Diss. Luleå : Luleå tekniska univ., 2007. / Härtill 6 uppsatser.

Licentiatavhandling (sammanfattning) Luleå : Luleå tekniska univ., 2002. / Härtill 3 uppsatser.

Diss. (sammanfattning) Linköping : Univ., 2002. / Härtill 4 uppsatser.

Lic.-avh. (sammanfattning) Luleå : Luleå tekniska universitet, 2009. / Härtill 3 uppsatser.

Lic.-avh. (sammanfattning) Luleå : Luleå tekniska universitet, 2009. / Härtill 3 uppsatser.

This bachelor thesis in mechanical engineering was performed during the spring2015 in collaboration with Composite Consulting Group in Laholm. TheComposites Consulting Group works mainly with design and details of differentcomposite projects, their main area is FE-calculations, 3D-modelling andmechanical tests with composite materials.The aim of this bachelor thesis was to simplify the calculation process of solidmechanics for sandwich panels by simulation with computer software. The goalwas to decrease the time for the design and calculation process of the constructionand the cost of the practical tests. Our task was to build a static three dimensionalmodel with the computer software Abaqus, where the result should correspondwith the practical pressure tests in laboratory.The project started with collection of material data from Composites ConsultingGroup and by learning the software Abaqus, simultaneously a specification wasdeveloped in corporation with the company. Later on, a static wheel pressuremodel in the software Abaqus was produced which simulated the behavior of thesandwich panel during static wheel-pressure by a pallet truck. The results from thewheel-pressure model were verified with the practical tests.The project led to a static three dimensional wheel- contact model with thesoftware Abaqus to calculate complex wheel-contact problems on sandwichpanels. The wheel-contact model corresponded to the practical test results. Thecontact model with Abaqus enabled faster and more efficient design anddevelopment process of new sandwich panels. It also provided better analysis ofthe sandwich panels’ behavior during wheel- contact loading.

Diss. Luleå : Luleå tekniska univ., 2002.

Diss. Luleå : Luleå tekniska univ., 2002.

In recent years, steel components manufactured through additive manufacturing have increased their popularity and commercial importance and carbon fiber reinforced polymers are widely used in today’s society. Yet there is no composite material combining the properties of steel and carbon fibers. This thesis work is a part of the World Class Material-project at Swerim AB where different methods for manufacturing a steel matrix carbon fiber composite are researched upon. Two methods for additive manufacturing: selective laser melting and electron beam melting were used to evaluate the possibility of creating a steel matrix carbon fiber composite. The experiment with electron beam melting was conducted without powder and the two selective laser melting experiments were conducted with powder using fibers with organic and metal coating respectively. The main aspect evaluated was the survival of carbon fibers during processing. The results showed no intact carbon fibers after processing organically sized fibers in either of the processes. In the selective laser melting experiment with organic coating, big voids were found where the fiber bundles had been placed, showing no infiltration of powder or molten metal into the bundle prior to fiber breakdown. The metal-coated fibers survived partially but showed poor infiltration of matrix material into the carbon fiber bundle. The methods used in this report were not found suitable for the manufacturing of steel matrix carbon fiber composites. / De senaste åren har additiv tillverkning av stålkomponenter blivit alltmer populärt och kolfiberarmerade polymerer används i stor utsträckning i dagens samhälle. Trots det finns det i nuläget inget kompositmaterial som kombinerar stål och kolfiber. Detta kandidatexamensarbete har varit en del av World Class Material-projektet på Swerim AB, där olika metoder för tillverkning av en kolfiberkomposit med stålmatris undersöks. Två additiva tillverkningsmetoder, selective laser melting (SLM) och electron beam melting (EBM), användes för att utvärdera möjligheten att med dessa tillverka en stål-och kolfiberkomposit. Testet i EBM genomfördes utan pulver och i testerna SLM med pulver där fibrerna i ena försöket hade kvar sin organiska ytbeläggning och en metallbeläggning i det andra försöket. Den huvudsakliga aspekten som undersöktes var kolfibrernas förmåga att klara tillverkningsmiljön. Det förekom inga intakta kolfiber efter processen i försöken med EBM och SLM med den organiska ytbeläggningen. Beträffande SLM-försöket, påträffades även stora håligheter där kolfiber befunnit sig, vilket visade på en bristfällig impregnering av fibrerna innan deras nedbrytning. Fibrerna som var belagda med en metall överlevde framställningsprocessen i en större utsträckning, men impregnationen var fortfarande bristfällig. Metoderna som undersöktes i denna rapport var sålunda inte lämpliga för att tillverka en kolfiberkomposit med stålmatris.

Fiber/matrix interface cracking plays an important role in determining the final failureof unidirectional (UD) composites. When subjected to longitudinally tensile loading,fiber/matrix interface debonds originate from fiber breaks or initial defects propagatealong loading direction. Depending on the quality of fiber/matrix interface, debondscould keep growing longitudinally which leads to the degradation of compositestiffness or kink out of interface and connect with neighboring debonds or fiberbreaks that forms a so called critical fracture plane which leads to the final failure ofUD composite. For UD composite subjected to transversely tensile loading, theinitiation, growth and coalesce of arc-shape fiber/matrix interface debonds result inthe formation of macro-size transverse cracks, the propagation and multiplication ofthese transverse cracks, although would not directly lead to the final failure ofcomposite, could cause significant stiffness degradation of composite structures.In the presence thesis, the growth of a fiber/matrix interface debond of a UDcomposite with hexagonal fiber packing under longitudinal and transverse tensileloading was investigated numerically, with the special focus on the influence ofneighboring fibers. In the current study, energy release rate (ERR) is considered as thedriving force for the debond growth and was calculated based on J Integral andVirtual Crack Closure Technique (VCCT) using finite element software ANSSY.Papers A – C in the present thesis deal with the influence of neighboring fibers on theERR of a debond emanating from a fiber break under longitudinal loading condition.In longitudinal loading case, debond growth is mode II dominated. In paper A, anaxisymmetric model consisting 5 concentric cylinders that represent broken fiber withdebond, surrounding matrix, neighboring fibers, surrounding matrix and effectivecomposite was generated. It’s found that there are two stages of debond growth, thefirst stage is when debond length is short, the ERR decreases with increasing debondlength, and the presence of neighboring fibers significantly increase the ERR ofdebond. For relatively long debond, the debond growth is steady when ERR is almostconstant regardless of debond length. In steady state of debond growth, the presenceof neighboring fibers have little effect on the ERR. In papers B and C, a 3-D modelwas generated with broken fiber and its 6 nearest fibers in a hexagonal packed UDcomposite were modelled explicitly, surrounded by the homogenized composite. Based on the obtained results, it’s shown that ERR is varying along debond front, andhas its maximum at the circumferential location where the distance between two fibercenter is the smallest. This indicates that the debond front is not a circle. For steadystate debond, the presence of neighboring fibers have little effect on averaged ERR(averages of ERR along debond front). For short debond, the presences ofneighboring fibers increases the averaged ERR, and that increase is more significantwhen inter-fiber distance is the smallest. Paper D investigates the growth of afiber/matrix debond along fiber circumference under transverse loading. It’s foundthat debond growth in this case is mixed-mode, and both mode I and mode II ERRcomponents increase with increasing debond angle and then decreases. Debondgrowth is mode I dominated for small debond angle and then switch to mode IIdominated. The presence of neighboring fibers have an enhancement effect on debondgrowth up to certain small debond angle and then changes to a protective effect. InPaper E, the interaction between two arc-size debond under transverse loading isinvestigated. It’s found that when two debonds are close to each other, the interactionbetween two debond becomes much stronger, and that interaction leads to the increaseof ERR of each debond significantly, which facilitates further growth for bothdebond.