Thermal performance of TIMs during compressive and tensile stress states

Author(s):  
Cameron Nelson ◽  
Jesse Galloway ◽  
Christopher Henry ◽  
William Kelley
Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1099
Author(s):  
Qingqing Chen ◽  
Yuhang Zhang ◽  
Tingting Zhao ◽  
Zhiyong Wang ◽  
Zhihua Wang

The mechanical properties and fracture behaviour of concretes under different triaxial stress states were investigated based on a 3D mesoscale model. The quasistatic triaxial loadings, namely, compression–compression–compression (C–C–C), compression–tension–tension (C–T–T) and compression–compression–tension (C–C–T), were simulated using an implicit solver. The mesoscopic modelling with good robustness gave reliable and detailed damage evolution processes under different triaxial stress states. The lateral tensile stress significantly influenced the multiaxial mechanical behaviour of the concretes, accelerating the concrete failure. With low lateral pressures or tensile stress, axial cleavage was the main failure mode of the specimens. Furthermore, the concretes presented shear failures under medium lateral pressures. The concretes experienced a transition from brittle fracture to plastic failure under high lateral pressures. The Ottosen parameters were modified by the gradient descent method and then the failure criterion of the concretes in the principal stress space was given. The failure criterion could describe the strength characteristics of concrete materials well by being fitted with experimental data under different triaxial stress states.


2010 ◽  
Vol 97-101 ◽  
pp. 500-503 ◽  
Author(s):  
Jian Wei Li ◽  
Min Qiang Xu ◽  
Jian Cheng Leng ◽  
Ming Xiu Xu

Magnetic behavior of ferromagnetic materials has been using to detect defects of materials. To evaluate the stress states of the components by the magnetic memory signal, Q235 defect asymmetrical samples were made. The characteristics of magnetic memory of Q235 have been studied in the three different testing environments which are online-loading, online-unloading and offline-unloading under cycle tensile stress. The results show that magnetic memory signals have different characteristics in different testing environment. It is feasible to evaluate preliminarily the stress state by the magnetic memory signals.


2011 ◽  
Vol 52-54 ◽  
pp. 2170-2175
Author(s):  
B. Li ◽  
J. Yu ◽  
Suo Qing Yu ◽  
A.B. Wang ◽  
Y.H. Jiang ◽  
...  

The forging method with horizontal V-shaped anvils (HVA) is effective in the control of inner stress states, metal tissue, etc. FEM numerical simulation is conducted for the HVA forging method, under various processing parameters. The results show that during HVA forging, the transversal and axial stress states in the middle part of forgings are influenced by not only the ratio of the anvil width to billet height (anvil-width ratio )but also the ratio of the blank width to billet height (blank-width ratio) and the reduction ratio, while the end parts are influenced little. Among those processing parameters, the reduction ratio plays an important role. When the reduction ratio is 5% or 10%, it is possible to obtain axial and transversal tensile stress. When the reduction ratio is larger than 15%, it is easy to obtain two-way compressive stress. Therefore, in order to control the two-way tensile stress, big reduction ratio should be adopted. Small blank-width ratios result in the forgings cracks because of transversal tensile stress in common flat-anvil stretching method. On the contrary, even if the blank-width ratio is small, transversal compressive stress can be generated in forgings for the HVA forging method, only if the matching of the anvil-width ratio and the reduction ratio is suitable. The feature of the HVA forging method benefits the preventing forgings from inner cracks. The results provide the theoretical foundation for the application of the HVA forging method.


2010 ◽  
Vol 2010 (DPC) ◽  
pp. 000737-000758 ◽  
Author(s):  
Craig D. Hillman ◽  
Randy Schueller ◽  
Greg Caswell

The effects of low Tg underfill material on the reliability of high-Pb first level interconnects were assessed through elastic-plastic finite element modeling and inspection of failure sites at the first-level interconnect. Temperature-dependent changes in specific underfill parameters (elastic modulus and coefficient of thermal expansion) induced a primary tensile stress within the solder bump. The presence and magnitude of this tensile stress were highly dependent upon the maximum and minimum temperature of exposure. Under certain specific thermal conditions, a form of tensile ratcheting was identified through finite element modeling. The application of tensile stress was found to induce a change in degradation behavior and rates relative to the nominal shear stress state (see Figure). This effectively eliminated distance-to-neutral point as a predictor of first-level interconnects performance and required the development of new models to predict solder bump behavior. A discussion on this transformation in stress states and the potential influence on changes in part qualification procedures are provided.


1988 ◽  
Vol 126 ◽  
Author(s):  
Edward Y. Chang ◽  
Gregory T. Cibuzar ◽  
Thomas K. Yard ◽  
Krishna P. Pande

ABSTRACTThe passivation of GaAs MESFET's with PECVD silicon nitride films of both compressive and tensile stresses is reported. The shift of MESFET parameters due to passivation was found to be dependent upon gate orientation. For example, it is found that the shifts of threshold voltage are of opposite sign for MESFET's oriented along [011] and [011] directions. Our experiments show that nitride of tensile stress is preferable for MESFET's with [011] oriented gates. The shifts in VTH IDSS and GM of the devices before and after nitride passivation are lesd thaw s% if the nitride of appropriate stress states are used for passivation.Breakdown voltage of the MESFET's after nitride deposition was also studied. It is found that the process with higher hydrogen incorporation tends to reduce the surface oxide and increase the breakdown voltage after nitride deposition.


1999 ◽  
Vol 30 (11) ◽  
pp. 2835-2842 ◽  
Author(s):  
D. M. Goto ◽  
D. A. Koss ◽  
V. Jablokov
Keyword(s):  

Sign in / Sign up

Export Citation Format

Share Document