The load carrying capacity of interbre joints are one of the key entities for build-up of strength inpaper materials. In order to gain insight in how to tailor the macroscopic properties of such materialsby chemical and/or mechanical treatments at a microscopic level, direct measurement of individualbre{bre crosses are typically performed. However, the state of loading in the interbre joint, intesting of individual bre{bre crosses, is in general very complex and an increased understandingfor how to evaluate the mechanical properties of interbre joints is desirable. In Paper A, amethod for manufacturing and measuring the strength of isolated interbre joints is presented. Themethod is applied to investigate the strength of bre{bre crosses at two dierent modes of loading.Also, an investigation on the manufacturing conditions is presented. The strength distribution ofindividually prepared bre{bre crosses is characterized and it was found that the median strengthin a peeling type of loading was about 20% compared to samples tested in the conventional shearingtype of loading. In Paper B, a procedure for evaluating interbre joint strength measurementsin terms of resultant forces and moments in the interbre joint region is presented. The methodis applied to investigate the state of loading in bre{bre crosses tested in peeling and shearing,respectively. It is shown that for a typical interbre joint strength test, the load components otherthan shear, cannot in general be neglected and is strongly dependent on the structural geometry ofthe bre{bre crosses. In Paper C, four distinctly dierent load cases; peeling, shearing, tearingand a biaxial type of loading was tested mechanically and evaluated numerically in order to gainmore information on how interbre joints behave in dierent modes of loading. In Paper D, thein uence of a chemical additive on the interbre joint strength is investigated on the microscopic(joint) scale and correlated to the eect previously observed on the macroscopic (sheet) scale. Xraymicrotomography and image analysis was used to understand structural changes in the brousnetwork in terms of the number of interbre joints as well as the average interbre joint contact area.The results showed that the median interbre joint strength increased by 18% upon adsorption, andthat the polyelectrolyte increased the number of contacts between the bres as well as an increasedarea of contact. In Paper E, the damage behaviour of individual interbre joints is analyzed. Froman extensive number of mechanical tests, the typical damage behaviour is identied and a failurecriterion is used to study the in uence of failure properties to give indications on how to tailor thematerial to optimize the joint strength. / En av de viktigaste mekanismerna for den lastbarande formagan hos pappersmaterial ar brottegenskapernahos berfogarna. For att eektivt skraddarsy sadana materials egenskaper genom kemiskoch/eller mekanisk behandling samt for att forsta hur sadana modieringar paverkar egenskapernapa en mikroskopisk niva ar provning av individuella ber-ber-kors en allmant anvand metod. Belastningeni en berfog vid sadan provning ar dock generellt komplicerad och ytterligare kunskapom hur berfogars mekaniska egenskaper skall utvarderas ar onskvard. I Artikel A, presenterasen metod for tillverkning samt mekanisk provning av isolerade ber-kors vid tva olika typer avbelastning. Vidare undersoks hur torktrycket, torkmetoden samt graden av malning inverkar pafogstyrkan. Resultaten visar att brottlasten for en globalt akande belastning var omkring 20 % avbrottlasten for prov utforda med den konventionella skjuvande belastningen samt att styrkan hosindividuellt tillverkade berkors ar fordelade enligt en Weibull fordelning. I Artikel B, presenterasen numerisk metod for utvardering av fogstyrke-matningar med avseende pa kraft- och momentresultanternai gransytan mellan brerna. Metoden anvands for att studera belastningsmoden hosber-kors i tva principiellt olika lastfall. Resultaten visar att for ett typiskt berfogsprov, kan intelastkomponenterna, vid sidan av skjuvning, generellt forsummas da de ar starkt beroende avber-korsets geometri. I Artikel C, jamfors fogstyrkematningar under fyra principiellt olika lastfall; akande, skjuvande, rivande samt biaxiellt. De experimentella last-forskjutningskurvorna, samtde beraknade lastmoderna anvands for att undersoka vilket tillskott pa information de foreslagnalastfallen kan ge i hansyn till fogstyrkan hos massabrer. I Artikel D, undersoks en polymers (somabsorberats pa berytorna) inverkan pa saval berniva som pa natverksniva. Fiberfogstyrkan matsexperimentellt och eekten av den kemiska tillsatsen jamfors pa mikroskopisk niva (ber-kors) medtidigare uppmatt eekt pa makroskopisk niva (ark). Rontgentomogra och bildanalys anvands foratt undersoka de strukturella skillnaderna som uppstar i de brosa natverken vid absorption av enpolyamin och resultaten visar att antalet berfogar per berlangdenhet samt att medelkontaktareanokade. Resultaten visar ocksa att medianen av berfogsstyrkan okade med 18 %. Dessa eekter sammantagetar anledningen till varfor polyaminer, sasom PAH, ar sa eektiva for att oka torrstyrkanhos pappersmaterial. I Artikel E, karakteriseras skadebeteendet hos individuella berfogar franett omfattande antal matningar. Ett brottkriterium infors i den numeriska utvarderingsmetoden foratt studera skadebeteendet. Kanslighetsanalys och inverkan av brottparametrarna studeras ocksafor att ge indikationer pa hur egenskaperna kan skraddarsys for att optimera berfogstyrkan. / <p>QC 20140527</p> / BiMaC Innovation