In this paper, we consider a Borel measurable function on the space of $\scriptstyle m\times n$
matrices $\scriptstyle f: M^{m\times n}\rightarrow \bar{\mathbb{R}}$
taking the value $ \scriptstyle +\infty$
, such that its rank-one-convex envelope $\scriptstyle Rf$
is finite and satisfies for some fixed $\scriptstyle p>1$
: $$\scriptstyle -c_0\leq Rf(F)\leq c(1+\Vert F\Vert^p)\ \hbox{for all}\F\in M^{m\times n},$$
where $\scriptstyle c,c_0>0$
. Let $\scriptstyle\O$
be a given regular bounded open domain of $\scriptstyle \mathbb{R}^n$
. We define on $\scriptstyle W^{1,p}(\O;\mathbb{R}^m)$
the functional $$\scriptstyle I(u)=\int_{\O}f(\nabla u(x))\ dx.$$
Then, under some technical restrictions on $\scriptstyle f$
, we show that the relaxed functional $\scriptstyle\bar I$
for the weak topology of $\scriptstyle W^{1,p}(\O;\mathbb{R}^m)$
has the integral representation: $$\scriptstyle \bar I(u)=\int_{\O}Q[Rf](\nabla u(x))\ dx,$$
where for a given function $\scriptstyle g$
, $\scriptstyle Qg$
denotes its quasiconvex envelope.