Engineering design and validation of an innovative bionic CD rack

Carlos A. M. Versos, D. A. Coelho

Engineering design and validation of an innovative bionic CD rack

Carlos A. M. Versos1, Denis A. Coelho2

Abstract – This paper presents the engineering design analysis, of both a computational and analytical nature, that was performed in the development of a new bionic product, using an industrial engineering design approach. In the product engineering example, concerning an innovative CD rack, based on the principle of the spider web, elastic cable force creation by elongation is designed and validated, and the structure displacement and stress fields are simulated numerically.

Keywords: Product Design, Industrial Design Engineering, Computational Analysis

Glossary and NomenclatureCAD – Computer Aided DesignCD – Compact DiskDVD – Digital Video DiskPLA – Polylactic acidUV – Ultraviolet radiationm – massg – gravitational accelerationE – Young’s modulusl – lengthK – Elastic StiffnessA – Surface arear – radiusδ – elongationFH – horizontal component of forceFV – vertical component of forceP – WeightM Torque

I. IntroductionDesign methodologies are essential tools in the design process which provide pathways, goals and technical

guidelines for the development of products. Bionic design, a design methodology capable of enriching projects with gains in efficiency, aesthetics and sustainability and with a wide margin for improvement and with a whole world where inspiration can be reaped from, will certainly bring benefits to designers in the future development of their concepts and their research. As in Nature an environment in constant adaptation and renewal, where species evolve systematically and only the strongest survive and become adapted to the environment the planning and development of a product must also ensure an iterative nature of the process and constant reassessment of the design process (Versos and Coelho, 2013).

Several attempts to mimic biological systems behavior within new technology development have been reported (e.g. Sheeba et al., 2012; Gao and Luo, 2011; Shivakumar et al., 2010). Previous work by Versos and Coelho (2011a, 2011b, 2010) and by Coelho and Versos (2011, 2010) analyzed and compared several methods for guiding bionic design that were available in literature. These analyses, in addition to providing the basis of study for the development of the methodology that is aimed in this chapter, can support designers in the selection process of the bionic design method most appropriate to the problem at hand. Previous work emphasized the necessity of integrating validation activities in bionic design processes. The development and testing of improved methods that provide greater support to designers in the pursuit of activities leading to bionic solutions was the overarching of Versos and Coelho (2013). The need for

Working paper to appear in International Review of Information Technology


evaluation and validation during the development of bionic design projects enabling to measure product success in meeting efficiency targets and proposed requirements, was one of the evident missing features of previously existing methodologies for bionic design and which were met with the proposed methodology presented by Versos and Coelho (2013). Besides these aspects, the proposed method was also intended to support an iterative approach in conducting design projects in order to achieve optimal results and correct the detected deviations meeting the proposed objectives and needs. Implementation of the proposed method in practice (Versos and Coelho, 2013) aimed its validation and also confirmation of the gains introduced in projects that follow the methodology for the process of design with inspiration taken from Nature. This is explicit from the results obtained from the project, which in addition to validate the method, serves as a complement to present the method.

In this paper, the engineering design aspects of the development of two bionic products are presented. These were developed by Versos (2010), as part of his Master of Science Thesis in Industrial Design Engineering, supervised by the first author. In the product engineering example, concerning an innovative CD rack, based on the principle of the spider web, elastic cable force creation by elongation is designed and validated, and the structure displacement and stress fields are simulated numerically, in order to validate the achievement of design requirements set forth at the beginning of the design endeavor.

II. An innovative bionic CD rackA system for storing CDs and DVDs in their covers structured by elastic threads was delineated, allowing the

grasping of objects, in an attempt to dematerialize the archetype of ordinary shelves to result in a lighter solution, both visually and physically.

The system of elastic threads (warp) developed is visible in the Figure 21 and was disposed vertically for the purpose of guiding the objects in a fixed position to organize the storage and readability of the covers’ spines and arranged horizontally and obliquely for the purposes of gripping objects and for spatial organization.

Fig. 1 Arrangement of elastic threads of the shelving systems.The elastic threads are laid with pretensioning in holes in the structure itself, prepared for easy manual assembly or

replacement of the elastics if required.A "web" of elastic threads was used both in front and at the rear of structure in order to ensure the fixing of the

objects preventing them from falling.The structure of this solution was purposefully designed with a slope such as the positioning of the elastic threads

was both horizontal and oblique, so as to facilitate the reading of the spines of the objects to be placed in the system. The end result of this concept can be seen in Figure 2.

Fig. 2 Representing the final appearance of the bionic CD tower.



II.1. Materials used in the product concept

Given the requirement of reducing the environmental impact of the product, natural materials where intended for use, resorting to renewable and biodegradable materials, which were selected from literature.

The material selected for the production of structures and base of the CD rack is a biopolymer composite biodegradable PLA (polylactic acid) derived from renewable resources, as corn starch or canesugar, is Ingeo Biopolymer 3251, produced by NatureWorks (a pioneer in the production and marketing of polymers derived from annually renewable sources). The selection of this material was due to specific properties and resulting characteristics of the biopolymer, which is suitable for applications in injection molds, and is suitable for thin walls (reduced thicknesses) due to the high flowability of the resin. The material is opaque but it is also suitable for applications that require high gloss, UV resistance and rigidity. This material shows other characteristics appropriate to the concept of the project, such as its resistance to liquids.

For the production of the elastic strands, the material selected is a thermoplastic elastomer made from natural rubber and joining chitosan (35 CSNR 65). Thermoplastic elastomers show the properties of rubber to ease the processing of thermoplastics (Rao and Johns, 2007). Chitosan as a polysaccharide of natural origin (obtained from quitine, one of the most abundant natural polymers) has characteristics such as biodegradability, good mechanical strength, biocompatibility and has antimicrobial properties. According to Rao and Johns (2007), natural rubber is characterized by good elastic properties, good resilience and damping behavior. However, because of its chemical behavior it shows poor processing, hence the connection with the chitosan will improve this feature in the material, also increasing the modulus of elasticity of the material.

II.2. Iterative design of the pretension of the elastomers

In order to optimize the properties of the shape and geometry of the elements of the bionic CD rack, calculations were performed for the elastic tension forces of the horizontal or approximately horizontal and the vertical elastics, taking into account the properties of the materials selected. The diameter of the elastomers and the elongation of the initial stretch (assuming for both the differentiation between vertical and horizontal elastics) leading to the prestress concerned were considered as variables to define the design sought. The maximum vertical load to be borne by the horizontal elastics, was also determined in order to allow and make the simulation test activities for the validation of requirements, more complete and accurate.

Dimensions of the spine of a CD cover = 10 × 124 [mm]Dimensions of the area for storage of CD covers = 1080 × 300 [mm]Total number of CDs supported = 261Bulk CD single mass = 150grWeight per CD = m × g = 0.150 × 9.81 m/s2 = 1.4715 NMaximum load of CDs = 1.4715 × 261 = 384 N

Given that the product has 2 × 20 horizontal elastics, the vertical load supported by each of the horizontal elastics is then 9,6 N. These vertical loads are applied in the supports of the horizontal threads considering equitable distribution of the value to be applied on each side. Thus, one considers a load applied in the left and right end of each thread of 4,8 N corresponding to the portion of the load caused by the group of CDs that the thread supports. The following calculations are aimed at reaching the value of necessary pretensioning of the horizontal elastic threads.

For an initial strain of75% of the initial lengthDiameter (horizontalthreads) = 3 mmLength with 75%elongation = 36,3 cm =0,363 mMaterial: 3565 CsNr –Young’s modulus (E) =3,03 MPa (75%



elongation)Failure elongation =122,21%Failure stress = 3,37 MPa

Initial length (l) =0,363/1,75=0,2075mElastic Stiffness (K) =

Elongation (δ) =(elongated) l (initial) l

(prestressing) Force

Horizontalprestressing force ineach extremity of thehorizontal thread =15,72 N

For a thread horizontal diameter of 3 mm, an initial length of 207.5 mm is sufficient taking into account the mechanical properties of the selected material (CSNR 3565), specially its modulus of elasticity, a 75% elongation is high (3.03 MPa) close to the failure stress. There is still a margin of 47% of the initial length at failure. Given the horizontal load values obtained (15.72 N) and the available margin to stretch, it was not considered necessary to perform a new iteration. Thus, to occupy the width of the tower from one side to the other, which has a dimension of 363 mm on average, each elastic thread must be mounted with an initial strain of 75%, having a margin of about 40% to endure load, but with a modulus of elasticity much higher than it would be had there been no initial deformation. Since in this material the modulus of elasticity increases with the strain, and to this material as the breakdown stress is 3.37 MPa, the filaments of 3mm diameter will only breakdown if supporting a load equal to this stress multiplied by the area: 7.068 × 3.37 = 23.8 N

Thus, there remains about 7 N (2316 = 7 N) of capability to support elastic forces in each elastic cable. The additional deformation for this addition of 7 N corresponds to about 40% of the initial length, i.e. about 80 mm, considering the gap of 363 mm.

For calculation of the pretensioning forces of the vertical elastics the following iterations were performed.



For a predeformation of 75% of the initial length

Diameter (Elastics) = 3 mm

Length with elongation of 75% (bionic tower 1)= 125.5 cm = 1.255 m Length with elongation of 75% (Bionic Tower 2)= 107cm = 1.07 m

Material: 3565 CSNR Young's modulus (E) =3.03 MPa (elongation 75%)

(initial length)

Elastic Stiffness

K

K

Elongation (δ) = l(elongated) – l (initial)

δ

Prestressing Force

FV

FV

The forces for pretensioning the elasticized vertical cables for the bionic tower, calculated taking into account an elongation of 75% and 3 mm diameter have been found excessive and can cause weaknesses from a structural point of view when multiplied by the existing number of elastic cables. Thus, we proceeded to change the parameter of the initial elongated length of the stretch cables (from 75% to 50%) and the force of prestress resulting from the vertical elastic cables was calculated again.

The parameter change of initial elongation from 75% to 50% resulted in significant reduction of the tensile strength value of elastic vertical (9.86 N in the vertical elastics). However, in order to optimize this value appropriately and more



satisfactorily and, taking into account the mechanical properties of the material selected for manufacturing the structure of the towers, the vertical elastics diameter parameter was changed from 3 mm to 2 mm and calculations were remade.

After 3 iterations (1st iteration stretching 75%, diameter 3mm: FV ≈ 16 N; 2nd iteration stretching 50%, diameter 3mm: FV ≈ 10 N, 3rd iteration stretching 50%, diameter 2mm: FV ≈ 4 N) the parameters of elongation and diameter considered suitable to generate a vertical force on each vertical elastic that are considerable acceptable from a structural point of view were met. However, the computational simulation provided the validation test of this choice of parameters. This iterative analytical process reduced the number of iterations of the computer simulation and still enabled the designer to be in a position of control over the design parameters of the object.

II.3. Validation of the satisfaction of the requirement of storage with versatility

In order to demonstrate the satisfaction of requirements, tests were elaborated in order to carry out the analysis of the solutions created.

Thus, the requirement that relates to the versatility of storage with boxes of CDs, DVDs or books (1) elaborated a demonstration illustrating the versatility possible through 3D models obtained by modeling performed.

Fig. 3 Representation of dynamic storage possibilities of objects in the bionic CD tower.

Figure 3 demonstrates the versatility of storage boxes of CDs, DVDs or books allowed by the elastic properties, the orientation and spacing of the vertical and horizontal wires that make up the system of the web. The first diagram shows the possibility of image storage boxes of CDs and DVDs in boxes horizontal rows separated, for distinction of both digital media. The arrangement of the boxes of two brackets can also be mixed by placing boxes or CDs such as DVDs in the same horizontal row as a second possibility image storage exemplified. The elasticity of the wire also allows the storage of other objects with slightly different dimensions, such as books, visible storage scheme in the third image, never losing the parallel and vertical orientation of objects, regardless of the location where they are.

A demonstration of the strength of the structures of the towers for maximum storage through a tool for simulation and analysis of resistance testing efforts (COSMOSXpress, provided by SolidWorks software, version 2008) was also developed in the validation of this requirement.

For this finite element analysis (FEA), an advanced frame model was used with the loads made by the elastic cables at full capacity of the rack, placed in all the holes for the placement of the two ends of the elastic strands. At the location of the holes for the horizontal cables (or nearly horizontal) forces were inserted in the model based on the previously calculated values of the pretension exerted by the stretched wire (15.72 N) and the maximum load to be borne by each CD yarn (4.5 N). With regard to where holes are placed to secure the vertical elastic threads, a vertical force of 4.34 N in each hole meant for securing the pretensioned yarns was inserted.

Thus, in accordance with the material selected to construct the frame of the bionic tower (Ingeo Biopolymer 3251D), the following results were obtained, shown on Figure 4.



Fig. 4 Results of the distribution of von Mises equivalent stress under the loads applied.

As regards the distribution of the tension forces resulting from applied loads in the model, control up through Figure 26, the Von Mises equivalent stress to the area of greatest accumulated tension of 29 MPa. Taking into account the threshold failure stress of the bioelastic polymer selected (48 MPa) the safety factor for the maximum load test in an extreme situation is:

Safety factor

Figure 5 represents the distribution of the displacement in the frame of the tower resulting in the same scenario considered in the previous analysis.

Fig. 5 Results of the displacement distribution relative to the base, and considering the applied loads.

As can be seen in Figure 5 it is the upper portion of the frame that undergoes larger displacements, with a maximum of about 8 cm. This value is justified by the elastic properties of the biopolymer used, and the excessive load the model was submitted to in this analysis. Given this maximum displacement observed, and the safety factor that was calculated, leads to suggest that the bionic tower, before an extreme situation, is resistant to the conditions it is subjected to without compromising material properties.

A structural validation using the finite element method was conducted for the bionic tower. The FEM analysis carried to the tower bionic 2 resulted in a safety factor of 1.66.

II.4. Validation of the satisfaction of the requirement of greater stability facing a dynamic disturbance



The requirement of greater stability against dynamics disturbance in the face of conventional solution motivated calculation and analysis of disturbance threshold values (using a vector mechanical analysis) for a conventional CD shelf design using CAD solid modeling, and for the model resulting from bionic inspiration. In this analysis, limit values of disturbance were calculated for lateral stability (deemed more relevant due to the backrest of the shelves against the wall) and taking into account the maximum load capacity and the average load capacity of the designs.

Mass = 11,049 KgCentre of mass [cm]X = 20Y = 10,70Z = 56,09

Maximum capacity = 216 CDsMedium capacity = 108 CDsMass of 1 CD = 0.075 Kg

F = Maximum lateraldisturbance for stability

P = Weight of the tower +Weight of the maximum CDcapacityFor maximum capacity: For medium capacity:



Mass = 4,763 Kg

Mass center [cm]X = 27Y = 32,66Z = 42,63

Maximum capacity = 261CDsMedium capacity = 130 CDsMass of 1 CD = 0.075 Kg

F = Maximum lateraldisturbance for stability

P = Weight of the tower +Weight of the maximum CDcapacityFor maximum capacity For medium capacity



Table I summarizes the results obtained for both designs (conventional and bionic).

TABLE ICOMPARISON OF RESULTS FOR CONVENTIONAL AND BIONIC SOLUTION

Maximumdisturbancefor lateralstability

Conventionalsolution

Bionic solution

For maximumcapacity

49,96 N 49,59 N

For mediumcapacity

35,11 N 29,57 N

The results, summarized in Table I, point to similar tolerance and resistance to lateral disturbance by both solutions.The closeness of the values of maximum disturbance to the lateral stability of the conventional tower and the bionic

tower (the values of the latter being slightly lower than the values of the first) is justified by the fact that the bionic model is lightweight, compared to the conventional solution.

II.5. Validation of the satisfaction of the requirement of improved grasping of held objects

As regards the requirement of improved grasping of the major objects arranged compared to the conventional solution, the validation process is performed through calculations given by the specific horizontal elastic gripping when introducing a CD in the web, and by demonstration of the spacing between them

Mean spacing: 6 cm = 0,06 mCD height: 12,4 cm = 0,124 mLength (abreast of the tower): 0,35 mVertical displacement needed to accommodate a CD between two vertical elastic strings, spaced 0.032m apart.



hip = 0,1779 m

Additional elongation: 0,1779 – 0,175 = 0,0029 mδ(addit) = 0,0029 mδ(unloaded) = 0,363 – 0,2075 = 0,1555 mδ(addit + unladed) = 0,0029 + 0,1555 = 0,1584 m

F (addit + initial)H = = 16,35 NF (initial)H = 16,06 NF (addit)H = F (addit + initial)H – F (initial)H = 16,35 – 16,06 = 0,29 N

Percentage of Additional horizontal Force

Force applied to the frame by the elastic cable shown above

Since the analysis is made in a symmetric half, this value is multiplied by 4. It follows that the vertical holding force for each row of CDs will be around 11.77 N (2.94 N × 4).

Elastics have vertical alignment function, its pressure being negligible, but this is assisted by the friction between the surface of the CD cover and the surface of the elastic.

The additional horizontal force calculated results in the validation of the requirement for greater gripping of objects arranged in the tower. This is an indicative value which will depend on the actual configuration of the arrangement performed by the user.

Note that this additional horizontal force in the elastic cables that are horizontally disposed, being placed taking into account only the insertion of a CD into the middle of the web of elastics, leads to an increase of only 1.8% of the elastic tension set in the horizontal direction.

In a situation where there are many CDs and DVDs placed, in the web, a part of the elastic deformation leading to an increase in its tension and its deformation will eventually be transmitted in part to CDs and DVDs that are underneath and, ultimately, discharged directly into the base of the frame of the web.

Considering these aspects, this additional horizontal load value was discarded in finite element analysis. This analysis, which has led to a safety margin of 66%, absorbs very loosely around the 2% increase in horizontal load which was not given a significant nature.



III. ConclusionThe engineering validation steps of the bionic tower for storage of CDs and DVDs is considered successful, having

satisfied all requirements selected. As a result of the validation process followed, one can testify through this case study, the gains that the bionic approach has provided to the product, compared with a conventional model. Taking into account all these results, it is understood that the application of the method developed under the guidance of analyzing the problem to the solution (Versos and Coelho, 2013) is valid and can contribute to the development of optimized, efficient, sustainable and aesthetically pleasing products.

Prototyping would also be a future feature appropriate to proceed with the validation of projects developed in this work and future bionic design projects. A most effective visual assessment and the possibility of more complete testing would consolidate and witness more realistically the persuasive benefits of bionics.

AcknowledgementsParts of this work were developed within the scope of the M.Sc. Thesis of the second author, supervised by the first

author.

ReferencesD.A. Coelho, C.A.M. Versos (2010) An approach to validation of technological industrial design concepts with a bionic character,

Proceedings of the International Conference on Design and Product Development (ICDPD'10), Athens, Greece, 4045.

D.A. Coelho, C.A.M. Versos (2011) A comparative analysis of six bionic design methods, International Journal of Design Engineering 4 (2), 114131.

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V. Rao, J. Johns, (2008). Mechanical Properties of Thermoplastic Elastomeric Blends of Quitosano and Natural Rubber Latex. Journal of Applied Polymer Science, Wiley InterScience , Vol. 107, pp. 22172223 (2008).

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C.A.M. Versos, D.A. Coelho (2010) Iterative Design of a Novel Bionic CD Storage Shelf Demonstrating an Approach to Validation of Bionic Industrial Design Engineering Concepts, Proceedings of the International Conference on Design and Product Development (ICDPD'10), Athens, Greece, 4651.

C.A.M. Versos, D.A. Coelho (2011a) Biologically Inspired Design: Methods and Validation, in Industrial Design—New Frontiers (edited by Denis A. Coelho), Intech, 101120.

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Authors’ information1Technological Industrial Design Programme (Graduate), Dept. of Electromechancial Engineering, Universidade da Beira Interior, Covilhã, Portugal2Dept. of Electromechancial Engineering, Universidade da Beira Interior, Covilhã, Portugal.

Carlos A. M. Versos, M.Sc.Carlos A. M. Versos was born in 1987 in Covilhã, Portugal. In the academic year of 2005/2006, he entered the Industrial Design program at Beira Interior’s University. After graduation he continued pursuing the interest in this design field and concluded his master thesis in Technological Industrial Design at Beira Interior University with the theme of Bionic Design, with tutoring of Professor Denis Alves Coelho. His interest in nature, the background theme for his master's thesis led him to participate in projects to raise awareness and foster action for the preservation of forests trough education and volunteering programs. In his free time, Carlos Versos enjoys to draw and practicing sports to relax, such as cycling, karaté, kickboxing or jiu jitsu. Currently he is developing his PhD thesis, reflecting on the theme



of bionic design, while interning at a furniture design, manufacturing and sales multinationalcompany.

Denis A. Coelho, Ph.D.Denis A. Coelho has been responsible for the creation and development in the University of Beira Interior of an entirely new program of studies in Industrial Design (undergraduate studies leading to a Bachelor's degree) and Technological Industrial Design (Masters program). He has also designed and helped design postsecondary programs of studies including Multimedia product development, Ecommerce web applications and multimedia web applications. As a Mechanical Engineer with an Ergonomic Design and Production Management postgraduate education his research has focused in several areas. He has worked with car seat comfort (ergonomic design) and has also been interested in Management Systems in Small and Medium Enterprises, as well as providing a contribution to the advancement of ergonomic design methods. He has also participated and coordinated Multimedia design projects, focusing on the application of ergonomic guidelines at both the conceptual and application level. International exposure has included research performed in collaboration with Swedish and US universities, applied to the automotive and healthcare sectors.


Engineering design and validation of an innovative bionic CD rack

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