Studies of glued bamboo-wood composite for strength characteristics in the manufacture of aviation structural elements

doi:10.21203/rs.3.rs-2507370/v1

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Studies of glued bamboo-wood composite for strength characteristics in the manufacture of aviation structural elements

https://doi.org/10.21203/rs.3.rs-2507370/v1

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The goal of this study was the intention to demonstrate the expediency of utilization of bamboo composites in manufacturing of aircrafts. The research and testing of the material were conducted in the laboratories of the Institute of Aerospace Technolgies (IAT) of the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”. To determine the expediency of using bamboo composite, it is necessary to conduct tests of the material for external effects and analyse economic feasibility. The main advantages of such a material are its environmental friendliness and cheapness of both raw materials and processing.

This article is dedicated to analysing the results of the research on the mechanical characteristics and economic aspects. Bars of different sizes, different materials, and different degrees of processing were used for the analysis. The results of the testing conducted have showed that the strength characteristics of a bamboo composite are higher than that of the majority of wood species. At the same time, bamboo elements are lighter judging by weight characteristics. The undisputable advantage of their usage is a powerful and widespread structure of existing manufacturing which does not require creation of new processing machinery.

Physical sciences/Engineering/Aerospace engineering

Physical sciences/Materials science/Structural materials/Composites

bamboo

aircraft

composite

advantage

strength

expediency

Ecological concerns are quite relevant in the 21st century. Lawmakers all around the world are constantly bringing in new regulations to combat those issues, thus forcing the aviation industry to seek more climate friendly solutions. A lot has been done already to cut down on emissions and noise pollution, however the issue of materials used in aviation industry lies largely unaddressed. Production of aluminium is very energy consuming and costs a ton. On the other hand, it is recycles well. Usually people like to point out composite materials such as carbon as the material of the future. Although it has some advantages in comparison to aluminium such as being cheaper it is more energy consuming to produce, requires more complex machinery. The production and disposal of composite materials is also much more waste intensive. Concern about contribution of auto makers and aviation industry have led the European Union to ban composite materials from the landfills of its members with many countries outside of the EU are also following suit.

Price of personal aviation has not changed much despite the time that has passed since the first flight of the Wright Brothers, and stays a luxury for rich or enthusiasts alike, that have to invest a lot of money to create their own plane. Utilisation of bamboo composites can be a good push for light aviation thanks to it’s abundance and high strength characteristics relative to their weight. There is a lot of research going on in the field of materials and bamboo is no exception. However, very few works have been written on this topic in the aviation field. The novelty of the proposed study is that at the moment there is no definitive review with conclusions based on tests of bamboo-composite materials for strength for aviation use. The study allows us to verify that the use of bamboo composites exists among other modern materials, especially regarding environmental friendliness and sustainability. Currently, many studies target the study of bamboo composites, but most often choose large, whole pieces of bamboo: parts of trunks, strips of great thickness and width.

In the article “A Review on Bamboo Fiber Composites and its Applications” (N. Kaur, S. Saxena, H. Gaur, P. Goyal, International Conference on Infocom Technologies and Unmanned Systems 2017) authors describe the main principles behind the structure of bamboo and the way it is grown using a spreadsheet which goes into details about different varieties of bamboo, their differences and parameters.

They also focus on processing methods and talk about different ways of using bamboo in engineering and design solutions that have already been implemented and those that are still at the concept stage.

The paper "Evaluation and Comparison of Lightweight Bamboo Composite" (Andreas Lot, Michael Berving, Ralf Foerster 2016) deals with the environmental assessment of the structure. It also works on the possibilities of using bamboo plywood and how to form panels with a honeycomb grid from bamboo composites is also described. Special attention is paid to the lightness of the material while still having high strength. In their paper, “Flexural Properties of PVC/Bamboo Composites under Static and Dynamic Thermal Conditions: Effect of Composition and Water Absorption” (Shahril Anuar Bahari, Warren J. Grigsby, and Andreas Krause 2017) substantiate the effect of water absorption on polyvinyl chloride (PVC)/bamboo composites. Panels of this type retain their properties under the influence of moisture. After drying, it almost does not lose any of its properties. According to the source "Thermal and mechanical properties of bamboo fibre reinforced epoxy composites" (Kai Zhang, Fansin Wang, Wenyang Liang, Zhenqing Wang, Zhiwei Duan and Bin Yang 2018), it is proposed to improve the characteristics of bamboo fibre by treating it in NaOH solutions from 2–10%. Cementation at 6% is optimal for the production of bamboo fibre composites by the method of one tensile test. But at the same time, the results of their work show that the treatment does not provide significant advantages compared to ordinary dried bamboo when forming a composite. In the article "Application of sustainable bamboo-based composite reinforcement in structural concrete beams: design and evaluation" (Alireza Javadian, Ian F.S. Smith and Dirk E. Hebel 2020), the authors describe "bamboo processing processes”, they also give examples of characteristics of bamboo boards and Formation Beams of structurally loaded bamboo structures. Much attention is also paid to the processing of residues from the production of beams. The main purpose of the work is aimed at creating load-bearing elements in the construction of buildings where the cost of metal structures is very high. The paper “Sustainable Biocomposites for Aircraft Components” (Navin Jesu Arokiam, Mohammad Javaid and Nahid Saba 2019) discusses the use of Biocomposites in aircraft construction. They see the creation of a sheet design of panels and many cellular options as the main directions. The scope of application is mainly in the creation of interior and low-load elements. In their work, they give the mechanical characteristics of fibres: bamboo, banana, kenaf in comparison with artificial composites and metals. Bamboo has the best characteristics among all types of eco-composites. “A review of the tensile properties of bamboo fibre reinforced polymer composites” (Md Shah, A.U., Sultan, M.T.H., Jawaid, M., Cardona, F., and Abu Talib, A.R. 2016) also presents a comparative performance analysis for eco-composites. As a result, the high quality of bamboo composites can compete with conventional materials. Using bamboo fibres instead of synthetic fibres creates environmentally friendly products that reduce environmental concerns, especially in terms of energy consumption and solid waste recycling. The paper "Sustainable Material: An Experiment in Creating a Bamboo Composite through a Biological Bonding Mechanism" (I.F. Ridzqo, D. Susanto, T.H. Panjaitan and N. Putra 2020) describes how shredded fibres from bamboo production can be used to create panels for home furniture The main focus of the article is on the mechanism of end-to-end biological communication with the mycelium of mushrooms. The article "Differences in structure and strength between internodal and nodal parts of mozo bamboo" (Z. P. Shao L., Zhou Y. M., Liu Z., M. Wu, C. Arnaud 2010) discusses the biological formation of the bamboo stem and the fibre and nodal structure. Their results showed that in both planed and unplanned specimens, the knot had no reducing effect on flexural strength, longitudinal shear strength, and compressive strength. But the longitudinal tensile strength was significantly reduced.

The main purpose of the experiment is to check and determine the strength characteristics of bamboo. The study is divided into the following stages:

determining the breaking strength limit of segments of bamboo slats: clear internodes and with nodes, the amount of tension was determined by experimental methods;
determination of compressive strength;
bamboo bending test done by experimental methods;
research of glued bamboo lamellas;
comparison of glued bamboo beams with other materials used in aviation.

The basic objects of the study are bamboo slats, which are usually used as wallpaper elements (Table 1, Fig. 1).

Table 1. Geometrical characteristics of bamboo slats

Overall length	900 - 2800 mm
Height	1.9 - 2.1 mm
Width	5 - 24 mm

2.1. Typical Defects Of Bamboo Planks

The most widespread defects of bamboo lamellas are mechanical damage during processing: splits and checks (Fig. 2). Most of them are found near bamboo junctions. Scales occur less often and are most often observed at the ends of bamboo slats or in segments of internodes (Fig. 3).

Scales occur less often and most of them are observed on the ends of bamboo planks or segments with interconnections (Fig. 3).

The burnt wood is also very easily spotted during mechanical processing as well as the mold that penetrated the inner layers of bamboo (Fig. 4).

2.2. Experimental Methods

In tensile trials, the force applied to the sample at a given time and the corresponding elongation of the object are measured. For this purpose, breaking machines are equipped with special force-measuring devices — dynamometers — and deformation measuring devices. Methods of measuring deformations depend on the required accuracy of the results. It is easiest to determine the elongation of the sample by the movement of the movable grip, but the accuracy of measuring the deformation in this way is low, because the movement of the movable grip, in addition to the elongation of the working part of the sample with the initial length. related to the choice of gaps in the joints, etc. To measure deformations with maximum accuracy, special devices - strain gauges or extensometers - are used, which allow determining the elongation of only the working part of the sample.

2.3. Numerical Data Of Critical Stretching Strength Experiments On Bamboo Slats

A couple of light segments of bamboo which had no visible defects were chosen, the difference in length between these planks was also a millimetre or less. Herewith the structure of fibres for almost every sample was close to straight. The experiments for stretching were conducted for bamboo planks with δ = 2,1 mm: clear flat zone of internodes and of the nodes (Fig. 5).

Data received during the experiment for definitive stretching, demonstrated in Table 2 and on the graph 1.

Results of experiments show that most samples of bamboo without nodes have tensile strength between 100 and 110 MPa. Approximately 20% of all samples have reached tensile strength that is greater than 130 MPa and in less than 7% of objects the values of over 150MPa can be observed. The fibres of bamboo segments are directed straight, also the strips themselves lack even the slightest curvature. That is why it would be reasonable to avoid using planks that have nodes in their structure.

Most of the samples with nodes share the tensile strength close to 80MPa. Average deviation for samples without the nodes is -37,11%. For the greater strength of bamboo bars, they should be distributed in a way to prevent the overlapping of nodes along the full length or at least minimize the number of such overlaps.

2.4. Numerical Data For Compression Strength

Experiments on bamboo slats

Data received as the result of the experiment for compression strength are presented in the table number 3 and on the graph number 2.

During the compression trials, segments with nodes demonstrated better results, internodal samples on average withstood only − 26.45% lower stresses. Samples with clean voids are in the range from 50 to 70 MPa and have a more uniform distribution. Samples with nodes have an unstable distribution from 55 to 100 MPa. On average, the difference in samples was smaller during the compression experiments. The samples behaved more stably according to the parameter, only 20% with low values stand out from the others, and with high values less than 5% only the nodes of the samples.

Cross-cutting fibre strength structures for compression is much lower than it`s tensile strength. However, both parameters are important in aviation. All elements of the aircraft experience several forces at the same time. With many of the aforementioned forces varying depending on the current phase of the flight.

2.5.1 Numerical data from bamboo-plank bending trials.

Data received during the experiment for bending strength demonstrated in the Table 4 and graph 3.

The amount of stress bending bamboo slats can withstand equals 140 MPa on average. The distribution of internodal samples is more stable and is in the range from 115 to 150 MPa. Only 25% of the samples have a bending strength below 130 MPa. For the bamboo samples with nodes, a large instability in the distribution of values can be observed once again, with 10% of the samples having strengths above 155 MPa, while more than 25 percent of the samples have flexural strengths below 115 MPa.

2.5.2 Comparing The Ratios Of Results Of Tables 1–3

2.6. Glued Bamboo-rails

For most structures permanently durable elements such as spars are required. The production of such parts would be impossible without gluing the lamella together. In addition, gluing allows for the use of more bamboo samples and reduces production waste. In addition, it greatly simplifies the sorting of hearty bamboo.

At the next stage, samples were tested for tensile strength using a simple scarf connection (Fig. 6). At the same time, the most optimal angle at which the halves were glued was applied in the experiments. Mainly, the areas without knots were selected for gluing. The results are demonstrated in Table 5 and Graph 5.

For samples No. 3, 9, and 11, the failure occurred in the area of where the sample was attached. This indicates that the forces that exceed the normal threshold for tensile forces (perpendicular to the fibres) are present in the fastening of the sample. Samples No. 3, 9 and 11 are not connected by an adhesive seam.

Samples No. 1, 2 and 4 failed along the line of attachment of the clamp slips of the experimental machine. Which indicates the previous failure of fibres from mechanical damage to the structure. The samples were first tested and fixed directly in the machines. After several tests, the rest of the samples were fixed using duralumin spacers with glued sandpaper

Trials demonstrate that only glue joints with an angle tangent greater than 1/3 are applicable for use in aircraft bamboo structures. To a greater extent, the strength of the seam is also largely dependent on the glue used. “IZOL 3100 Mono” glue in particular has proven itself better than others.

Each time the results were unsatisfactory, there was either an additional stress or damage to the sample attachment or a defect in the adhesive bond.

Each bamboo sample is different and dispersion of them increases with the addition of different quality glues. Creating a notch before gluing and the processing of the seam also has an effect on the overall strength. Therefore, during production, it is necessary to clean the places of the adhesive seam with great diligence. Due to absorption properties of the bamboo, the amount of glue should be excessive on the seam. Seam quality control must also be conducted after the gluing of the strips.

2.7. Research Of Bamboo Girders

Before the creation of the girders themselves, bamboo should be checked for warping of the wood, especially for bending. It is much less common to encounter a twisted cup during the preliminary sorting of bamboo (Fig. 7).

When gluing bamboo beams, it is necessary to sort it so that the nodes and glue seams do not converge in one cut, because these places have a tendency to significantly weaken the structure.

Tests of bamboo girders made using the manufacturing technology have shown that their strength characteristics approach that of the small monolithic internodal segments of bamboo. And for large segments, it even shows a significant advantage due to the pre-processing and interleaving of internodes and segment nodes.

The breaking strength of bamboo girders lies between 80 and 90 MPa, 65–70 MPa in compression, and within 120–135 MPa in bending.

The loss of strength characteristics for glued bamboo girders over time and in adverse conditions is also higher than for wood, even without protective coatings. Typical sizes of glued bamboo bars (Fig. 8,9, Table 6).

Table 6. Geometrical characteristics of bamboo glued beam from slats.

Overall length	10–5000 + mm
Height	4–80 + mm
Width	5–60 + mm

Based on the results of the research, it can be said that the use of processed bamboo is appropriate in aviation. It has a fairly high strength-to-weight ratio. The density of bamboo wood is approximately 500 kg/m3, and the average specific strength reaches 130–240 kN•m/kg, which is 1.2 or more times higher than that of wood used in aviation. And this practically reaches steel and aluminium alloys. Experimental results showed that glued bamboo beams have better properties by more than 10% compared to monolithic bamboo segments presented in the authors' source: Juan Francisco Correal, Juliana Arbeláez (2010) “INFLUENCE OF AGE AND HEIGHT POSITION ON COLOMBIAN GUADUA ANGUSTIFOLIA BAMBOO MECHANICAL”PROPERTIES».

Low cost and ease of manufacture. High flexibility (graph. 7.) allows the production of many flexible elements: spars, frames, chassis supports and many other structural elements.

An inherent advantage is the absence of fatigue strength and the durability of the structure with almost no reduction in strength over time. After all, bamboo absorbs moisture poorly. Finally, bamboo is much more resistant to fire than wood and therefore offers much greater safety.

Bamboo load-bearing beams do not always lend themselves to restoration and repair, like wood, so the restoration of bamboo beams is dangerous and unacceptable for aviation. Therefore, the rule that scarfed joints used in the restoration of vintage aircraft are certified airworthy in most developed countries only if all such joints have an angle of at least 1:8 cannot be used. Experiments with repaired bamboo beams showed that the adhesive connection reduces the overall strength.

Price of the plane`s airframe is calculated using the following formula:

P_ag = P_mh × (T_lw + T_f + T_emp + T_lg + T_phs + T_aag) + P_pgm.

Where : P_mh – cost of man-hour (P_mh = 8$);

P_pgm – cost for airplane`s airframe materials;

T_lw, T_f, T_emp, T_lg, T_phs, T_aag – labour intensity for wing, fuselage, empennage, landing gear, pneumo- and hydraulic systems, assembly of the airplane`s airframe correspondently.

T_lw = K_pc.m.lw × G_lw/ρ⋅γ;

T_f = K_pc.m.f × G_f/ρ⋅γ;

T_emp = K_pc.m.emp×G_emp/ρ⋅γ;

T_lg = 0.2×G_lg;

T_phs = 9.5×G₀^0.46;

T_aag = 1.5×V_ag;

K_pc.m.element – processing complexity coefficient for materials in following piece of the craft for:

bamboo: wing-2, fuselage-6, empennage- 4;

aluminium: wing-14, fuselage- 12, empennage- 11;

fiberglass: wing- 18, fuselage- 16, empennage- 20;

carbon fiber: wing- 28, fuselage- 30, empennage- 20;

ρ_i – density i – index of the material;

γ_i – share of the material i – index of the material;

G₀ – empty plane mass.

Data for then designed plane:

made of bamboo: G₀ = 2421 kg, G_lw = 871 kg, G_f = 540 kg, G_emp = 90 kg, G_lg = 120 kg, G_ag=1621 kg;

made of aluminium: G₀ = 2391 kg, G_lw = 854 kg, G_f = 529 kg, G_emp = 88 kg, G_lg = 120 kg, G_ag=1591 kg;

made of fiberglass: G₀ = 2196 kg, G_lw = 740 kg, G_f = 459 kg, G_emp = 77 kg, G_lg = 120 kg, G_ag=1396 kg;

made of carbon fibers: G₀ = 2090 kg, G_lw = 653 kg, G_f = 443 kg, G_emp = 74 kg, G_lg = 120 kg, G_ag=1290 kg;

cost of man-hour is determined using the following formula:

P_mh=6×V_ag^0.15;

cost of the airplane`s airframe material:

P_pgm = P_mlw + P_mf + P_memp + P_mlg;

where: P_mlw, P_mf, P_memp, P_mlg – cost of the wing, fuselage, empennage, landing gear materials;

cost of constructional parts of the airplane`s airframe;

P_mpag=∑γ_i^Y × P_i^G/CMU_i;

P_mpag – cost of materials of a part of the airplane`s airframe;

where G_C – construction mass;

P_i – cost of 1kg of design;

С_fiberglass = 21$, С_alluminium = 9,5$, С_carbonFiber = 36$, С_bamboo = 1,8$, С_plywood = 2,1$;

γ_i – portion of the i-numbered material in the CMU_i (the average coefficient of material utilization in the structure).

Using the data of the tables of the methodical instruction and omitting detailed calculations, we get the following values of the cost of airplane`s airframe materials.

Table 7

Сost of fabrication and airframe materials.
(Type of Materials used in airplane`s airframe construction)	Material cost ($)	Airplane`s mass (kg)	Airplane`s cost ($)	Price per kilogram ($/kg)
Bamboo	11380	1621	82839	1.8
Aluminium	26098	1591	88825	9.5
Fiberglass	29753	1396	117994	21
Carbon fibre	33265	1290	165191	36

Price Analysis

Based on the results of the calculations (Table 7), we can see that the use of bamboo composite in aviation is expedient from the production efficiency standpoint. The price of bamboo composite is much lower than other popular materials. Aluminium for example is 5.28 times more expensive. The processing of such material does not require science-intensive methods, which in turn requires the use of extremely expensive equipment and highly qualified personnel.

The labour intensity of working with bamboo composite is very low, the manufacturing operations themselves are much simpler than the processing of other materials.

This article demonstrates that the use of glued bamboo beams and wood is very viable in the creation of highly ecological aircrafts. From the story presented in several sources, it becomes clear that this is a very wear-resistant material that does not burn well and does not absorb moisture well, even pipes are made of it. Defects and the way to sort bamboo are also described briefly, it is especially important in face of a great discrepancy in characteristics, which can be observed in different finished and semi-finished beam parts.

Significant advantages of bamboo composite are also the complete environmental friendliness of processing and waste disposal.

The choice of glue in the production of timber is of great importance, high-quality PVA in terms of price to quality ratio is the best option for the production of lamellas. And polyurethane for gluing lamellas and making of beams.

According to data acquired during trials, glued bamboo beams are 10 to 15 percent stronger than monolithic beams of the same weight and have performance parameters exceeding those of the aircraft-grade wood by more than 20 percent, albeit costing less.

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Tables 2 to 5 are available in the Supplementary Files section.

Graphs 1 to 7 are available in the Supplementary Files section.

There is NO Competing Interest.

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Studies of glued bamboo-wood composite for strength characteristics in the manufacture of aviation structural elements

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Abstract

Figures

1. Introduction

2. Methods And Results

2.1. Typical Defects Of Bamboo Planks

2.2. Experimental Methods

2.3. Numerical Data Of Critical Stretching Strength Experiments On Bamboo Slats

2.4. Numerical Data For Compression Strength

Experiments on bamboo slats

2.5.1 Numerical data from bamboo-plank bending trials.

2.5.2 Comparing The Ratios Of Results Of Tables 1–3

2.6. Glued Bamboo-rails

2.7. Research Of Bamboo Girders

3. Analysis And Discussion

4. Calculation Of The Airframe Price And Comparison With Alternative Materials

Price Analysis

Conclusion

References

tables

Graphs

Additional Declarations

Supplementary Files

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