Risk index calculator – a software tool for a quantitative assessment of risk of physical damage to objects vulnerable to climate variations
Arkadiusz Kupczak, Łukasz Lasyk, Łukasz Bratasz, Roman Kozłowski, Michał Łukomski
Museum environment – the plus/minus debate • It is acknowledged that the issue of collection and material environmental requirements is complex, and conservators/conservation scientists should actively seek to explain and unpack these complexities. • Risk management should be embedded in museum management processes. Environmental Guidelines - IIC – ICOM CC Declaration, 2014 (www.iiconservation.org)
The decision-maker needs to know the quantitative interrelation between the intensity of the hazard (climate fluctuations), the damage caused (cracks), and the cost of controlling the hazard.
Science can help. One approach has been the modelling of accurate ‘real-time’ moisture transport and the resulting strain and stress fields across the objects in response to temperature (T) and relative humidity (RH) variations.
Numerical simulations of the climate-induced dimensional response is based on finite element modelling (we are using COMSOL Multiphysics®)
Analysis of one time step Zmiana Input: Tparametrów and RH in the zewnętrznych surrounding–environment T i wilg. wzgl.
Calculation of moisture content across the object using data on the water vapour diffusion and sorption Calculation of the object response (deformation) using mechanical properties of the materials
Output: field of local strains
60
10.5
55
10.0
50
RH [%]
11.0
45
9.5
Experiment 9.0
40 35
o
8.5
Temperature [ C]
Deformation [mm]
Computer modelling can reproduce precisely the dimensional response of a real painting
30
Modelling
8.0
25 7.5 20 7.0
0
5
10
Time [days]
15
20
25
Comparing climates is difficult
Universal specifications for climate are just a starting point… (below, the safe range of 40 – 60% RH recommended by the Bizot Group, de facto 50% average RH ± 10%)
…a strain history of a specific object allows risk of damage to be better quantified (below, strain history experienced by the 0.4 mm thick gesso layer laid on a 10 mm panel; assumed strain at failure 0.2% Marion Mecklenburg’s failure criterion)
However, the finite element modelling: ‐ is time consuming ‐ requires large computational power ‐ requires specialized expertise and software ‐ therefore, cannot be easily used by conservation professionals/decision-makers We propose an alternative approach
HERIengine or HERIe
HERIe step 1 – decomposition of the RH data
One-year or multiyear RH data is decomposed into the set of elementary (sinusoidal ) fluctuations using the Fourier transform. RH variations (the church)
Elementary fluctuations Fourier Transform
HERIe step 2 – database of elementary strain variations The object Elementary RH variation
A freely responding panel covered with a gesso layer, imitating a panel painting Elementary strain variation
HERIe step 3 – superposition of elementary strains time = 0.5 sec
Strain history experienced by the 0.4 mm thick gesso layer laid on a 10 mm panel.
HERIe step 3 – superposition of elementary strains time = 0.5 sec time = 8 hours
Strain history experienced by the 0.4 mm thick gesso layer laid on a 10 mm panel.
Step 4 – risk of damage assessed using selected failure criteria
Failure criteria may come from laboratory studies, monitoring of original objects, collection observations (epidemiology studies). Above, the strain at failure assumed for the gesso is 0.2%.
Crack propagation [mm]
Step 4 – risk of damage assessed using selected failure criteria
a church a house museum
time [years]
The measurement of fatigue fracture of the gesso allows the risk of damage to be evaluated as crack propagation in time
Databases of elementary strain variations will be created for other typical heritage objects A restrained panel, imitating doors, sides of cabinets
wood A cylinder, imitating a sculpture
a sheet of parchment
library materials
Risk Index Calculator (HERIe + failure criteria) will be a web based tool freely available for conservation professionals and decision-makers - a user uploads one-year (or multiyear) temperature and RH microclimate data measured or simulated
Risk Index Calculator (HERIe + failure criteria) will be a web based tool freely available for conservation professionals and decision-makers - a user uploads one-year (or multiyear) temperature and RH microclimate data measured or simulated - defines types and characteristics of objects displayed or stored
Risk Index Calculator (HERIe + failure criteria) will be a web based tool freely available for conservation professionals and decision-makers - a user uploads one-year (or multiyear) temperature and RH microclimate data measured or simulated - defines types and characteristics of objects displayed or stored - calculates the strain histories using the HERIe module and selects failure criteria, to obtain risk indices.
Acknowledgements The team: A. Kupczak and R. Kozłowski - the Jerzy Haber Institute, Polish Academy of Sciences, Krakow, Poland Ł. Lasyk, Ukasz Technologies, Krakow and the National Museum in Krakow Ł. Bratasz, the National Museum in Krakow, now Institute for the Preservation of Cultural Heritage, Yale University M. Łukomski, the Getty Conservation Institute The development work has been made possible by a research grant from the National Centre for Research and Development Poland within the HERIVERDE Project (2013-2017).
First module of the HERIe will be available in September 2015 If you are interested in running test simulations, send me a message:
[email protected]
