Istraživanje kontaktnih naprezanja između ojastučenja sjedala i korisnikova tijela

Design optimization of seat cushions is associated with the need to investigate their softness using, for this purpose, various kinds of loading pads. The aim of the investigation was: to determine seat cushion stiffness of a chair selected from a set of dining-room furniture, to determine values and distributions of contact strains on the seat surface caused by loading pad of different hardness, numerical calculation of contact strains between the seat cushion and the loading pad and to verify the results of these calculations with the results of laboratory experiments. The performed tests showed that the assessment of the seat cushion stiffness and the evaluation of contact stresses on their surface should be carried out using an equally stiff loading pad. In numerical calculations, polyurethane foams should be modeled as hyperfoam bodies of σ=f(ε) characteristics determined in an axial compression test. Contact stresses between the seat cushion and the user’s body should be reduced as a result of application of a frictionless connection of thin layers of polyurethane foams with foam forming the proper elastic layer of the seat.Optimizacija konstrukcije ojastučenja sjedala povezana je s potrebom istraživanja krutosti s gledišta različitih vrsta podložaka. Svrha opisanog istraživanja bila je odrediti krutost ojastučenja sjedala izabranoga iz asortimana namještaja za objedovanje, odrediti vrijednosti i raspodjelu deformacija površine ojastučenja sjedala s obzirom na podloške različite tvrdoće, numerički izračunati kontaktna naprezanja – deformacije između ojastučenja sjedala i podloška, te provjeriti rezultate dobivene laboratorijskim ispitivanjem. Provedena ispitivanja pokazuju da postizanje krutosti ojastučenja i procjena kontaktnih naprezanja na površini trebaju biti obavljeni korištenjem podložaka istovrsne tvrdoće. U numeričkom proračunu poliuretanske pjene trebaju biti modelirane kao potpuno upjenjena tijela kojima je čvrstoća funkcija naprezanja određena u aksijalnome kompresijskom testu σ=f(ε). Kontaktna naprezanja između ojastučenja sjedala i korisnikova tijela trebala bi biti smanjena zbog primjene spojeva koji ne uzrokuju trenje između tankih slojeva poliuretanske pjene i pjene koja tvori odgovarajući elastični sloj sjedala

Utjecaj oblika lijepljene površine na čvrstoću spoja rupe i čepa

Tenon joints are widely used in constructions of skeletal furniture and numerous laboratory experiments were conducted with the aim of determining the rigidity and strength of such joints. In industrial practice, the sloppily applied glue often covers only flat, rectangular planes of the tenon. In this situation, it can be intuitively predicted that such joints are characterised by low strength but the precise assessment of this difference, requires carrying out appropriate experiments and numerical calculations. Therefore, the aim of the performed investigations was: to define the strength of a tenon joint in the construction of a chair with a connecting piece, to determine the distribution of shear and normal stresses in the glue bond and to ascertain the infl uence of the glueline on this strength. The finite element mesh for the tenon joint was developed by using orthotropic, 20-node block elements, whereas the glue bond was modelled using isotropic elements 0.1 mm thick. The performed investigations showed that the shape of the glueline exerts a strong influence on the strength of the tenon joint. The pressure of the tenon on the mortise via the layer of the glue bond changes the form of deformations. Non-dilatational deformations, which generate shear stresses of values exceeding the ultimate strength, develop in rectangular bonds, whereas in superellipse bonds non-dilatational deformations clearly restrict the pressure of the tenon on the mortise and, by doing so, decrease considerably the level of dangerous shear stresses.Zaobljeni čepovi i rupe česti su elementi okvirnih konstrukcija namještaja s kojima su obavljeni brojni laboratorijski eksperimenti s ciljem određivanja krutosti i čvrstoće takvih spojeva. U industrijskoj praksi nepravilno izvedenim postupkom lijepljenja često je moguće pokrivati samo ravne pravokutne površine čepa. U takvom se slučaju može intuitivno predvidjeti da će takvi spojevi imati manju čvrstoću, no za preciznu potvrdu navedenih sumnji trebaju se provesti odgovarajući eksperimenti i računalne simulacije. Stoga je cilj ovog rada bio defi nirati čvrstoću spoja čepa i rupe u konstrukciji noge i poveznika stolice, odrediti posmična i normalna naprezanja u lijepljenom spoju i utvrditi utjecaj oblika lijepljene površine na čvrstoću. Mreža konačnih elemenata za spoj čepa i rupe bila je izvedena ortotropnim 20-čvornim elementima, pri čemu je sloj ljepila modeliran kao izotropni element debljine 0,1 mm. Provedena su istraživanja pokazala da oblik sloja ljepila ima velik utjecaj na čvrstoću spoja čepa i rupe. Pod utjecajem tlaka u sljubu čepa i rupe putem sloja ljepila mijenja se oblik deformacije. Nerastezljiva deformacija koja stvara posmična naprezanja čija vrijednost prelazi graničnu čvrstoću razvija se u pravokutnom obliku površine lijepljenog spoja pri čemu u zaobljenom dijelu lijepljenog spoja čepa i rupe nerastezljiva deformacija vidno smanjuje tlak kojim čep djeluje na rupu i čime se znatno smanjuje stupanj neželjenih posmičnih naprezanja

Numeričko modeliranje krutosti RTA namještaja s novim, izvana nevidljivim vezovima

The distribution of furniture sold in the form of flat packages requires the use of appropriate design solutions. These include joints, which need to facilitate self-assembly with no need to use tools. Such joints should be functional, aesthetically attractive, durable and safe to use. It was decided in this study to manufacture prototypes of innovative furniture joints and evaluate the quality of furniture assembled using these joints. For this purpose, the finite element method and the Abaqus program were used. Joints were modelled as objects made of polylactide (PLA). Surface to surface contact and assembly forces resulting from the construction of joints were introduced between the elements of the joint. The furniture case was subjected to torsional loads. The rigidity of furniture and stress distribution in joints were calculated. On the basis of numerical calculations, the joints were positively validated.Prodaja namještaja koji se isporučuje u obliku ravnih paketa zahtijeva primjenu odgovarajućih dizajnerskih rješenja. U takva se rješenje ubrajaju i vezovi koji trebaju olakšati samostalno sastavljanje namještaja bez primjene alata. Ti vezovi trebaju biti funkcionalni, estetski privlačni, izdržljivi i sigurni za upotrebu. Za ovo su istraživanje autori odlučili proizvesti prototipove inovativnih vezova namještaja te procijeniti kvalitetu namještaja sastavljenoga uz pomoć takvih vezova. Za tu je namjenu primijenjena metoda konačnih elemenata i program Abaqus. Vezovi su modelirani kao predmeti izrađeni od polilaktida (PLA). Između elemenata veza djeluju površinske i kontaktne sile koje nastaju konstrukcijom vezova. Korpus namještaja bio je podvrgnut torzijskim opterećenjima. Izračunana je krutost namještaja i raspodjela naprezanja u vezovima. Na temelju brojčanih izračuna vezovi su pozitivno ocijenjeni

Antropotehnička gledišta oblikovanja namještaja

A person having direct contact with a piece of furniture becomes part of an arrangement known as anthropotechnical system made up of an animate part (human body) and an inanimate part (technical facility – a piece of furniture). The aim of the research project was to present anthropotechnical aspects of furniture design for sitting and meal consumption. In particular, the author discussed the methodology of the assessment of ergonomics of a chair, a table and a chair + table set, where the assessment criteria were: anthropometric dimensions of the user, stiffness of seats and the value of contact strains on the seat surface.Osoba koja je u izravnom doticaju s namještajem postaje dio sustava poznatoga pod nazivom antropotehnički sustav. Njega čine pokretni dio (ljudsko tijelo) i nepokretni dio (tehnički objekt – određena vrsta namještaja). Cilj istraživanja bio je prikazati antropotehničko gledište projektiranja namještaja za sjedenje i objedovanje. U radu je posebna pozornost pridana metodologiji vrednovanja ergonomije stolice, sustava stola i stolice te grupe stolova, pri čemu su kriteriji vrednovanja bili antropometrijske dimenzije korisnika, krutost sjedala i vrijednost deformacije na površini sjedala

Vibrational spectra and normal coordinate analysis of CF 3 OF and CF 3 OCl

The IR spectra (1400 cm −1 to 160 cm −1 ) of the gases at ambient temperature and the Raman spectra (below 1400 cm −1 ) of the liquids near −196°C are reported for CF 3 OF and CF 3 OCl. All fundamentals are assigned under C s symmetry and the results of a normal coordinate analysis are presented. The assignments of Smardzewski and Fox are adopted with one exception for both CF 3 OF and CF 3 OCl: the CF 3 rock of A ″ symmetry is assigned near 430 cm −1 and the two bands between 200 cm −1 and 300 cm −1 are assigned to an A ′ fundamental, involving CF 3 rocking and COX bending and a Δ ν =2 transition in the CF 3 torsion. An extra band at 548 cm −1 in the Raman spectrum of liquid CF 3 COl near −196°C is assigned to a CF 3 OCl ⃛Cl 2 complex. The values of the force constants d (OX) for CF 3 OX molecules are suggested to be near those for X 2 O molecules. More than half the normal modes of A ′ symmetry show extensive mixing of symmetry coordinates. In some of these cases the symmetry coordinate for which the normal mode is named is the largest but not the dominant contributor to the potential energy distribution, while in others this symmetry coordinate is not even the largest contributor to the potential energy distribution. No normal modes of A ′ symmetry are present in which ν(CO), δ s (CF 3 ), δ(COX), or δ(CF 3 ) symmetry coordinates are dominant, and the mode conventionally labeled as v (CO) should be labeled as ν s (CF 3 ). For the remaining A ′ normal modes and all the A ″ normal modes, the symmetry coordinate for which the normal mode is named is dominant in the potential energy distribution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91176/1/1250090406_ftp.pd

Plastic deformation assessment of sawdust-rPET composites under bending load

Due to the scarcity of raw wood materials and the current state of the market's economic growth, the development of novel composite materials utilizing alternate raw material sources is crucial. Sawdust and waste polymers, such as empty bottles, are excellent sources of low-cost materials for making useful and cost-effective wood-plastic composites. This article's main goal is to ascertain how different filler contents and percentages, as well as two different types of polymer matrices, affect the mechanical properties of sawdust-reinforced composite in the plastic range of force-deflection diagram of bending test. Sawdust-plastic composites based on waste polyethylene terephthalate (PET) and biodegradable polymers were produced by the flat press method and prepared for mechanical testing. This study examined comprehensively the plastic range of the three-point bending test. The limit of proportionality (LOP), bending strength or modulus of rupture (MOR), plastic potential "PP", four tangent moduli as well as approximated plastic work "AW", total plastic work "BW" and the values of approximation error "ΔW" were measured using three-point bending test. The finite element method (FEM) analysis was also conducted to prepare a numerical model and compare its results with experimental results. According to the study's findings, the bending features of rPET-reinforced composites declined as the filler percentage increased. Among all the rPET-reinforced composites, the 40% sawdust filled composite had the best mechanical performance. When compared to the rPET matrix, the biodegradable polymer demonstrated superior mechanical performance in the plastic zone of the bending test. However, both the 40% sawdust-filled rPET composite and the biodegradable composites filled with 50% sawdust fulfilled the ANSI standard as an appropriate replacement for medium-density fiberboard (MDF) for interior applications.O

Metodologija dizajniranja novih spojeva za namještaj

Techniques for self-assembly and disassembly of furniture are predominant mainly in the group of cabinet furniture. The lack of new constructions of furniture joints affects the market development of skeletal furniture intended for self-assembly. These connections should have the following characteristics: be easy to assemble and disassemble, have a minimum number of components, meet aesthetic requirements and be externally invisible. The aim of the study was to develop a methodology for formulating the assumptions for designing a new connection of skeletal furniture. At the outset, the distinguished joint features were presented. Then, assessment criteria were formulated for each feature, with adequate numerical values. On this basis, specific joints and fittings for skeletal furniture were collected and divided into 84 groups. The prepared numerical values were used as the data for statistical analysis. In the first step of the analysis, relationships were characterized between the studied features using the Spearmans rank correlation. On the basis of statistical analysis, the correctness of the obtained classifi cation was confirmed. Based on the analysis of the characteristics of the cluster and Spearmans correlation coefficient values, there was no reason to highlight any qualities as a component of project assumptions. Cluster analysis pointed to differences between groups, as well as groups having similar features. Against this background, a clear design assumption was built.U skupini korpusnog namještaja uglavnom prevladavaju tehnička rješenja za samostalnu montažu i demontažu namještaja. Nedostatak novih konstrukcijskih spojeva za namještaj utječe na razvoj tržišta korpusnog namještaja namijenjenoga samostalnoj montaži. Konstrukcijski spojevi korpusnog namještaja trebali bi se moći lako sastaviti i rastaviti, imati minimalan broj komponenata, zadovoljiti estetske uvjete i biti izvana nevidljivi. Cilj istraživanja bio je razviti metodologiju za formuliranje pretpostavki za projektiranje novoga konstrukcijskog spoja za korpusni namještaj. Na početku rada prikazana su istaknuta obilježja pojedinih spojeva. Potom su za svako obilježje formulirani kriteriji vrednovanja, kojima su dodijeljene brojčane vrijednosti. Prikupljeni su i u 84 skupine grupirani različiti spojevi i elementi za spajanje korpusnog namještaja. Tako pripremljene numeričke vrijednosti uvrštene su kao podaci u statističke analize. U prvom koraku analize primjenom Spearmanove korelacije ranga određeni su odnosi između istraživanih obilježja. Na temelju statističke analize potvrđena je ispravnost dobivene klasifikacije. Na temelju klasterske analize obilježja i Spermanova koeficijenta korelacije pokazalo se da nema razloga za naglašavanje bilo kojeg obilježja kao sastavnog dijela projektne pretpostavke. Klasterska analiza označuje različitosti među skupinama, ali i povezuje skupine koje imaju zajednička obilježja. Na temelju dobivenih rezultata formulirane su jasne pretpostavke za dizajn novih spojeva korpusnog namještaja