NON DESTRUCTIVE TESTING
VISUAL TEST
Far from being trivial, visual testing (VT) should be applied in conjunction with other surface/volumetric methods and can provide an accurate examination of the condition of the component or double check any problems found during other analysis. Visual inspection can be applied to all industrial items.
General visual assessment
Of composite material components
in order to detect aesthetic anomalies and critical points in the production process, from the mould to the lamination phase and the curing cycle.
Of metal components
in order to detect corrosion anomalies and incorrect assembly according to UNI EN ISO standards.
ULTRASOUND TEST
Ultrasonic testing (UT) is applied through mechanical vibrations into a material and is able to detect volumetric discontinuities.
Detectable defects in composite materials
- Delamination between adjacent layers.
- Identification of the type of delamination.
- Presence of voids
- Disconnections at the interface between two different structures.
- Unbonding or voids between faces and internal core of a sandwich laminate
- Lack of bonding or voids of the inserts with composite-composite or composite-metal interface.
- Laminate thickness.
- Investigation of the laminate compaction obtained by the construction process.
- Presence of plastic or foreign materials in the laminate.
Detectable defects on metal parts
- General: inclusions, cracks, strains.
- Tubes and pipes: circumferential cracks and peeling on tubes and pipes.
- Flows: cavities, solid and gas inclusions, splits and cracks on flows
- Welds: dents, concavities, cracks, porosity, slag or gas inclusions, cavities, lack of vertex/heart penetration or lack of fusion.
PHASED-ARRAY
Thomas Young in 1801, demonstrated the undulatory nature of light. His experiment is based on a single source illuminating an opaque screen with two parallel slits of sufficiently small width compared to the wavelength of the incident light. In this way, by Huygens, the slits become two linear sources of coherent light that generate on a screen placed at a distance L an interference pattern formed by alternately dark and bright bands, depending on whether the interaction between the waves is in phase or out of phase. That means “phasing” can be used to control this interaction by time-shifting wave fronts originating from several sources (e.g. several elements housed in a single probe).
These sources, when stimulated separately using special models, can form a wavefront oriented in the desired direction, bringing some obvious advantages:
Software control of the ultrasonic beam
Greater adaptation for inspection of complex geometries
Different inspection angles through a single probe positioning via multiplexing mode
Wide variability of beam angle
Visual output under different views of the analysed area with A-Scan, S-Scan and C-Scan
THERMOGRAPHY
A non-destructive technique based on the acquisition of infrared, IR images, made possible by the fact that any object in an environment (above zero degrees Kelvin) emits radiation in the IR field. Due to the different specific parameters (such as thermal conductivity, specific heat) of each component that constitutes a given structure subjected to thermal stress, it is possible to determine a different temperature assumed by each of these components at an instant t. Because of this, thermography allows, for example, the detection of the presence of water and humidity, unevenness, delaminations and voids in the first layers of a composite laminate.
PENETRANT TESTING
PT is ideal for identifying discontinuities on the surface. It consists of the application and subsequent removal of a coloured liquid on the surface of the part to be inspected. After removal, the liquid will only persist in any discontinuity and reveal itself in the final inspection phase. The main constraint of this analysis is the need for a non-porous surface. In this case there will be diffuse absorption of the liquid, making it impossible to detect the real discontinuities on the component.
R&D
NOA will always focus on innovation and technological research, which is why we offer technical support services to our customers.
DSC
The differential Scanning Calorimetry can be applied on polymers, such as resins (epoxy, vinylesters or polyesters), which are widely used as matrix on composites. In these cases, a curing process is applied so that the monomers cross-link to form a macromolecular structure. The control of this process becomes particularly important structural parts that must meet precise design requirements. DSC analysis can help to understand and improve this process measuring the difference of the heat absorbed or released by a sample (compared to reference) during its controlled heating or cooling process.
Information obtained:
Glass transition temperature
Melting point
Enthalpy of transition and polymerisation of the resin
Crystallisation percentage
FIBRE TO RESIN RATIO
The fibre, resin and voids ratio on composites laminates is determined burning the laminate matrix without damaging the fibres. The result will lead to the calculation of the fibre and resin percentages by mass and volume. With this data it will be possible to calculate the percentage of voids by volume through the UT method.
DENSITY
Very often, mechanical behaviours of a finished product do not match design requirements. This is why “safety factors” are used to protect a range of variables. Variation in density could have a very negative effect on the correspondence between the “designed component” and the “manufactured component”. Determining the density of a material can give information on its homogeneity and consequently on its mechanical properties.
PULL-OFF
It tests the adhesion strength of a substrate of a local portion of the surface by applying a tensile stress normal to the test surface itself. We obtained a tension determined by the instant of failure of the weakest interface under test, be it an adhesive or cohesive fracture.
Results:
Determination of the failure mode
Determination of the strength between the coating and the rigid substrate (metal, GRP, wood)
Determination of skin-core tensile strength in sandwich panels
MOISTURE ANALYSIS AND OSMOSIS
The moisture content of structural elements (such as hulls and other structures) and/or aesthetics elements, is closely related to their deformation and degradation phenomena. The same anomalies within a material can be hollow or sometimes full of liquid.
Moisture has a significant influence on the results of physical and mechanical characterisation tests on the material. This analysis becomes important if assisted by visual, thermographic and ultrasonic investigations thus have a more complete picture of the state of conservation of the part.
VACUUM-BOX TEST
This is used to detect leaks in a confined environment that cannot be directly pressurised. This is achieved by applying a vacuum to a localised area of the surface, thus creating a pressure differential between the environment inside and outside that surface.
This type of investigation is ideal for:
Low-pressure testing where a pressure test would be overloading and could lead to the collapse of the structure
Tank bottoms that cannot be pressurised
Industrial plant leaks
Weld investigations