Effect of loading type on the fatigue strength of symmetric and asymmetric welded joints made of ultra high strength steel

In this study, finite element analyses and experimental tests are carried out in order to investigate the effect of loading type and symmetry on the fatigue strength of three different non-load carrying welded joints. The current codes and recommendations do not give explicit instructions how to consider degree of bending in loading and the effect of symmetry in the fatigue assessment of welded joints. The fatigue assessment is done by using effective notch stress method and linear elastic fracture mechanics. Transverse attachment and cover plate joints are analyzed by using 2D plane strain element models in FEMAP/NxNastran and Franc2D software and longitudinal gusset case is analyzed by using solid element models in Abaqus and Abaqus/XFEM software. By means of the evaluated effective notch stress range and stress intensity factor range, the nominal fatigue strength is assessed. Experimental tests consist of the fatigue tests of transverse attachment joints with total amount of 12 specimens. In the tests, the effect of both loading type and symmetry on the fatigue strength is studied. Finite element analyses showed that the fatigue strength of asymmetric joint is higher in tensile loading and the fatigue strength of symmetric joint is higher in bending loading in terms of nominal and hot spot stress methods. Linear elastic fracture mechanics indicated that bending reduces stress intensity factors when the crack size is relatively large since the normal stress decreases at the crack tip due to the stress gradient. Under tensile loading, experimental tests corresponded with finite element analyzes. Still, the fatigue tested joints subjected to bending showed the bending increased the fatigue strength of non-load carrying welded joints and the fatigue test results did not fully agree with the fatigue assessment. According to the results, it can be concluded that in tensile loading, the symmetry of joint distinctly affects on the fatigue strength. The fatigue life assessment of bending loaded joints is challenging since it depends on whether the crack initiation or propagation is predominant.

Tuotesuunnittelu direktiiviperustaisesti

Onnistuneen tuotekehitysprojektin läpivieminen vaatii huolellisen alkusuunnittelun ennen varsinaista tuotteen kehityksen aloitusta. Projektin läpiviemiseksi esitetään usein malleja joissa tuotekehitysprojektissa edetään yksi vaihe kerrallaan ja siirrytään seuraavaan vasta, kun edellinen on valmis. Tämän perinteisen mallin rinnalle on tullut DFMA-suunnittelu, jossa murretaan kommunikaatiomuuri suunnittelun ja valmistuksen väliltä ja useita vaiheita tehdään samanaikaisesta. Näin saadaan valmistus- ja kokoonpanoystävällisiä tuotteita, joilla tuotteesta saatava kate voidaan maksimoida samalla kun tuotteen laatua saadaan parannettua. Teknisen kehityksen lisäksi on tuotekehitysprosessissa erottamattomana osana direktiivien asettamien vaatimusten huomioon ottaminen. Jo lähes kaikissa tuotteissa on oltava CE-merkintä. CE-merkinnällä tuotteen valmistaja ottaa täyden vastuun siitä, että tuote täyttää sitä koskevien direktiivien asettamat vaatimukset vaatimustenmukaisuudesta. Direktiivien asettamat vaatimukset on hyvä tiedostaa jo tuotteen suunnittelun alkuvaiheista lähtien, jotta nämä osataan ottaa heti huomioon ja jälkikäteen tehtäviltä muutoksilta vältytään. Teknisten ratkaisujen lisäksi tuotteen dokumentoinnilla on suuri rooli vaatimustenmukaisuuden täyttämisessä. Tuotteesta tulee koota tekninen tiedosto, joka sisältää kaikki tarpeelliset dokumentit, joilla tuotteen vaatimustenmukaisuus voidaan todeta. Teknisen tiedoston vaatimukset on hyvä tiedostaa jo suunnittelun alusta lähtien, jotta tarvittavat dokumentit osataan kerätä projektin aikana tekniseen tiedostoon. Tässä työssä kehitettiin peltier-jäähdytin, jollaiselle asiakkailta saadun palautteen perusteella oli markkinoilla tarve. Jäähdyttimen suunnittelussa käytettiin DFMA:n keinoja yksinkertaistamaan kokoonpanoa. Jäähdyttimelle tehtiin vaatimustenmukaisuustarkastelu, missä tarkasteltiin peltier-jäähdytintä koskevien direktiivien asettamia vaatimuksia ja mitä asioita näiden vaatimusten täyttämiseksi tuli huomioida.

Home Made Cars: An insight on Consumer Ethnocentrism – Case Saab

Saab outstands in the history of the Finnish car manufacturing. This is not only due to that these cars have been manufactured in Finland more than other passenger vehicles altogether. Finns also have a special emotional attachment to the “Finnish Saabs”. Findings from previous studies show that consumers connect cars well to the origin of the brand (COB). They are however rarely aware of the Country of Manufacturing (COM). Domestic brands are often popular in the COB, but research from situations in which the domestic origin is limited to the COM is rare. The case of this study is a phenomenon, in which the products origin is two dimensional and divided into domestic COM and foreign COB. The aim is to understand the phenomenon’s effect on consumer behavior. The research problem is approached with two sub questions: • Which country do consumers perceive as the origin country of the car? • What is the role of this origin in the consumers’ product perception and purchasing decision of the car? The theoretical framework of this study applies previous findings of two areas of interest: Country of Origin effect and Consumer Ethnocentrism. This is followed by feasibility studies that present and discuss the history and current state of Finnish car manufacturing. Based on the findings of earlier stages of the study, the role of the domestic COM on consumer behavior is presumed high. This expectation is confirmed by the experts and also by the first consumer respondent, who states domestic origin having been the main motivation to his car choice. All further consumer respondents do however not connect Saab to the home country, but discuss it as a Nordic car. This unexpected finding means that they do not perceive the origin to be neither the COM nor COB, but a geographical area that includes both countries. In other words, consumers have widened their in-group in a way that is in this thesis explained with reference group theory. The consumers’ perceived origin of the car is in this research found to be an important factor to the consumers’ product perception and purchasing decision. Being fit for the yields of the local environment is discovered to have been the most important factor to Finnish consumers purchasing choice of a Saab and the Nordic origin has been an indicator of this fit to them.