Real-time computing

Real-time computing

In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...

 of cure

Curing (chemistry)

Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...

 monitoring is an essential component for the control of the manufacturing process of composite materials. The rationale for cure monitoring relies on the various physical or chemical properties that can be used to follow the transformation of an initially liquid thermoset resin

Resin

Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

 into its final rigid solid form (curing

Curing (chemistry)

Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...

). The relationship between the monitoring output and the requirements for feedback-loop control is the subject of extended research activities including considerations of the modelling of the cure reaction.

Techniques

• Dielectrometry: The technique of conventional dielectrometry carried out typically in a parallel plate configuration of the dielectric
  Dielectric
  A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
  
   sensor
  Sensor
  A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
  
   (Capacitance probe
  Capacitance probe
  Capacitance sensors use capacitance to measure the dielectric permittivity of a surrounding medium.The configuration is like the neutron probe where an access tube made of PVC is installed in the soil. The probe consists of sensing head at fixed depth...
  
  ), has the capability of monitoring the resin cure throughout the entire cycle, from the liquid to the rubber to the solid state and remains the only technique capable of monitoring phase separation in complex resin blends curing within a fibrous perform. The same attributes belong to the more recent development of the dielectric technique, namely microdielectrometry. Several versions of dielectric sensors are available commercially. The most suitable format for use in cure monitoring applications are the flat interdigital capacitive structures bearing a sensing grid on their surface. Depending on their design (specifically those on durable substrates) they have some reusability, while flexible substrate sensors can be used also in the bulk of the resin systems as embedded sensors.

• Optical fiber
  Optical fiber
  An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
  
   cure monitoring is performed by measuring
  • changes in the concentration of specific reactive resin species using spectroscopy
    Spectroscopy
    Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
    
     methods (FTIR & Raman)
  • changes in the refractive index
    Refractive index
    In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
    
     or fluorescence
    Fluorescence
    Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
    
     of the resin (optical property)
  • changes in internal resin strain
    Strain
    Strain can refer to:* Strain , variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes* Strain , a chemical stress of a molecule...
    
     (mechanical property) with the use of Fiber Bragg Grating
    Fiber Bragg grating
    A fiber Bragg grating is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by adding a periodic variation to the refractive index of the fiber core, which generates a...
    
     (FBG) sensors

• Ultrasonic cure monitoring methods based on relationships between changes in the characteristics of propagating ultrasound and the real-time mechanical properties of a component by measuring:
  • ultrasonic time of flight, both in through-transmission and pulse-echo modes
  • natural frequency using impact excitation and laser
    Laser
    A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
    
    -induced surface acoustic wave
    Acoustic wave
    Acoustic waves are a type of longitudinal waves that propagate by means of adiabatic compression and decompression. Longitudinal waves are waves that have the same direction of vibration as their direction of travel. Important quantities for describing acoustic waves are sound pressure, particle...
    
     velocity measurement.

• Thermal cure monitoring methods based on the amount of heat
  Heat
  In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
  
   produced during the thermoset cure reaction by measuring:
  • the amount of heat flux
    Heat flux
    Heat flux or thermal flux is the rate of heat energy transfer through a given surface. The SI derived unit of heat rate is joule per second, or watt. Heat flux is the heat rate per unit area. In SI units, heat flux is measured in W/m2]. Heat rate is a scalar quantity, while heat flux is a vectorial...
    
    per second through a given surface
  • the change in heat capacity for small resin quantities