaged in the design documents of the EC8 type).
The hydraulic actuators impose to the structure the defined displacements, while the dynamometers measure the reaction forces of the structure to the stresses.
Accelerogram planned for grounds of the B type in Euro Code 8
Example of accelerogram recorded during the Umbrian-Marche Provinces1997 earthquake
Accelerogramma previsto per i terreni di tipo B nell’Euro Codice 8
Italsigma and Trio Systems have developed a test system to create Pseudo-dynamic Tests on full-scale or reconfigured structures.
The computerised system for the control of the actuators exploits the feedback for the defined sizes and is able to apply the motion equations of the structure by resolving them in real time.
The system also allows measuring the reaction forces of the structure and of other mechanical sizes, thus providing the possibility of creating force-displacement diagrams and to record the variations over time. The acquisition of the test data also allows the comparison and any validation of the mathematical models of the structure behaviour.
The test system created by Italsigma and Trio Systems is modular, deployable in more than one step and customisable according to the most diverse customer requirements.
Example of multiple axles test system carried out for Messina University and usable also for Pseudo-dynamic Tests