Proceedings of the Institute of Acoustics

 

 

Protection of art gallery and museum collections from vibration

 

David Trevor-Jones¹, Sustainable Acoustics, Basingstoke, Hampshire, UK
Martin McNulty², Hoare Lea, Manchester, UK

 

ABSTRACT

 

Awareness that works in museum collections might be at risk of damage from exposure to vibration has existed in the art world at least since the 1930s. The acute risk is greatest when works are being moved. Early attempts at measurement and risk evaluation were focussed on works in transit. The assumption was that works at rest, exhibited or stored in gallery conditions, were no more vulnerable to vibration than the buildings housing them. That may hold true for conventional paintings, whatever their medium, age or even condition. Artefacts may be at greater risk. As practicable methods for monitoring emerged, especially during nearby construction, attention turned to the vulnerability of art objects more widely. Few verifiable cases of damage caused by exposure to vibration have been reported but the perception of risk has nonetheless increased. A necessarily precautionary approach has become ever more cautious, especially encouraged by the hypothesis that all objects are susceptible to accumulated exposure and eventual fatigue failure. Yet there is no numerical or experiential evidence to support that. A summary of a comprehensive literature review leads here to an attempt at numerical analysis of the risk, taking Michelangelo’s ‘David’ as a case study.

 

INTRODUCTION

 

A general awareness of the risk to works of art, meaning primarily oil paintings on canvas or timber, from the dynamic loading imposed by vibration seems to have existed at least since the 1930s. The earliest source found in the literature mentions the sacrifice of a de-accessioned ancient painting on a panel in poor condition for a shaking test to destruction but no primary report of that experiment has yet been found. It was generally assumed until relatively recently that art works were at highest risk in transit and that once safely housed in a gallery or museum, were at no more risk from imposed vibration or shock than the fabric of the building. Understandably, the impetus for deeper investigation came from exposure during handling and transport. The availability of battery-powered data loggers small enough to be packed into transport cases along with paintings (it seems that the early work in the field focussed solely on paintings) invigorated research. The first major international conference dedicated to the work in this field was held in London in 1991 [1].

 

Although the 1991 conference focussed on case studies of works in transit and discussions of protective measures in handling, packing and transporting works of art, it also provided a forum for important reports of fundamental research into the physical, chemical and mechanical behaviour of paintings. It was hoped that the evidence would inform numerically based, scientifically justified strategies for the protection of art works in transit, in storage and on display in museums and galleries. However, that is not what has happened and the purposes of this paper are to show how standards have developed and ultimately to present some new modelling results, compare them with present practice, and suggest restoration of a rational basis for standard-setting not least for vibration control in construction. Over-cautious standards may be resulting in significant time and cost, potentially constraining museum development. An extensive literature search has been undertaken but will not be presented in detail here.

 

FUNDAMENTAL PROPERTIES AND BEHAVIOUR OF PAINTINGS

 

An important body of work concerns the properties and mechanical behaviour of materials. Mecklenburg and Tumosa have led on the analysis of the properties of paint and underlayers. Their contributions to the 1991 Conference were significant, addressing the mechanical behaviour of paintings in response to the vibration and shock imposed during handling and transport [2] and on exposure to varying temperature and humidity [3]. Across the two papers they present a detailed investigation of the physical and chemical properties of paints and underlayers, concluding that “the findings of the study indicate that paintings have a substantial intrinsic dynamic strength and that within reasonable limits the objects are generally able to withstand considerable sustained vibration as well as rather serious impact.” Temperature and especially humidity cycling present a greater damage risk, as set out in [3] and by Michalski [4]. A rational basis for understanding the risks to paintings, and by implication the vibration limits or thresholds required to protect them from damage can come from the analysis of stresses associated with changes in temperature, relative humidity, shock, and vibration, and comparing them with the strengths of the artists’ materials [3]. Subsequent work e.g. by Young [5] reinforces that conclusion.

 

Michalski [4] concludes that “… experiments concerning vibration indicate that canvas paintings do not stretch enough to damage even the most fragile new gesso unless the canvas is subjected to unrealistically high levels. By this point, displacements are so large that indirect effects such as stretcher slap are the main problem, especially on large paintings.”

 

Alongside Michalski, Marcon has subjected model and real, de-accessioned works to drop tests and deliberate high amplitude excitation. Mecklenburg and Tumosa present computer models of stressed paintings that were compared with resultant crack patterns reported by Michalski and by Marcon showing close correspondence. Marcon’s experimental work provides a further powerful underpinning to understanding the fundamental properties and behaviours of paintings in different media on canvas and on wood.

 

Although that body of research evidence exists with more added since, particularly of numerical stress and strain analyses, subsequent practice in setting protective vibration standards for museums and galleries has seldom referred to it. In the next section the development of standard-setting to the present day is explored.

 

VIBRATION MANAGEMENT STANDARDS

 

A number of case studies have been reported from the UK, USA, Canada and Europe, mostly since 1999. For brevity here, the key contributions are summarised in tabular form. In Table 1 an overview is presented of the standards and thresholds set for a number of museums and galleries within or close to which construction works were undertaken. The reports in the literature refer to a range of metrics and unstated measurement parameters. Axial alignments go unmentioned. Magnitudes might be uni-axial or vector sums but are not identified as such. Impact shock is a key issue in handling and transit, and construction vibration is likely to be impulsive. Much early work was conducted with seismometers and results are reported in G. Stress is a function of displacement. However, velocity measurement is convenient and meaningful.

 

An attempt has been made to normalise the results in the summary tables presented below by converting results reported in G without frequency data into velocities for inter-study comparison. Velocity values, especially derived from shock values, might not completely represent the actual stress sustained by an object. Sinusoidal excitation has been assumed at 20Hz (from Smyth et al [11] and adopted by other authors in the field). The resultants are not explicitly ppvs but can be assumed to be for the purpose of general discussion.

 

Table 1: Synthesis of thresholds and limits

 

 

Notes

1. from unpublished report – authoritative source, confidentiality requested
2. from private correspondence – authoritative source, confidentiality requested

 

An interesting subset of results is available from a smaller number of studies in which baseline results were reported. Those are summarised in Table 2.

 

Table 2: Synthesis of reported baseline levels in museums and galleries

 

 

Reports of damage to objects in collections either as an observed or as an assumed consequence of vibration exposure are set out in Table 3.

 

Table 3: Synthesis of reported damage to objects in museums and galleries

 

 

A host of issues emerge from these syntheses. First, the early work on vulnerability had focussed on paintings, principally oil on canvas though other media and timber panels had been considered. The standards, though, do not generally refer specifically to paintings and oil paintings on canvas are notably absent from reports of damage. The term ‘art objects’ frequently appears in discussion of vibration standards in this field without deeper consideration of what that term could encompass in a particular institution and collection. Protecting museum collections can require consideration of anything from a fragile prehistoric ceramic to a steam engine and far else besides. An ‘art object’ can be almost anything. Assumptions are embedded in discussions, sometimes without explicit focus on and evaluation of the actual vulnerability of the collections concerned. The question arises of what the most likely or most threatening damage mechanism might be for a particular object that a vibration limit might prevent.

 

The development of damage prevention standards illustrated in Table 1 shows a downward trend over time but among the countless paintings, ‘art objects’ and museum artefacts protected by those standards there have been very few reports of actual damage indeed. The question begged is that of why the absence of reports of damage at higher vibration exposure thresholds led those advising institutions to lower them, even to levels lower than the probable baseline background arising from internal human activity and transport modes outside experienced every day in the building.

 

Is the absence of reported damage a testament to the efficacy of the vibration standards imposed or a clue that institutions are understandably reluctant to admit that damage has occurred in their collections? The greatest number of incidents in any one collection has been reported by Thickett [12] but that is unlikely to indicate a lack of curatorial care or insufficient caution on the part of the vibration management standards. In fact the single class of object most at risk of damage from vibration, widely mentioned from institutions around the world though without numerical analysis, is ancient Egyptian coffin lids adorned with paintings on gesso. The damage mechanism in that case is abrasion.

 

In general overview, the other potential damage mechanisms in respect of art and artefacts might be toppling, ‘walking’, falling and vibration-induced cracking. The last of these includes the special case of fatigue. There might also be sui generis object-specific risks, such as harmonic perturbation of suspended weights in antique pendulum clocks.

Toppling, ‘walking’ and falling are rather obvious risks. There are published formulae for calculating the critical toppling excitation magnitude for an object based on the height of its centre of gravity, its mass, footprint and other variables. It is instinctively obvious and true that a heavy object placed on top of a slender, light column will be more at risk than a pyramid placed on the floor.

 

The most insidious mechanism is ‘walking’. An object with a smooth base such as a ceramic or glass vase or a statue or clock displayed on a smooth shelf could be vulnerable. Even under quite low magnitude excitation such an object can be excited into gradual movement down-slope on even a slightly tilted surface. There are reports of such incidents occurring in museum collections in the literature and the author has encountered several anecdotally. The vulnerability of any particular object is a property of its mass, centre of gravity, the coefficient of friction between it and the surface on which it is displayed, the slope of that surface out of plumb and the direction of the

slope, and possibly other variables. It is probably impossible to prescribe a vibration limit to protect all items in any, let alone every, institution. The best practicable means of approach to eliminating or minimising the risk is to take preventive action on the receiving side. In a preventive campaign mounted by the Metropolitan Museum of Art in New York ahead of internal construction works governed by a curatorial desire not to take fragile items off display, objects judged to be vulnerable to vibration-induced walking were lifted and placed back on non-slip pads [11].

 

The mechanisms that standards are intended to address have received little explicit attention, but the properties of materials have been investigated and reported e.g. [2],[3],[5]. The link between those properties and protective numerical standards seems to be missing.

 

Empirical evidence suggests that paintings are not especially vulnerable to vibration-induced damage and the analytical research explains why. No reports of damage to paintings are listed in Table 3. Indeed, there is little objective evidence for vibration-induced damage in the form of degradation (other than by abrasion), cracking or breakage (other than by walking and falling) at all. The focus of research attention to mechanisms and damage consequences has fallen on fatigue failure. The risk was identified by Michalski [4], has been mentioned by others e.g. [9] but has been taken up as a dominant issue by Wei and collaborators.

In 2011 Wei et al [13] asserted that damage could be caused to art objects through fatigue failure on exposure to vibration at levels far below the strength of the materials would imply. Such damage was cumulative, resulting from vibration over the whole life of the object, leading eventually to cracking or dislodged paint, for example. Although accepting that there was no evidence to support the proposition or that the risk was real, the authors pleaded that a Wöhler S-N (Stress-Number) diagram should be developed for art objects. Hertzberg [14] was referenced for explanations of the mechanics and origin of the proposition. Fatigue dynamics is a complex field and Moore and Booth [15] offer a more basic, easily readable introduction to the subject.

 

Wei et al further develop the proposition in [10]. Many materials have a fatigue limit, a stress level that defines the amplitude of cyclic stress that can be applied to the material without causing failure. It can be a natural limit (the material really never fails) or determined by the user. The concept of ‘damage’ being a user-defined state is discussed later in this paper. The project in the work described in [10] was an attempt to construct an S-N diagram for paintings and another for other museum objects, incorporating everything from ceramics to sculptures in stone and in plastic in one lumped class. Data was collected from a number of European museums and galleries. Metrics presented a problem as the primary indicator of stress is amplitude whereas monitoring results have tended to be reported in terms of velocity or shock (acceleration or G).

 

The time axis also presents a conundrum when the period of exposure could have been hundreds or even thousands of years for archaeological finds but monitoring might cover the period of a construction project in the modern era. The more convincing results of the study are that as paintings and artefacts exhibited over many years in galleries and museums affected by baseline vibrations from road and rail traffic, visitor footfall and so on show no signs of damage, the baseline - taken as around 1mm/s - can be considered a safe value. Beyond that, the numbers of incidents of damage are small, those attributable to vibration exposure even smaller. The provisional S-N diagrams show that exposure of objects of all kinds to 2mm/s at less than 50Hz is unlikely to cause damage. That conclusion is somewhat speculative rather than established by the data.

 

Wei et al [8] report on the protection of objects in the Walker Art Gallery from damage by vibration during construction works at the Central Library, Liverpool. Monitoring thresholds defined for the works by others triggered an amber (in effect) warning at a threshold of 1.5mm/s ppv and a red alert at 3mm/s. Two incidents of damage are reported. One, of localised fragmentation on an amber cabinet, was attributed to vibration because the item had been on display for many years without damage; the other, of a fragment being dislodged from a timber sculpture, was attributed to failure of a brittle repair. A statistical analysis of the monitoring results was undertaken to determine whether a single alert or limit threshold could have been sufficient, citing the Palmgren-Miner rule (which states that fatigue failure results from continual accumulation of stress over time). The authors accepted that there is no data to support such an approach to risk management in a museum environment but interpreted their result as demonstrating support for it.

 

Marcon has addressed the fatigue proposition in [16]. Two conditions must be met for damage to occur: meeting or exceeding the critical stress threshold excess during each imposed vibration; and exposure to those conditions exceeding a cumulative time (cycle) threshold. While these conditions are an important issue in machinery and engineering structures they may not be important in museum objects. Marcon goes on to comment that acoustic excitation is similarly unlikely to pose a significant risk to artwork (as suggested by Wei et al 2011 [13]).

 

The present author has calculated a typical wind loading on a leaded light pane to test the proposition that windows at Hampton Court might have been damaged by rock music [17] and demonstrated that it massively exceeds the acoustic pressure from low frequency sound at 120dB. Harrison et al 2018 [18] represent a diametrically opposing view, counting among the threats to the National Gallery’s collection the cumulative effects of low-level vibration caused by sources including public events outside in Trafalgar Square.

 

The empirical and analytical evidence suggests that paintings in oil on canvas and on timber panels are not vulnerable to damage by typical levels of imposed vibration, even from external sources such as construction. Why, then, have the vibration level thresholds for protection of art, and in particular of oil paintings, been reducing over the past 20 years? The implication is that the art world is so acutely risk-averse that it really is seeking to reduce a near-zero risk to a zero risk (see e.g.[19]), or even in proposing protective standards below baseline levels, arguably beyond a zero risk.

 

RISK AND DAMAGE

 

Of course caution is understandable. The ethics of taking museum items and shaking them to see at what point they fail is unconscionable so precautionary standards are necessary. But the absence from the literature of many reports of any damage at all, and suggestion that damage is superficial where it has occurred, invites some sceptical consideration.

 

The suggestion by Wei et al [10] that all art objects are susceptible to fatigue failure is itself qualified by the warning that there is no numerical or observational evidence to support it. ‘Damage’, they declare, is what the curator determines it to mean. Ashley-Smith [20] discusses the concept of ‘damage’ in depth. It is not simply a crack or flaking of a surface. It has a philosophical dimension rooted in a judgement of ‘value’, itself a concept that requires interrogation. Ashley Smith points out that artefacts become susceptible to ‘damage’ as a consequence of being taken into museum collections and implies that if left to their own devices, would not accrue a ‘value’ or ‘damage’ in the same way. Damage is verging on an unavoidable condition. Exhibition of artefacts that illustrate and exemplify a culture is a moral imperative and the risk of exhibiting them, and resultant degradation, must therefore be accepted. Nothing lasts forever.

 

The concept of ‘damage’ is further developed by Henningsson 2018 [21] who observes that different stakeholders and professionals perceive value, risk, prevention and the meaning of long term management of change very differently. Allowable vibration levels are sought but ‘safe numbers’ in order to ensure that objects are not affected can be challenged. It is difficult to apply ‘safe numbers’ to the diversity of architecturally integrated materials and constructions in, for example, a historic church.

 

Yet the fatigue damage risk proposition seems to have seized the art world. There would be a real benefit to museums and galleries from a rational numerically, analytically-based risk assessment to back up careful, effective monitoring and management of vibration during construction. The objective in the work reported here has been to attempt to begin a process of evaluating the risk to artefacts of fatigue failure under rather low levels of vibration excitation.

 

AN ANALYTICAL MODEL

 

Michelangelo’s ‘David’ has been chosen for analysis because it is recognised around the world and its properties are understood. Pieraccini et al [22] have established its principal resonant modes by laser interferometry. It has been damaged during its history and its existing cracking and possible vulnerability to further damage have been investigated through modelling by Borri and Grazini [23].

 

A freely available 3D render of David has been converted into solid body form using ANSYS Spaceclaim Design Modeller (SCDM), then meshed and analysed in ANSYS 2021 R2. The dimensions and material properties of the statue have been derived from published information. The density and Young’s modulus of the marble have been adjusted to achieve a reasonable correspondence with the modal frequencies determined by Pieracini et al. The resulting mode shapes also correspond with previously published results. Confidence is thus provided in the correct deployment of the model for further static and dynamic analysis.

 

The base of the model is fixed and the static load under standard Earth gravity acceleration on the whole body added to find the location of the maximum vertical stress component. Its location in the leg/trunk region corresponds with the stress pattern obtained by Borri and Grazini. In the real statue the known, visible cracks are located in the region of maximum static stress and the object of the earlier study was to assist with a long-term conservation strategy by locating the stress points. The present study advances the analysis by examining the effect of adding a dynamic load.

 

The response of the model to an imposed dynamic stress over the static gravitational load has been investigated. The magnitude and frequency of a transient vibration pulse applied at the base were varied across the following ranges:

 

Forcing frequency Hz        4      8      20

Magnitude ppv mm/s         1      4       5

 

The resultant stress in the vertical axis at the point of the maximum on the statue was computed. The results are set out in Table 4 as absolute values.

 

Table 4: Absolute static + dynamic load stress at whole body max location, Mpa

 

 

The maximum shear stress of a sample of weathered marble, presumably originating in China, is given by Mingqing You [24] as 95.3MPa (it may differ in other marbles). The percentage of that limit represented by the maximum static and imposed dynamic loading stresses and by the dynamic stress alone are set out in Table 5.

 

Table 5: Total static + dynamic load stress and dynamic stress acting alone at whole body max location as percentage of maximum shear stress for marble

 

 

It is understood that a precautionary rule-of-thumb in engineering design to prevent fatigue failure is to limit the dynamic load on a structure to within 1% of its maximum shear stress at any critical point (private correspondence [25]).

 

The maximum dynamic load under vibration stress at the point of maximum stress on the statue is increased by 0.15% at 20Hz by a transient vibration pulse with a magnitude of 5mm/s ppv applied at the base.

 

CONCLUSIONS

 

Although the physical and dynamic properties of materials are available, limits and alert thresholds to protect gallery and museum collections from damage from vibration have been entirely based on precedent, incomplete understanding if the risks and in the absence of analysis of the stresses involved. The infinite variety of ‘art objects’, their material construction and their individual condition rules out the recommendation of general rules. Within a collection, though, it should be possible to identify the most vulnerable item or display of items and to base a rationale for protective standards around its object-specific vulnerability.

 

The calculations of static and dynamic stresses arising from imposed vibration excitation of Michelangelo’s David presented here offer a demonstration of principle. They suggest that the vibration magnitudes commonly arising from construction might not enhance fatigue failure risk. In the specific case of ‘David’ it ignores existing damage. However, the input data required for this kind of analysis are increasingly available. With reasonable assumptions concerning any that are not, it should be possible to develop analytical tools to estimate the sensitivities of key collection items to vibration and set collection and site-specific protective standards accordingly.

 

Some objects really are exceptional. The emerging evidence that paintings in pastel might be uniquely vulnerable to damage might encourage rigorous vibration limits, or alternatively might inform alternative curatorial decisions such as re-locating works. The preliminary results from ‘David’ do suggest that dynamic stress responses could lie further below fatigue limits than might be feared in the arts world and that severely restrictive limits, especially for other paintings, might be over-cautious.

 

The benefit of such an analytical approach would be two-fold. First, it would enhance confidence in curatorial decisions. Second, it might relieve some of the constraints on construction within and close to institutions, reducing the costs of those works by freeing up methods and reducing project durations.

 

Very importantly, the work reported here does not justify the widespread relaxation of restrictions on construction vibration affecting museums, galleries, art works in churches and in public and private buildings. Rather, it provides the basis for a more analytical approach to setting those restrictions and it might offer some guidance with respect to the extreme lower end of precautionary standard setting.

 

REFERENCES

 

1. ART IN TRANSIT Studies in the Transport of Paintings, hosted in London 9th–11th September 1991 by Canadian Conservation Institute of Communications Canada, Conservation Analytical Laboratory of the Smithsonian Institution, National Gallery of Art, Tate Gallery. Proceedings Edited by Marion F. Mecklenburg National Gallery of Art Washington ISBN 0-89468-163-X

2. Mecklenburg, M. F. and Tumosa, C. S. 1991. An introduction into the mechanical behavior of paintings under rapid loading conditions. Art in Transit. Studies in the Transport of Paintings. 09–11 September 1991. 137–172. Ed. Mecklenburg, M. F., National Gallery of Art, Washington

3. Mecklenburg, M. F. and Tumosa, C. S. 1991. Mechanical behavior of paintings subjected to changes in temperature and relative humidity. Art in Transit. Studies in the Transport of Paintings. 09–11 September 1991. 173–216. Ed. Mecklenburg, M. F., National Gallery of Art, Washington

4. Michalski, S. 1991. Paintings – Their response to temperature, relative humidity, shock, and vibration. Art in Transit. Studies in the Transport of Paintings. 09–11 September 1991. 223–248. Ed. Mecklenburg, M. F., National Gallery of Art, Washington

5. Young, C. R. T. (1996). Measurement of the biaxial tensile properties of paintings on canvas. PhD thesis, Imperial College, University of London

6. David Saunders, Mark Slattery and Ischa Mulder (1999). Building Work, Vibration, and the Permanent Collection. Conservation News, 68, 10–15

7. Watts, S., Berry, J., de Joia, A. and Philpott, F. (2002). In control or simply monitoring? The protection of museum collections from dust and vibration during building works. ICOM Committee for Conservation, 13th triennial meeting, Rio de Janeiro, 22–27 September 2002. Preprints 1, 108–115

8. Wei, W., Watts, S., Seddon, T., and Crombie, D. (2018). Protecting museum collections from vibrations due to construction: Vibration statistics, limits, flexibility and cooperation. Studies in Conservation, 63:sup1, 293–300

9. Johnson, A. P., Hannen, W. R., Zuccari, F. (2013). Vibration control during museum construction projects. J. American Institute of Conservation. 52(1), 30–47

10. Wei, W., Sauvage, L., and Wölk, J. (2014). Baseline limits for allowable vibrations for objects. ICOM-CC 16th Triennial Meeting Melbourne Preprints.

11. Smyth, A. W., Brewick, P., Greenbaum, R., Chatzis, M., Serotta, A., Stünkel, I. (2016). Vibration mitigation and monitoring: A case study of construction in a museum. J. American Institute of Conservation. 55(1), 32–55

12. Thickett, D. (2002). Vibration damage levels for museum objects. ICOM Committee for Conservation, 13th triennial meeting, Rio de Janeiro, 22–27 September 2002. Preprints 1, 90–107

13. Wei, W., Krumperman, N. and Delissen, N. (2011). Design of a vibration damping system for sculpture pedestals: an integral object-based approach. Proceedings of the ICOM-CC 16th Triennial Meeting, Lisbon, Portugal, 19–23 September 2011, Paper 1519

14. Hertzberg, R. W., Vinci, R. P. and Hertzberg, J. L. (2012). Deformation and Fracture Mechanics of Engineering Materials. 5th ed. Wiley

15. Moore, P. and Booth, G. (2014). The welding engineer's guide to fracture and fatigue. Woodhead Publishing

16. Marcon, P. (2018). Agents of Deterioration: Physical Forces. Canadian Conservation Institute Website

17. Randerson, J. (2007). Historic Buildings at Risk from Rock Concerts. The Guardian, 13 September 2007

18. Harrison, L., Higgitt, C. and Padfield, J. (2018). Finding common ground: the role of preventive conservation in response to contemporary audiences at the National Gallery, London. Studies in Conservation, 63:sup1

19. Kracht, K., Kletschkowski, T. (2017). A technical review on the problem of vibrating canvas. Part 1: Excitation and efforts of vibration reduction. Facta Universitatis: Series Mechanical Engineering. 15(1), 163–182

20. Ashley-Smith, J. (1999). Risk Assessment for Object Conservation. Butterworth-Heinemann

21. Henningsson, A. (2018). A model for vibration monitoring of immovable art in churches. Studies in Conservation, 63:sup1

22. Pieraccini, M., Betti, M., Forcellini, D., Dei, P., Bartoli, G. et al. (2017). Radar detection of pedestrian-induced vibrations on Michelangelo's David. PLoS ONE 12(4)

23. Borri, A. and Grazini, A. (2006). Diagnostic analysis of lesions and stability of Michelangelo's David. Journal of Cultural Heritage

24. You, M. (2011). Strength and damage of marble in ductile failure. Journal of Rock Mechanics and Geotechnical Engineering, 3(2), 161–166

25. Dr Lloyd Fletcher, Leverhulme Early Career Research Fellow and Lecturer, Aeronautical and Astronautical Engineering Department at the University of Southampton interviewed in June 2019

 

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¹ david@dtja.co.uk

² MartinMcNulty@hoarelea.com