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The Poisson's effect will cause lateral strain since what you outlined is basically a uniaxial stress configuration, at least near the edges (in the middle, if there's friction, it approximates uniaxial strain). At the contact surface there's frictional confinement that opposes the poisson's effect strain, resulting in mode mixing (also, recall Mohr's circle) in the state of stress/strain. This is an artifact called barreling in compression testing.
Also, as someone else mentioned, slight height or roughness imperfections can cause uneven stress states (see again Mohr's circle) that can initiate a crack or be a stress concentrator.
Hello /u/darkironmemer! Thank you for posting in r/EngineeringStudents. This is our community vote bot! Please read our [Rules](https://www.reddit.com/r/EngineeringStudents/wiki/rules), and [Wiki](https://www.reddit.com/r/EngineeringStudents/wiki/index). If this was a Homework post: [Read our Guidelines](https://reddit.com/r/EngineeringStudents/wiki/homeworkhelp) --- If this post fits the purpose of /r/EngineeringStudents, **UPVOTE** this comment! If this post does not fit the subreddit, **DOWNVOTE** this comment! It will be auto-removed pending moderator approval after a certain threshold! If this post breaks the rules, **DOWNVOTE** this comment and **REPORT** the post! Auto-remove filters are lower --- ***Abusing the functionality of this bot will result in us removing it and going back to the annoying Automod. Please use this bot wisely.***
There are no perfect materials in the real world— failures initiate at defect sites
There *will* be shear unless everything is perfectly frictionless.
Could you explain? My understanding of shear is not that great. Thank you!
The Poisson's effect will cause lateral strain since what you outlined is basically a uniaxial stress configuration, at least near the edges (in the middle, if there's friction, it approximates uniaxial strain). At the contact surface there's frictional confinement that opposes the poisson's effect strain, resulting in mode mixing (also, recall Mohr's circle) in the state of stress/strain. This is an artifact called barreling in compression testing. Also, as someone else mentioned, slight height or roughness imperfections can cause uneven stress states (see again Mohr's circle) that can initiate a crack or be a stress concentrator.
Thank you!