NAME
    Tribology::Lubricant - Data type that represents a Lubricant class.

DESCRIPTION
    This class, given technical data based on lubricant TDS/PDS documents
    assists in calculation of various Rheologic characteristics of the
    lubricant. Such as:

    *   V-T behavior ("m()") using Ubbelohde-Walter equation

    *   Calculate viscosity at a given temperature ( "visc()" ) when any of
        two calibration points are known

    *   Calculate viscosity index using ASTM D2270's A and B procedures (
        "vi()" )

    *   Lookup L and H constants of the lubricant using ASTM D2270 Table and
        using linear interoplation whenever neccessary ( "LH()" )

SYNOPSIS
        require Tribology::Lubricant;

        # We already have viscosity at 40C and 100C. 
        my $lub = Tribology::Lubricant->new({
            label   => "Naphthenic spindle oil",
            visc40  => 30,
            visc100 => 100
        });

        # Viscosity @ 50C:
        my $visc50 = $lub->visc(50);

        # Viscosity index (VI)
        my $vi = $lub->vi;

        # Viscosity-temperature constant:
        my $vtc = $lub->vtc;

        # m-value, aka V-T behavior coefficient
        my $m = $lub->m;

        # To draw the V-T (hyperbolic) graph of this particular lubricant we can generate data-points, say, from -20 to +100:

        my @data_points;
        for my $T(-20..100) {
            push @data_points, [$T, $lub->visc($T)];
        }

        # Now you may pass @data_points to either GDGrap(Perl) or Highcharts(JS).

  new(\%attr)
    Constructor. Following attributes (all optional) can be passed:

    label
        Arbitrary label of the lubricant. Used in graph data or report
        tables, charts

    visc40, visc100
        Viscosity @ 40 and 100 degrees Celcius.

    vi  Viscosity index of the lubricant.

    density
        Specific gravity of the lubricant at a given temperature point. Must
        be passed a hashref of Temprature-Density values. Density must be in
        kg/cm3.

    IMPORTANT "visc40" and "visc100" are just convenience attributes, since
    they are most widely given in product TDSs. If you don't have
    calibration points at these temperatures IGNORE these attributes.
    Instead, create empty constructor, set the calibration values you
    already have using "visc()" method. Such as:

        my $lubricant = Tribology::Lubricant->new({label => "Hypothetical lubricant"});
        $lubricant->visc(50, 80);
        $lubricant->visc(100, 5.23);

  label($new_label)
    Returns and/or sets label of the lubricant

  visc($T, $cst)
    Given temperature ($T) in celcius returns kinematic viscosity in cst. If
    such value was not given to the constructor it attempts to calculate
    this number using Ubbelohde-Walter equation. For this to be possible at
    least two calibration points must be given to "new()" or two calibration
    points must be set using two-argument syntax of "visc()".

    If second argument is passed sets the viscosity point and returns the
    value $cst as is.

    # 1.10 (eni), bo'yi ( 2.27 )

  m()
    Heart of the Ubbelohde-Walter equation. This is the coeffient that
    characterises V-T behavior of oils. It's a double-logarithmic V-T graph
    slope. It requires at least two calibration points be present, or must
    be calculatable to work. Otherwise it throws error (croaks).

  LH()
    Returns L and H values for the given lubricant. For this method to work
    lubricant's viscosity @ 100C must be known or calculatable.

  vi()
    Returns viscosity index of the lubricant, if such is possible. Remember,
    for this to be possible calibration points at 40C and 100C must be
    available or calculatble. If it's impossible, it returns undef and
    writes a warning to STDERR. When checking for error you must check for
    "undef" at return.

  vtc()
    Returns VTC - viscosity-temperature constant used in Ubbelohde-Walter
    equation to better differentiate V-T behavior when the influence of
    temperature is low. This constant must be used to accurately (or
    properly) calculate "m". To calculate this value properly we need to
    have calibration points at 40C and 100C. If either of these points are
    missing "vtc()" defaults to 0.8.

  is_mineral
    Based on the "m" constant or "vi" attempts to guess if current instance
    represents a mineral oil.

INTERNALS
  __c2k($T)
    Given temperature in celcius converts it to Kelvin

  __k2c($T)
    Given temperature in Kelvin converts it to celcius

  __calibration_points($limit)
    Returns all known calibration points to the lubricant as array
    reference. If $limit is given limits the result set to that many points.
    The points are guaranteed to be in ascending order by temperature. All
    temperature points are converted to Kelvin, since that's what all
    internal formulas rely on.

  __vi_lt_100()
    Uses algorithm described in 5. Procedure A section of ASTM D2270. When
    you use "vi()" it invokes either method accordingly.

  __vi_gt_100()
    Uses algorithm described in 6. Procedure B section of ASTM D2270. When
    you use "vi()" it invokes either method accordingly.

SEE ALSO
    L<Lubricants and Lubrication|https://www.amazon.co.uk/Lubricants-Lubrication-Theo-Mang/dp/3527314970>, Second Edition by
    Wiley-VCH